Learning to Live with Charles Bonnet Syndrome

Learning to Live with Charles Bonnet Syndrome

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“In the evening, I like to watch the news. That’s when my ‘visitors’ most likely appear,” she said with a little laugh, glancing at her daughter. And then back to me: “I know they’re not there, but I find them interesting.”

“Oh, she sees funny things,” said the daughter. “She has Charles Bonnet Syndrome.”

I was in an intake interview with the pair before placing a caregiver in the home of this delightful 95-year-old woman with macular degeneration. We had been talking for about 40 minutes before she mentioned her “visitors.” It was already clear that she was fully oriented, sound-minded, intelligent, witty, and sharp. “When this first started, I thought I had gone crazy, but I know now I haven’t,” she said. “Now I just sit back and watch the show. Having Charles Bonnet Syndrome is like seeing a little movie, though it is quite strange.”

Hallucinations of vividly clear, complex patterns, people, faces, buildings, cartoons, children and animals – often in amazing detail – would be understandably disturbing and frightening. But this woman had learned that this trick of the mind happens to some people who have had vision loss. Hers was the healthiest reaction to Charles Bonnet Syndrome (CBS) I had ever seen.

CBS – named for the Swiss naturalist who first described it in 1760 (Bellows) – is little discussed and not widely known. Because I work with many elderly people, I know it because there is so much macular degeneration among the aged. It is the leading cause of blindness in those over 60 (National Institutes of Health and the National Library of Medicine). It is not thought to be rare, though it is likely vastly underreported: those who experience it are terribly frightened they have become crazy or demented, so they don’t dare mention their visions. (Menon, Rahman, Menon, and Dutton, 2003). However, it may occur in as many as one-third of visually impaired people (Light House International).

Such silence and fear are not entirely unreasonable. CBS can be misdiagnosed and often goes unrecognized by medical professionals (Menon, G., Rahman, I., Menon, S., and Dutton, G., 2003). Families often panic. Patients reporting such symptoms should be checked medically against the possibility of other causes, such as neurological diseases or medication side effects. CBS also can occur where damage or disease affects the area of the visual cortex of the brain. Those who experience it without known visual impairment should be checked for other conditions. (Royal National Institute of Blind People).

15 Tips for Managing Charles Bonnet Syndrome

There is no cure for Charles Bonnet Syndrome, so patients need to learn to live with and manage it — all too often on their own and in silence. Some patients can develop depression or anxiety as a response to CBS. There are, however, a variety of steps that can be taken to support low vision patients at risk for CBS, and to minimize its negative emotional effects:

  1. Every health care practitioner, person with low vision, their family and caregivers should be educated about CBS.
  2. Medical personnel need to learn how to correctly screen for and diagnose CBS (Menon, G., Rahman, I., Menon, S., and Dutton, G., 2003).
  3. An approach to screening that makes it easy for patients to admit their symptoms must be in every physician, nurse and nurse practitioner’s toolkit. (Menon, G., Rahman, I., Menon, S., and Dutton, G., 2003). “You know, many people who have vision loss see things that aren’t there. It’s called Charles Bonnet Syndrome. These are nothing to worry about, but they can be upsetting if you don’t know that. Have you ever experienced anything like this?”
  4. Any depression or anxiety should be treated appropriately with medication, counseling or some other applicable therapy (Light House International; Roberts, 2004).
  5. “Normalizing” the experience is absolutely vital, but without being dismissive of any upset the visions may cause the person. “Yes, lots of people have CBS, and they think they’re going crazy or have dementia, but they’re not… who wouldn’t think at first that they’ve lost their mind?” (Royal National Institute for the Blind)
  6. CBS patients should be encouraged to talk about their visions rather than remain silent about them. (RNIB; Menon, G., Rahman, I., Menon, S., and Dutton, G., 2003)
  7. CBS usually stops within 12 to 18 months. Reminding the patient of this every so often can be helpful. “Oh, did you have one of your Charles Bonnet episodes again? What did you see? I hope it didn’t upset you too much. You know, it should go away in time.”
  8. A good sense of humor can help in adjusting well to CBS (Roberts, 2004). Family and health care professionals can affirm lightheartedly how strange and bizarre the visions can be. Jokes about what is seen can be made, but only if the patient finds them amusing.
  9. Fascination for the images and the wonders of the brain can help reframe CBS from a problem to an “experience.” “Isn’t it amazing how the brain is stimulating itself by making all those amazing images! Did you know you had all of these tucked away in your head? Your brain is just so remarkable!” “Butterflies flying out of your toaster? School buses driving down your hallway? What creativity!”
  10. Refrain from psychoanalyzing the images to look for their deeper meaning – they do not yield productively to psychological interpretation. They are not the product of past trauma or unresolved feelings (Saks in Kiume, 2009).
  11. Remind the experiencer that they have from the start had the wisdom to recognize that these visions are not real, though at first they may have had some doubts. When meeting moments where they may not be certain, examining the clarity and detail is often telling; hallucinations might be sharper than the person’s remaining eyesight allows (RNIB).
  12. Since CBS episodes happen more often during “down time” than when the person is actively engaged in activities or with other people, decreasing their incidence may require finding ways to reduce social isolation, boredom, lack of stimulation, and low activity (Roberts, 2004; Murphy, 2012; Menon, Rahman, Menon, and Dutton, 2003).
  13. Sometimes, eye exercises — such as looking from left to right without moving one’s head for 15 to 30 seconds — can help stop a hallucination.
  14. Increased room lighting can sometimes prevent an episode of CBS visions if they commonly take place in low light (Murphy, 2012; RNIB).
  15. Some report that stress and fatigue can exacerbate CBS. Reducing causes of and increasing coping skills around stress, and getting enough rest can sometimes help (RNIB).

While CBS can be frightening and stressful, there can also be positive outcomes. American author, humorist and cartoonist James Thurber lost vision in one eye as a child due to an accident. He reported many visions of strange things afterwards. It is suspected that he had CBS, and that these hallucinations fueled his amazing imagination. His hilarious stories and cartoons may have been a direct result of Charles Bonnet Syndrome (New World Encyclopedia).


With increasing understanding of the role of the brain and mind in health, and rightly so, here is a TED talk with Oliver Sacks, the great neurologist and writer. In terms of pain we must think about the different dimensions (physical, cognitive, emotional) and how they integrate in the individual according to their blend of genetics, experiences, epigenetics (how these two come together), their beliefs, behaviours and environment. This is very much the way in which Oliver Sacks addresses his patients, as individuals and not as conditions. I learned this very early from reading his work and observing healthcare in practice. It is the only way that is tangible and effective.

Here is the bio: ‘Neurologist and author Oliver Sacks brings our attention to Charles Bonnet syndrome — when visually impaired people experience lucid hallucinations. He describes the experiences of his patients in heartwarming detail and walks us through the biology of this under-reported phenomenon.’

“Scanners Live in Vain”

The Great Pain of Space was discovered by early space explorers going out into deep space, and never returning, having been driven mad and suicidal by the void inflicting agony on the human body, requiring total deprivation:

“. . . and when the first men to go Up and Out went to the Moon, what did they find?”

“Nothing”, responded the silent chorus of lips.

“Therefore they went further, to Mars and to Venus. The ships went out year by year, but they did not come back until the Year One of Space. Then did a ship come back with the First Effect. Scanners, I ask you, what is the First Effect?”

“No one knows. No one knows.”

“No one will ever know. Too many are the variables. By what do we know the First Effect?”

“By the Great Pain of Space”, came the chorus.

“And by what further sign?”

“By the need, oh the need for death.”

Vomact again: “And who stopped the need for death?”

“Henry Haberman conquered the first effect, in the Year 3 of Space.”

“And, Scanners, I ask you, what did he do?”

“He made the habermans.”

“How, O Scanners, are habermans made?”

“They are made with the cuts. The brain is cut from the heart, the lungs. The brain is cut from the ears, the nose. The brain is cut from the mouth, the belly. The brain is cut from desire, and pain. The brain is cut from the world. Save for the eyes. Save for the control of the living flesh…They live in the Great Pain while ordinary men sleep in the cold cold sleep of the transit…They make men live in the place where men need desperately to die.”

…What could any Other know of the Up-and-Out? What Other could look at the biting acid beauty of the stars in open Space? What could they tell of the Great Pain, which started quietly in the marrow, like an ache, and proceeded by the fatigue and nausea of each separate nerve cell, brain cell, touchpoint in the body, until life itself became a terrible aching hunger for silence and for death?

…“Is it true that you have conquered the Great Pain?”

Stone hesitated, seeking words for an answer.

“Quick, can you tell me how you have done it, so that I may believe you?”

“I have loaded ships with life.”


“Life. I don’t know what the Great Pain is, but I did find that in the experiments, when I sent out masses of animals or plants, the life in the center of the mass lived longest. I built ships—small ones, of course—and sent them out with rabbits, with monkeys—”

“Those are Beasts?”

“Yes. With small Beasts. And the Beasts came back unhurt. They came back because the walls of the ships were filled with life. I tried many kinds, and finally found a sort of life which lives in the waters. Oysters. Oysterbeds. The outermost oysters died in the great pain. The inner ones lived. The passengers were unhurt.”

“But they were Beasts?”

“Not only Beasts. Myself.”


“I came through Space alone. Through what you call the Up-and-Out, alone. Awake and sleeping. I am unhurt.”

It is an example of the gothic & surreal fantastical elements with an almost visual intensity that render Smith’s SF unique, and earned descriptions like “sheer originality of concept” for the pain of space and the guild founded to deal with it (and later, speculation that Smith was also “Kirk Allen” & derived story elements from hallucinations of future lives).

The pain of space is generally interpreted as reifying a metaphorical or philosophical reaction to space or Smith’s own life at the time (a theme that would appear in other works as well, see TvTropes’s “Space Madness”), due to the overall theme that the other members of the guild had themselves become insane (in a moral sense) due to having been severed from their senses in a classic ‘mind vs body/ heart’ conflict. The SF Encyclopedia describes the surgery as “with an effect on their behaviour that resembles severe autism”, and D’Ammassa’s Encyclopedia of Science Fiction (pg324) comments “Smith examines a variety of themes in the story: the conflict between duty to a small group as opposed to society at large, the unfortunate consequences of divorcing emotion from reason and compassion from action.” Hellekson (The Science Fiction of Cordwainer Smith⁠, pg87):

The Great Pain of Space and Martel’s personal feelings of panic and despair are more mature expressions of the young Paul Linebarger’s [Cordwainer Smith] terror, when Smith’s self-understanding and maturity allowed him to write of the thing that as an adolescent he simply feared. Most critics have read the Great Pain of Space as a metaphorical working of the author’s psychological despair, though I would also link it to the terror of death that Paul Linebarger expressed sixteen years before he wrote “Scanners”. Perhaps Smith’s fundamental fear of the comprehension of death drove this psychological despair, which was likely exacerbated by his endemic health problems. Elms, in his entry on Cordwainer Smith in James Gunn’s New Encyclopedia of science Fiction (1988), notes that “Scanners” is a “story remarkable for its depiction of the desperate steps necessary to control the psychological pain induced by long-distance space travel” (422), although I would note that in “Scanners”, the pain unprotected spacefarers experience is real and physical this real pain is read as psychological. Gary K. Wolfe, in his analysis of “The Game of Rat and Dragon” 2 ⁠, notes that “the ‘pain-of-space’ itself…and human vulnerability to the dragons are further evidences of man’s physical and psychological vulnerability and alienation in space” (“Mythic Structures”⁠, 148). 3

These seem like reasonable interpretations. After all, everyone is well aware that obviously humans can go to space without problem & spend years in orbit: while there are negative health effects like weakened bones or cardiovascular systems (reduced blood), and occasional acute issues like under high acceleration or motion sickness, or psychological issues related to stress & confinement & lack of nature, and well-understood issues of ordinary radiation from cosmic rays or the sun, there is certainly no “Great Pain of Space”. It is a fantasy element, a romantic SF metaphor intended to be reflective of primitive fears of the unknown & personal isolation. Or is it?

How to Remain Independent Despite Low Vision

This telephone discussion features Orli Weisser-Pike, a doctor of occupational therapy and a certified low vision therapist. She has over eighteen years of clinical experience in a wide variety of settings and has for the past decade specialized in treating people disabled by vision loss.


BrightFocus Foundation
“How To Remain Independent Despite Low Vision”
Transcript of Teleconference
May 28, 2014
1:00 p.m. – 2:00 p.m. EST

GUY EAKIN: Hello, everyone, and welcome to our monthly BrightFocus chat presented by the BrightFocus Foundation. My name is Guy Eakin. I’m a Ph.D. and also the Vice President of Scientific Affairs at the BrightFocus Foundation. Today we are going to talk about living independently with low vision. So, unlike previous calls, no drugs, no needles—what can we do in our daily lives with just a little bit of help and training?

Like last time, if you would like to submit a question at any time during today’s call, please press *3 to submit your question to an operator. And if for some reason you are disconnected from the call, here is the number to call back in. It’s 877–229–8493. You’ll then be asked to punch in an ID code, and that ID code is 112435. So that’s 877–229–8493, ID 112435. All our calls are recorded and we will give you more information on recordings and transcripts later in the call.

Our guest today is Dr. Orli Weisser-Pike, a doctor of occupational therapy and a certified low vision therapist. She has more than 18 years of clinical experience in a wide variety of settings and has specialized in treating people disabled by vision loss. Dr. Weisser-Pike is the 2014 recipient of the Recognition of Achievement Award given by the American Occupational Therapy Association. She is currently Assistant Director of Low Vision Services at the University of Tennessee where she also serves as a professor in the Department of Occupational Therapy.

Dr. Weisser-Pike, thank you for joining us. I’ve had the opportunity to speak with you previously and I have to say, you have a lovely accent. I imagine that our listeners will be trying to pin it down. Am I correct that this is a South African accent? Maybe with a bit of local Tennessee flavor?

ORLI WEISSER-PIKE: You’re right, Guy. Well good day to everyone and thank you for joining us today. Guy you’re correct. I was born in South Africa and I moved to the United States 18 years ago for my first job as an Occupational Therapist, but I promise I will speak slowly and clearly so hopefully people will understand what I’m saying.

GUY EAKIN: That sounds absolutely great. So, without any further ado—You started to tell us a little bit about yourself and a little bit about your practice, but maybe you can expound on that and tell us about the type of patients you see and what you try to achieve with those patients.

ORLI WEISSER-PIKE: I am an occupational therapist and a low vision therapist. My role is to help develop relationships between people with low vision and their doctor. I also try and make sure that patients have the appropriate types of devices that they need, that are prescribed by their eye doctor, and I try and help my patients learn the skills that they need to use their devices. I make recommendations for patients to help them to adjust their environment, modify their environment. Maybe they need to modify their routine. I try to help patients understand the disease that they have and also dispel some common myths about vision and blindness. I also—a thing that is very important for me—is to help caregivers as well, understand vision loss of their loved ones. So the patients that I see in the clinic range in age actually, from children all the way to, I’ve had centenarians in the clinic.

Most of the people that I see have low vision as a result of an age-related eye disease. Some that come to mind would be macular degeneration, glaucoma, diabetic retinopathy, cataracts, and sometimes retinal occlusions—so, little mini strokes in the eye. Some patients have had a stroke and they’ve had vision loss from the stroke.

As I mentioned, I also do see children. Our university has an affiliation with St. Jude Children’s Research Hospital which is headquartered over here in Memphis, Tennessee. It’s a cancer hospital. Our eye doctors provide the eye care for those children and I do get to see children who have vision loss as a result of the cancer, or sometimes a result of the treatment of their cancer. But in the majority of the cases are senior with age-related eye diseases

GUY EAKIN: What unites everything together there is that loss of vision. Certainly you are at the frontline and in this really amazing place to really understand what vision loss is. Because you are helping people work within their daily lives, not just as a drug, but within their daily lives to understand how to cope with this. I guess the first question we have is how does macular degeneration—that’s what the focus is of our foundation—how does macular degeneration first announce itself? And what I mean by that is: What am I apt to be doing when I first realize that I am losing vision? Will I have difficulty reading? Will bathroom tiles move? Will they blur? So, what can you tell us about when you first notice macular degeneration?

ORLI WEISSER-PIKE: So the number-one reason that people go to see their eye doctor is because they have trouble reading. Most often people want a stronger prescription, they want a new pair of glasses. People will notice that words look blurry, or words run together, and sometimes the print might look faded. It becomes especially difficult when there’s not enough light for reading or when the words are printed on a colored background. So, people might notice that their reading has slowed down a great deal and that they have to sound out words or that they have to go back and look at words again and only when they look back, they see what they’ve actually missed. It can be very frustrating.

I’m glad you brought up the examples of the bathroom tiles moving. What you are referring to is a phenomenon called metamorphopsia. Some people describe the window blinds being wavy or lines of print looking wavy rather than straight, and this is an early sign that there are changes in the retina. So metamorphopsia, what I’m busy describing, is most noticeable when a person closes one eye and looks with the other eye only. But, unfortunately, people don’t go around looking at things with one eye at a time we use both of our eyes. Our brain does a very good job covering up metamorphopsia when we use both of our eyes together.

I’d like to take this opportunity and make an important announcement to anyone on the call today who has been given an Amsler Grid by their eye doctor. Now, you may not know what an Amsler Grid is, or you may not know that it’s called an Amsler Grid, but an Amsler Grid is a test of your own vision. It is a grid of approximately 3x3 inches square, usually black lines against a white background, with a dot in the center. The instructions are to look at the centered dot and notice if the lines look wavy, or blurred, or distorted, or if there are any areas that are missing from the grid. Now, I want to remind the listeners that you must do this test with each eye separately while the other eye is closed. This test is a way to tell if you are experiencing metamorphopsia or other changes in your vision. If you notice changes you must let your eye doctor know.

GUY EAKIN: Well, I want to take a moment to say that those Amsler Grids that you mentioned are certainly available through or by giving us a call at 1–800–437–2423. We will send those right out to you. I also want to take a moment to remind you that if you have questions at any point during this conversation just press *3 and you will be taken out of the call, taken to an operator, who will take down your question and then you’ll be returned to the call.

As you begin to describe the early stages of macular degeneration, when should people come see you? Maybe you can give us a real-world example of what’s a point where you can say, “You know, it’s time to come in and see a specialist.”

ORLI WEISSER-PIKE: Okay, well that’s a very good question. Certainly, if you’ve been told by your doctor that your vision cannot be corrected to normal by eye glasses, or medications, or surgery, and if you have an eye disease or a condition that is affecting your vision, or if you have been told that you have low vision, then you are ready to see a low vision therapist or another rehabilitation professional that works with people with vision loss. Even if your eye doctor tells you there is nothing more that he or she can do for you, or if there is no treatment for your vision problem, then you can always seek help from a vision rehabilitation professional.

Also, if you purchased any optical devices like magnifiers and telescopes, you will need to learn how to properly use them for the right job. I often see patients who have magnifiers that end up in a drawer because they were never taught how to use them correctly. This creates a dangerous cycle of despair because patients then believe that nothing is going to help them, which is not true. So no matter how small or how great your vision loss is, I want to let you know that there is hope and there is more that can be done to help you as a person.

A rehabilitation professional, like an occupational therapist or a low vision therapist, will not be able to restore your vision. But, we will be able to help you function using new tools, and new methods, and new resources. The good news is that the field of low vision therapy is expanding. As more knowledge and education is becoming available, especially in occupational therapy, there are more services that are available as well.

GUY EAKIN: You bring up a couple different professions. I think we will have to come back and maybe talk about some of the differences between the different types of therapists one could see. There is a question that comes up time and time again with our audiences and before we move on to the actual question-and-answer period, I have one burning question. You have a difficult job. You have strong and independent patients, who are facing some very difficult questions. One of the ones that comes up all of the time is driving. As a professional, how do you help people think about that question but still do what’s right and protect their independence?

ORLI WEISSER-PIKE: I’m really happy that you brought up this topic of driving. It is very difficult to talk about driving cessation. It is a complicated issue because many of my patients live in suburban and rural areas where there are no alternatives or options for public transportation or even taxi cab services. Regardless of my personal feelings or opinions about it, I am obligated to inform my patients of the law. So, the vision requirements to obtain and renew a driver’s license vary from state to state, but the common factor in all states is a minimum best corrected visual acuity, meaning the minimum sharpness of vision between 20/40 and 20/60 depending on the state.

Now some states also have a visual field requirement, meaning that when looking straight ahead, one sees so much to each side. Some states allow people to use a specialized telescope for driving called a bioptic telescope, but not all states allow this device. For example, the states of Tennessee and Mississippi allow people to use bioptic telescopes for driving but the state of Florida, for example, does not allow these devices. And even with the bioptic telescopes, there are certain requirements that must be met. These again vary from state to state.

Now, I want to emphasize that bioptic telescopes are specialized telescopes that are fitted to the patient by an eye doctor. So they are custom-made for each patient. They are not for everyone or for every eye condition. Please don’t try to drive with a telescope even if it is allowed in your state, unless you have been prescribed, fitted, and trained in the use of a bioptic telescope for driving.

So there are several places where you can find out about the visual requirements of driving. A very good website is, and it has on its website a webpage called State Vision Screening and Standards for License to Drive. That is a comprehensive document that lists state-by-state what the requirements are for driving. The National Highway Transportation and Safety Administration also lists on its website state licensing requirements and reporting laws. In some states physicians are required to report patients who do not meet the legal requirements to drive.

GUY EAKIN: I thank you for that and certainly if anybody who does not routinely go onto the Internet would like to call into the BrightFocus Foundation and have somebody help walk them through some of those resources, then that’s what we are here to do. The number is 1–800–437–2423. We are going to move from that particularly sensitive question onto others that are equally important that are going to be submitted by our callers.

I would like to take this time to remind people that if you want to submit a question, just dial *3 and it will take you to that operator who will take that question down. We will try to answer as many questions as we can that are representative of callers’ interests on the topic. After the chat, you can call that BrightFocus telephone number or visit our website at to see how these questions have been answered, also to get large font transcripts and download recordings of this phone call.

One of the first questions that we have really tails on the fact that you gave a really nice description of what signals might prompt us to say come see a low vision specialist. We have questions from listeners. Maurice from Connecticut was one of the ones asking, that asked about that term low vision itself. She asked “how low is low vision.” What is a good definition for low vision? Should we get confused when we hear terms like legal blindness or that dreaded word blindness used interchangeably with low vision?

ORLI WEISSER-PIKE: Yeah, sometimes those definitions are confusing. So the basic definition of low vision is vision that is not correctable by surgery, medication, or glasses—meaning not correctable to normal. When we talk about low vision we really rely on two visual functions and that is the sharpness of vision, otherwise known as visual acuity, and the visual field, which is how much you see all around you while you are looking straight ahead. So, sometimes people will call that peripheral vision. The start of low vision is when somebody’s sharpness of vision is 20/60, or worse, and if somebody has visual field defects in both eyes. That kind of gives you an understanding of where low vision starts. We have normal vision, which is 20/20 vision, near-normal, which is 20/30 to 20/40, and low vision starts at the point where functionally people can’t read newsprint. The size of newsprint, more or less, is at the level of 20/50 visual acuity. Again, as I mentioned with visual field defects if somebody has areas of missing vision, islands of missing vision, or complete areas of side vision that are missing, or tunnel vision, these defects in both eyes, that again meets the definition of low vision.

Now, legal blindness is a legal definition and it’s a severe level of low vision which starts at 2200 or worse and also if somebody has a visual field that is smaller or narrower than 20 degrees, they are also considered to be legally blind. The definition of blindness—blindness is less well defined, but blindness does not mean a complete absence of light. In fact, when we talk about blindness, it includes people with low vision as well.

People that are completely without sight represent a very small percentage of the population of people who have vision loss. So, the word blindness can be confusing and it is even more confusing because a lot of very helpful organizations have the word blind in them: For example, the American Foundation for the Blind, an organization that provides tremendous resources to the public. It is for people with low vision, legal blindness, and total vision loss. It can be confusing, Guy.

GUY EAKIN: Thank you. So with that landscape established with some of the terminology let’s move quickly onto some of the other questions. We have Tom from Rhode Island asking about telescopic glasses. I think very importantly, he is asking what are they but also, how long would it take to be able to use them? How would you address Tom if we were in your clinic?

ORLI WEISSER-PIKE: So I would tell Tom that a telescope is an optical device which is commonly used to magnify things that are far away. Most people might be familiar with binoculars for bird watching, or opera glasses for watching a play. A hunting rifle might have a scope that helps a person aim on the target. These are all examples of telescopes. Some telescopes are designed for use with two eyes, like binoculars, and some telescopes are designed to be used with one eye only, and these are called monoculars—monocular telescopes. Some are designed to be worn, like glasses, some are handheld, and some telescopes are designed to be embedded into a pair of glasses like bioptic telescopes for driving that I mentioned earlier.

There are many skills that need to be learned in order to use a telescope effectively and these all depend on the design of the telescope. For example, if a person uses a monocular telescope for reading signage in a grocery store, he or she will first need to learn how to line-up the telescope with his or her better eye, aim it at the target—or aim it at the sign—and focus the telescope while staying steady.

Now if a person uses a pair of head-worn telescopes, those would be telescopes that fit over your ears like a pair of glass—and people use those to watch television—he or she would need to learn how to focus the glasses as well. Learning to use bioptic telescopes for driving is essential if you are going to use those and get behind the wheel. In any event, if you are using telescopes please, please, never walk while looking through a telescope. You might hurt yourself.

GUY EAKIN: Let me ask a question. We are talking about these low vision specialists and you certainly have a wealth of tools. You have telescopes, you have other devices—but how do I find you in my community? Where would I go to find out where a low vision specialist might be situated?

ORLI WEISSER-PIKE: Oh gosh. So, I would start by asking your eye doctor. In 2007, the American Academy of Ophthalmology developed an initiative called the Smart Science Initiative and it encourages all Ophthalmologists, at the very least, to offer patients with low vision information about local resources. So if you see an optometrist as well, ask him or her about low vision specialists in your area.

You can also contact the Academy for Certification of Vision Rehabilitation and Education Professionals. If you are going online, they are at Now this organization certifies three professions. They certify low vision therapists, orientation and mobility specialists, and vision rehabilitation specialists. There are about 300 certified Low Vision Therapists in the United States.

You can also contact the American Occupational Therapy Association. There are currently about 40, four-zero, occupational therapists with specialty certifications in low vision.

GUY EAKIN: We also offer through our website a low vision support group fact sheet. We would certainly be happy to help you with that. We are starting to hear a lot of terms. I can only imagine that we have people with one hand on the telephone and one hand on pen and paper. So, let us do the pen-and-paper part. Just call in, give us a couple of weeks, and we will have a transcript available for you. I’m going to ask a question that has a lot of alphabet soup associated with it. Is there a particular degree for all of these professions that you mention, is there a particular sequence of letters that we should see after someone’s name that would let us know we are in the right office?

ORLI WEISSER-PIKE: Oh my! That really is an alphabet soup, Guy! So please bear with me. There are four acronyms that indicate that a person has specialized knowledge and skills in low vision. A CLVT is a Certified Low Vision Therapist. A CVRT is a Certified Vision Rehabilitation Therapist. A COMS is a Certified Orientation and Mobility Specialist. And the last one is a SCLV. Now, that is Specialty Certification in Low Vision. This last one, the SCLV, is only given to an occupational therapist, but an occupational therapist may also have any of the certifications mentioned previously.

GUY EAKIN: I’m going to change courses a little bit. We have had a number of questions that are asking, outside of those devices, what are the things that people can adapt their homes to do, to improve safety, and make some of those tasks in the home easier to perform?

ORLI WEISSER-PIKE: Okay, that is a great question about how you can adapt your home. The first thing you can do really easily is to improve the lighting in your home. Did you know, Guy, that light bulbs lose their brightness over time? Light bulbs lose their brightness, and dirty light covers also take away some of the brightness of the bulbs. Cleaning the fixtures and replacing old bulbs with newer energy-efficient bulbs can make a big difference. Of course, lighting is personal and it is subjective, and what works for one person may not work for another person.

In my practice, a common type of light bulb that many of my patients like—especially in overhead ceiling fans and in places like cupboards, pantries and the laundry room—is a compact florescent bulb that is equivalent to 100 watts and is the daylight color temperature, not soft white or bright white. I would not recommend traditional incandescent bulbs or halogen bulbs because they produce a lot of heat and they are unsafe.

Never, ever place a bulb that has a higher wattage than the fixture it is rated for. This is extremely dangerous and can cause your house to burn down. In fact, I have treated a patient who not only lost his house, but lost family members, as a result of a house fire where there were bulbs that were placed in fixtures that weren’t rated for their wattage. It is a terrible thing to do. Another thing you can do to make your home safer is to remove any loose rugs or secure them to the floor. Clutter, in general, can make it very difficult to find what you need, but even more so when a person has low vision. Try to organize items and keep similar items grouped together. For example, place your cleaning materials in a caddy or a bucket. Keep things in the same place, and certainly do not be afraid to get rid of things that you are not using. So try and clean up some of the clutter.

Another recommendation is to make sure that kitchen cabinets are always kept closed. One sure way to injure yourself is by leaving a kitchen cabinet open and then bumping into it with your forehead. I’ve seen those kinds of accidents and they’re not very pretty. You can also store things according to how frequently you use them. Put plates and cups in cabinets that are easy to reach. Put items that you rarely use, for example a punch bowl, in cabinets that are lower or higher.

One last recommendation: I always recommend keeping a tray on the counter. You could pour your coffee or orange juice, or any other beverage in a cup that is placed on the tray, and that way, if you have an accidental spill it will be contained in the tray and hopefully won’t mess up the kitchen floor.

GUY EAKIN: Those are wonderful. I think some of those are ones that we haven’t really heard about before. For anyone who goes onto the internet and looks for these, my experience is you see a lot of the same sorts of tips. One of the things that I think the low vision specialist profession is offering is that relationship. These are people who have sort of seen and heard it all in terms of techniques for around the home. I really encourage people to take advantage of these low vision specialists.

One of the things that I personally hadn’t heard before—I had a friend tell me the other day—and Kathy, if you are on the line I am talking about you—she said she puts a sticker on her sliding glass door and that’s because she can’t tell the difference between a clean door and an open door. It’s one of those things that make sense, but it really just takes talking to someone who has been down that road to know that that’s one that is worth doing. Those are unexpected things for dealing with low vision, but you probably have some experience with symptoms that might be unexpected or aspects of low vision, in general, that people didn’t realize they would have to accommodate. Could you tell people what types of experiences they might be surprised to find themselves confronted with?

ORLI WEISSER-PIKE: Ah, I think Guy that you might be asking me about Charles Bonnet Syndrome (CBS) is that right?

GUY EAKIN: Well, that would be one of them sure.

ORLI WEISSER-PIKE: I’m really glad you asked me to talk about this Charles Bonnet Syndrome. Some people may have never heard of it, but it happens to many people with vision loss. Some studies estimate that between one-and-two thirds of people with low vision have it. Charles Bonnet Syndrome is characterized by visual hallucinations, which are also called phantom visions. People with Charles Bonnet Syndrome see things that are not there. These visual hallucinations can take many forms, like patterns, people, animals, bird, buildings, comic book and fantasy characters, and anything else imaginable.

Charles Bonnet was a Swiss naturalist and philosopher who lived in the 1700s. He was the first person to describe the syndrome, after his father, who had cataracts, told his son about the visions that he was having. Charles Bonnet Syndrome can be very frightening or worrisome for someone with vision loss, especially if he or she has not been informed of the possibility of experiencing visual hallucinations. Many patients tell me that they feel very relieved to learn about Charles Bonnet Syndrome because often they think they are losing their minds to Alzheimer’s disease and are afraid to tell anyone about it. The visual hallucinations in Charles Bonnet Syndrome have very specific characteristics. Usually the person becomes aware that the hallucinations are not real, even though they may be very vivid and clear. In fact, sometimes the hallucinations are sharper, more colorful, and clearer than the person’s typical vision with low vision.

Another distinguishing feature of Charles Bonnet Syndrome is the hallucinations are only visual and they do not interact with you, meaning that you do not hear them, you don’t smell or feel things that aren’t there. The hallucinations can appear at any time of day. Sometimes, they fit with the background of what you are seeing, which gives them an understandable feeling of being real. Sometimes, they may interfere with what you are trying to see and they can last for a short period of time, like a few minutes, or they may last longer.

There is no medical cure for Charles Bonnet Syndrome. Some people find a way of getting rid of the hallucinations by changing what they are doing. Some people find that if they move their eyes from side-to-side, the hallucinations will dissipate. Some people find that brighter light lessens hallucinations. There is no single technique or cure for getting rid of these hallucinations. The good news is they do tend to lessen overtime and people do adjust to having them.

There are some great resources for learning more about Charles Bonnet Syndrome and, again, I am going to recommend some websites. One is and both have great Web pages about Charles Bonnet Syndrome. Also, the British website, that’s the Royal National Institute of Blind People in England, also has very good information about Charles Bonnet Syndrome.

GUY EAKIN: We don’t have terribly much time but I do want to try to hit one more question. We had a question show up that was kind of interesting. I’ve been trying to take a lot of questions and summarize them, but this one was a little bit unique. This was a man named Russ from Illinois, I think, and he asked “If someone has poor vision in only one eye, how can visual confusion be minimized?” How do you keep the good eye and the bad eye from tricking each other? Is that something that a low vision specialist can help with?

ORLI WEISSER-PIKE: That is a very good question and something that usually happens when people are used to sighting with one eye. So, there is something called eye dominance. Just like we have a hand that we use to write with, which is our dominant hand, we also have an eye that we typically use to sight with. When somebody loses vision out of that eye that can make it difficult to adapt to that. It is usually easier if the difference between the two eyes is very great. If the difference is small then it might be even more so.

One thing that I would recommend, for example if there is difficulty reading, I would take a piece of clear tape and just put it over the lens of the glasses of the side of the dominant eye—the eye with poorer vision—just as a temporary occlusion, something to obscure the vision out of that eye so the person is only looking with the better-seeing eye for the task that they are trying to do—for example, reading. That is usually a task that people have difficulty with.

When it comes to using optical devices, again, it would be most beneficial if you see a therapist and learn to line the devices up with the better eye. Sometimes people want to still use the dominant eye, even though it is the poorer-seeing eye and they don’t get good, reliable, visual information through that eye. So again, working with a low vision therapist can really help to minimize the visual confusion.

GUY EAKIN: Thank you so much, and we’re coming to the end of the period we have set aside for our call. I really want to take a moment to thank you so much and express appreciation to Dr. Weisser-Pike for taking the time to speak with us today and certainly thank everyone who joined the call and submitted a question. As I mentioned earlier, we will be posting a recording and a large font transcript of the call on our website. You can also get to that by just calling us at 1–800–437–2423

You can also listen to and download past chats on Apple iTunes and SoundCloud. Best of all, this is all free of charge. You can get to those prior calls. Give us a week or two, and we will get this one up there as well.

Our next chat will be next month and it will be on Detecting the Early Signs of Macular Degeneration. It will be Wednesday, June 25th, at 1 p.m. EST, 10 a.m. PST. We certainly encourage you to register and submit questions in advance, and we will be sending you a reminder email if you have already registered on this call. In fact, you can register for the June chat right now, and you can also request free low vision materials like our safety brochure, Safety and the Low Vision Driver or the Amsler Grid that I mentioned earlier in the call. Again you can do that by calling 1–800–437–2423 or by visiting our website at Again, that’s 1–800–437–2423 or

We’d love to get your feedback on these chats and we would like to do that by asking you one short question, and the best part is you can use your keypad on your telephone to answer the question. Here’s the question: Overall, how would you rate this telephone chat? If you would take the time to press 1 for “very helpful” 2 for “somewhat helpful” and press 3 for “not helpful at all,” then we would find that really helpful to ourselves for bettering this program in the future. So again that’s: 1 for “very helpful,” 2 for “somewhat helpful,” and 3 for “you need to do a little bit more work.”

While you’re doing that, we will remind you that the BrightFocus Chats are held on a monthly basis and to find out about upcoming chats just give us a call or check our website for updates. You can also find out about us by liking us on Facebook, if that is something you use. We are also out there on Twitter, Pinterest, and all of those other social media platforms.

Thank you, everyone, for your feedback. If you’d like to leave us a comment after the call just stay on the line. Thanks, and from all of us at the BrightFocus Foundation: Have a great day.

Amsler Grid – A grid of horizontal and vertical lines used to monitor a person's central visual field

Charles Bonnet Syndrome – The experience of complex visual hallucinations in a person with partial or severe blindness

COMS – Certified Orientation and Mobility Specialist

CVRT – Certified Vision Rehabilitation Therapist

Metamorphopsia – A defect of vision in which objects appear to be distorted usually due to a defect in the retina

SCLV – Specialty Certification in Low Vision

The information provided here is a public service of BrightFocus Foundation and is not intended to constitute medical advice. Please consult your physician for personalized medical, dietary, and/or exercise advice. Any medications or supplements should only be taken under medical supervision. BrightFocus Foundation does not endorse any medical products or therapies.

What is Retinitis Pigmentosa?

Retinitis pigmentosa (RP) is a genetic eye disease that causes the light-detecting cells in the retina (light-sensitive lining at the back of the eye) to break down. The symptoms of RP include reduced peripheral vision and night-blindness and sometimes a loss of central vision. In its later stages, people with RP find it difficult to read, drive and engage in many other activities.

An estimated 1 in 4,000 individuals are affected by this sight-threatening condition, and about half of the people who have RP have a family member with RP as well.

Though there is currently no cure for RP, a low vision optometrist can provide low vision aids and devices to help patients with RP continue to function at the highest level possible. If you or a loved one has been diagnosed with RP, contact , for a low vision consultation.

Singing to the Plants

In December 1913, psychiatrist Carl Jung first experienced what he was later to call active imagination. However, he did not talk about these experiences until twelve years later, when, in May and June 1925, he spoke for the first time of his inner development at two sessions of a series of weekly seminars he was giving in Zurich. The contents of these lectures were not published until 1989 but a partial account of these experiences was given in 1962 by Aniela Jaffé in Memories, Dreams, Reflections, a purported autobiography of Jung which she largely wrote. This account is the foundation myth, the charter, for active imagination.

In 1913, according to this account, Jung, profoundly distressed at his break with Freud, began to experiment with different ways to enter into his own imaginings. As James Hillman describes it, “When there was nothing else to hold to, Jung turned to the personified images of interior vision. He entered into an interior drama, took himself into an imaginative fiction and then, perhaps, began his healing — even if it has been called his breakdown.”

In this imaginal world, Jung began to confront and question the figures who appeared to him and, to Jung’s surprise, those imaginal persons spoke back. “Near the steep slope of a rock,” Jung says, “I caught sight of two figures, an old man with a white beard and a beautiful young girl. I summoned up my courage and approached them as though they were real people, and listened attentively to what they told me.” Again: “I held conversations with him, and he said things which I had not consciously thought. For I observed clearly that it was he who spoke, not I.”

One of these imaginal people, a wise pagan whom Jung named Philemon, “seemed to me quite real, as if he were a living personality.” Philemon spoke to Jung as follows: “He said I treated thoughts as if I generated them myself, but in his view thoughts were like animals in the forest, or people in a room, or birds in the air.” It was this imaginal Philemon who taught Jung the reality of the psyche — “that there is something in me which can say things that I do not know and do not intend.”

There is good reason to believe that active imagination in fact falls in the class of what have been called metachoric experiences — hallucinations, lucid dreams, out-of-body experiences, and — despite Jung’s own dislike for “voluntary imagination,” which he considered to be superficial and trivial — the sort of eidetic visualization that lies at the heart of Tibetan Buddhist ritual meditation. What these experiences have in common is that they

  • occur with the force of a present perception of external reality
  • have what appear to be the same quantity and quality of sensory detail as ordinary experiences
  • are experienced as external to the experiencer and
  • occur in what seems to the experiencer to be an extended and three-dimensional perceptual space — the sort of space which one can explore.

A patient with Charles Bonnet syndrome who sees a convingingly real three-dimensional monkey sitting on his neurologist's lap is having a metachoric experience. So is a lucid dreamer who decides to float down a staircase, or someone who hovers looking down at his own body during a surgery. For example, this is an episode of active imagination that seems clearly to be metachoric:

These metachoric experiences can be characterized along two dimensions — first, according to the degree to which the experience is entered into intentionally and, second, by the amount of control the experiencer exercises over the content of the experience. Active imagination, for example, would be high in intentionality and low on control eidetic visualization would be high on both and a Charles Bonnet hallucination would typically be low on both.

The same type of experience may occur in different places along these dimensions on different occasions. For example, hallucinations of the deceased are a commonly documented part of the grief reaction. Such experiences are typically low on intention, but may vary on control, to the extent that the bereaved attempts, for example, to engage the deceased in conversation, or perhaps even attempts to call the deceased for purposes of communication. A lucid dreamer may — or may not — be able to control the actions of dream objects and persons, or be able to do so to varying degrees.

Several things follow from this discussion. First, it seems that ayahuasca experiences specifically, and shamanic experiences generally, pretty much fall within the class of metachoric experiences. Shamanism seems, for example, to rank high on intentionality and relatively low on control, like active imagination. While the shaman can control his or her own actions while interacting with the spirits, the shaman has no direct control over the actions of the spirits the shaman can ask a question, ask for help, even demand compliance, but most commonly cannot compel a particular response.

Tying shamanism to such experiences as lucid dreaming, active imagination, and eidetic visualization raises a number of interesting questions. Apart from their phenomenology, what do they have in common? A naïve ontology might postulate that the mechanism must be neuropsychological. I am not so sure that is true. I am not sure it is even looking in the right place.

Predictive Processing and Trauma

Not only does the PPF have the means to explain the effects of traumatic experience on the nervous system more generally, it also has the structural resources to explain the differing effects of different kinds of trauma. The differences we present (which we do not take to be exhaustive by any means) are, first, between Type 1 and Type 2 trauma, and, second, between PTSD and trauma-based psychosis. But first, we show how it can help to account for a phenomenon that is central to trauma, namely, dissociation.


It is widely accepted that trauma can lead to dissociation [see, e.g., van der Kolk and Fisler (1995), Putnam et al. (1996), and many more], and that dissociation is in turn associated with a number of mental disorders, including psychosis, PTSD, depersonalization disorder (DPD) (see, e.g., Moscowitz et al., 2008). The concept of dissociation is intended to capture a certain detachment or disconnection that someone might feel toward their current perceptions and emotions, or toward their experiences of the world around them more generally (Lynn and Rhue, 1994). In relation to trauma, dissociation comes in two very different varieties: peritraumatic and post-traumatic (Ursano et al., 1999). Peritraumatic dissociation consists in a detachment from what is happening during a traumatic event [it can also lead to amnesia with regards to that event (e.g., Freyd, 1994)]. Post-traumatic dissociation consists in a general and more long-lasting sense of detachment from the world in the aftermath of a traumatic event. In extreme cases, this leads to a diagnosis of DPD.

Dissociation in general, and these types of dissociation in particular, can be nicely accommodated within the PPF. The crucial notion within the PPF for this purpose is the notion of hierarchy. To state the account plainly, and subsequently flesh it out: dissociation involves a disconnection of the lower levels of the hierarchy from the higher levels.

Recall that the lower levels of the hierarchy deal with more sensory and concrete happenings in the world, and operate at faster timescales. Thus, at these lower levels your nervous system selects hypotheses about what is happening in terms of shapes, colors, sounds, and at mid-levels, in terms of objects and events. However, an extremely important feature of the overall multi-level hypothesis that constitutes a normal experience is not just that this is all happening, but it is happening to you. Thus, built into the overall hypothesis is a self-model. How this self-model is constructed and fits into your nervous system’s dynamic hypothesis construction is currently being explored [see Letheby and Gerrans (2017) and Millière (2017) who both examine ego dissolution from within the PPF]. Whatever the finer details, it would certainly be very high up in the hierarchy: a-modal, highly abstract, temporally extended over long timescales, etc. If the prediction-error (bottom-up signaling) from the low-level and mid-level hypotheses is blocked or down-modulated, the resulting experience will be one where something is happening (colors and sounds at the lower levels, objects and events at higher levels, etc.), but it is not experienced as happening to me. If this is short-lived and occurs only during a traumatic event, then what we are talking about is peritraumatic dissociation. If this is a general state of affairs that is brought to bear on the experience of the world generally, then we are talking about post-traumatic dissociation, and potentially a dissociative disorder (or even depersonalization).

This is what dissociation looks like within the PPF, but why would it occur? Most models of peritraumatic dissociation build on the classic work of Janet (1904) who claimed that dissociation was a protective mechanism, allowing traumatic experiences and memories to be compartmentalized and thereby minimize distress (see, e.g., van der Hart et al., 2010). We think that this is undoubtedly along the right lines. Within the PPF, distress, namely, the subjective experience of strong negative affect, is to be understood as the generation of a hypothesis about what is happening to oneself that is mainly designed to minimize prediction error from interoceptive sources (namely, bodily change) (see Seth, 2013). One way to minimize distress would be to hypothesize that the events are not happening to oneself. Then, in line with this, the relevant bodily changes are also not hypothesized to be taking place, and, as a result, the negative affect is then heavily, or perhaps even entirely, mitigated.

So far this is in keeping with the vast majority of accounts of why dissociation takes place (see Dell and O’Neil, 2009). But such accounts view the natural drive toward minimizing negative affect as so self-evident (indeed, even trivial) that this amounts to an explanatory bedrock. Within the PPF we can take things one step further by reflecting on the biological nature and purpose of negative affect. It is to motivate the organism to get rid of it, to make it act so as to improve its current situation (Van de Cruys, 2017). Thus, the PPF’s re-framing of the dissociative mechanism is not just about the negativity of the event, but also about one’s helplessness in the face of the event in question [see Peters et al. (2017) for an account of stress within the PPF along these lines]. The negative affect is quarantined (and ultimately reduced/eliminated) through dissociation when it is clear that it can no longer be of help to you: it cannot motivate you to get out of the current situation because it is clear that you can’t get out of it 5 .

One outstanding question is: What makes dissociation persist in cases of post-traumatic dissociation? The more obvious answer is to say that we are talking about a similar state to the state of peritraumatic dissociation, but where the drive toward distress-minimization (self-protection) is extended through time. Everything the dissociated subject experiences (and not just the traumatic event) is happening but is not happening to them. A less obvious answer would be to say that post-traumatic dissociation is, in spite of superficial similarities, different in its underlying nature from peritraumatic dissociation. Perhaps, for example, the self-model is not disconnected from lower levels of the hierarchy, but has somehow been broken or disintegrated. The possibility of this happening, and how it might happen, is at this stage highly speculative, but this is an interesting area for future research and theorizing [the work of Letheby and Gerrans (2017) and Millière (2017) on ego dissolution in the context of psychedelic drug-taking might offer some clues here].

Type 1 vs. Type 2 Trauma

In Type 1 trauma, a single traumatic event of cataclysmic and usually life-threatening significance leaves its mark of person’s nervous system. The symptoms of Type 1 trauma tend to be distress in the presence, and avoidance, of cues that are a reminiscent of the event. Sometimes these environmental or even self-produced cues (e.g., patterns of thinking/imagery) yield vivid flashbacks (Brewin et al., 2012).

Here is how the PPF makes sense of Type 1 trauma. What happens, when the traumatic event is experienced, is that a multi-level hypothesis is selected which corresponds to the conscious experience of the traumatic event. Part of that hypothesis, that conscious experience, is its life-threatening significance. As a result, selecting that hypothesis is something that your nervous system just cannot miss in the future 6 . What this amounts to in Bayesian terms is a hypothesis that, due to its importance for survival, is given an unusually high prior probability. That biases the selection of that hypothesis such that it will be selected even when the fit with the input is relatively poor. And, as we saw, hypothesis selection determines the conscious experience at that time. That is why something merely reminiscent, even only vaguely so, can act as a trigger, and lead to a vivid reliving of the event. Thanks to the hierarchy, this needn’t be experienced as an actual reliving of the event. The higher-level hypothesis concerning where and when the subject is remains intact (and hence accurate) and therefore there is often an awareness that, although intensely unpleasant, and potentially highly disruptive, this is “just a flashback” (Brewin, 2015).

Matters are further aggravated since the perceived fit of the hypothesis is made stronger by interoceptive feedback loops. What we mean is that, not only is the hypothesis of supreme significance, it is also heavily affectively charged. Thus, it needn’t be that something reminiscent of the traumatic event be directly mistaken by your nervous system for the traumatic event itself. Rather, what will often happen is that the trigger will give rise to an interoceptive affective state that will itself need explaining along with the sensory evidence (Pezzulo, 2013). To take an example, if you return to Figure 1, suppose you have just seen a horror movie and are in a generalized state of fear. The “wind” hypothesis may have a higher prior probability, but the burglar hypothesis would now have a better fit, since it would not only explain the squeaking window, but also the fear that you feel. Similarly with trauma, the traumatic hypothesis has better fit since it not only explains (albeit poorly) the sensory evidence it does a pretty good job of explaining your affective state too. This is a �k loop” because the trigger need only initially result in a relatively mild emotional state, which then promotes something closer to the trauma hypothesis, which in turn will lead to a stronger emotional state, which in turn will lead to a more determinate and negative hypothesis, etc. In short, there is a vicious cycle leading to progressively more powerful affective states, and progressively more negative hypotheses that are drafted in to explain them away (this can also be put in terms of 𠇌ircular inference,” see Jardri and Deneve, 2013).

In Type 2 trauma, what we have is a more general type of learning, over an extended period of time. The result of this is an impression, built up from statistical regularities in past experience, that the world is not generally a kind or safe place. What this does is lead to more general biasing toward threatening hypotheses, rather than the reliving of a very specific, rich, and multi-level hypothesis (as is the case with Type 1 trauma).

This means that events are given more negative and threatening interpretations than they warrant, which in turn leads to high levels of negative affect, of anxiety and hypervigilance. This in turn would lead to a vicious cycle since the propensity toward negative affect would bias perceptual inference in favor of negative hypotheses in the same way as the feedback loop mentioned above. A positive or neutral hypothesis explains only exteroceptive signals, but is actually at odds with interoceptive signals (with negative hedonic valence), namely, your negative emotional state. Your nervous system effectively “reasons”: “Why would I be afraid if this situation was innocuous?” A negative hypothesis on the other hand explains both exteroceptive and interoceptive signals. You instead get: “I’m afraid, therefore there must be something to be afraid of.” This goes some way toward explaining the hypervigilance and startle response that we see in individuals who have undergone Type 2 trauma.

Of course, the distinction between Type 1 and Type 2 trauma won’t always be clear-cut, and many people will present with symptoms of both. All that you would need for this symptomatic presentation is for a single event of cataclysmic significance to make one multi-level hypothesis have aberrantly high prior probability (Type 1 flashbacks) and for either that same event, or (more likely) an extended period of threat in addition to that one event, to lead to a general skewing of priors toward negative hypotheses, namely, to the learnt view that the world is not a safe place.

PTSD vs. Trauma-Based Psychosis

It is well established that there is a strong statistical relationship between trauma and psychosis (see Morrison et al., 2003). How does psychosis differ from PTSD, and where do we draw the line between the two? The line may not be clear-cut in terms of the extent to which some cases of PTSD have elements of psychosis, but the concepts “PTSD” and “psychosis” are very different. Psychosis, in its purest sense, means a disconnection from reality. To the extent that one can be more or less disconnected from reality, psychosis comes in degrees people can be more or less psychotic (in other words, psychosis can vary from mild to severe). On the other hand, someone can experience PTSD flashbacks, but recognize them as such, dismiss them as not telling them anything about the world (and rather as revealing something about their own mind, rather than the world) and hence will not be disconnected from reality. They will not, as a result, take themselves to inhabit a world that is different from the actual world. We take it that many cases of PTSD are non-psychotic in this sense. In psychosis, however, the person takes herself to be living in a world that is different from the actual world: she has an inaccurate world-view, is disconnected from reality. Now, of course, someone could, due to their past (i.e., involving trauma) and symptomatic presentation, have a diagnosis of PTSD, but also present with psychosis, namely, with some degree of disconnection from reality. There are two questions to address here.

(i) What does this amount to in predictive processing terms? And how does the difference between non-psychotic PTSD and post-traumatic psychosis play out?

(ii) What does the PPF tell us about how these two different cognitive states might arise?

The key to answering (i) lies in the hierarchical arrangement of hypotheses. “Lower” in the hierarchy, the hypotheses correspond to percepts. Thus, an inaccurate hypothesis at this level corresponds to hallucination or illusion. At higher “levels” what we are talking about are beliefs, more abstract reflections of the subject’s world-view. Hypotheses at the lower level don’t need to entail that hypotheses higher up fall into place: they can be, and often are, compartmentalized. The clearest example of this is in cases of optical illusions. You can measure the lines in the Muller-Lyer illusion to prove to yourself that they are the same length, but your visual system will still �lieve” that they are different lengths. Here your high-level hypothesis (i.e., your belief) is that the lines are the same length, even though your visual experience, determined by a lower-level hypothesis, is telling you the contrary. To take an equivalent but more ecologically valid example, somebody can hear a voice, but dismiss that as merely the product of their nervous system (Nayani and David, 1996). Alternatively, they could update their world-view, and take there, for example, to be an autonomous agent who is communicating with them. The former case is not (contrary to what some diagnostic manuals might tell you) psychotic, whereas the latter is. Aberrant sensory experiences need not lead to full-blown psychosis. Furthermore, the intensity of the aberrant experiences needn’t correlate with the extent to which the experiences are taken seriously. This can be clearly seen in Charles Bonnet syndrome, where subjects have intense visual hallucinations, which they always recognize as “just in the head” and not real (Berrios and Brook, 1982).

Another factor is to do with the content of the hypotheses selected, which constitute these experiences, and the extent to which they can be connected to the past by the person having the experience. In Type 1 trauma the hypothesis (and hence the experience) is of a specific event from the subject’s past, and so there is less temptation to think that the flashback is part of the current world. In Type 2 trauma, the hypotheses that correspond to the symptomatic experiences are less specific and hence less obviously associated with the past, although the person may still be aware of the association, and hence also able to reject them as something that’s not happening in the here-and-now. In psychosis, the hypotheses tend not to be highly specific, tend not to be connectable to a distinct past event, and they tend to be about current experience. This capacity to appreciate whether the experience is about the past or the present, and how the specificity of the hypotheses in question is a factor in this, may go some way toward explaining why some people experience psychosis after trauma (Brewin, 2015). It also helps to explain why the line between PTSD and psychosis is blurred (Powers et al., 2016), and more likely to be blurred specifically between Type 2 rather than Type 1 trauma and psychosis.

In answer to (ii), we need to give an account of what is likely to lead to aberrant hypotheses higher up the hierarchy, rather than the sort of compartmentalized hypotheses we see in, for example, non-psychotic PTSD. This requires us to reflect on the kinds of trauma and, in particular, the way in which trauma will have different impacts at different stages of the life-course. More pervasive aberrations are more likely to be caused at times when basic priors are being laid down, namely, early in life when general and fundamental learning takes place. These basic priors may not determine specific factual beliefs, but rather styles of thinking general statistical appreciation of what is a plausible inference to make. Trauma early in life, and especially at the hands of a primary care-giver, is likely to yield a basic lack of trust in the world (Herman, 1997). This should not be thought of as the acquisition of a belief about the world. Rather it should be seen as a background condition for the way in which beliefs will be formed 7 . To put it in the terminology of the PPF, it is about priors rather than specific hypotheses. Thus, aberrant sensations are more likely, due to this skewing of priors, to lead to aberrant beliefs: the low-level hypotheses, more likely to yield aberrant hypotheses at higher levels in the hierarchy.

For Better Vision, Living in the Dark

Amy and Carl (both pseudonyms) had never met before they decided to move in together earlier this year. Amy was a twenty-four-year-old Upper East Sider with a live-in boyfriend, and Carl was a fiftysomething security guard with two kids. What brought them together was the fact that they have lazy eyes—Amy’s left, Carl’s right.

A neuroscientist, Elizabeth Quinlan, of the University of Maryland, had found a way to treat lazy eyes in rodents by exposing them to an extended period of darkness, after which their brains readjusted to the light, like infants learning to see for the first time. A team led by Quinlan and Ben Backus, of the SUNY College of Optometry, had secured National Institutes of Health funding for a human trial, but, after a search lasting months, Amy and Carl were the only qualified volunteers, aside from a third subject who dropped out after thinking twice about the treatment: living with total strangers, in complete darkness, for ten days.

“I’m worried about waking up and feeling like I’m buried alive,” Amy said, as she and Carl settled into their new home, a small apartment in Crown Heights. The research team had unscrewed all the light bulbs, disconnected the gas stove, and blacked out the windows. (The police were notified that there was nothing nefarious afoot.) The faintest hint of light could invalidate the results, so Amy stepped outside to smoke one last cigarette as Backus explained that his team had installed a series of three doors leading into the apartment, so that meals could be delivered without admitting light. There was no scientific precedent for leaving people together in the dark for so long, so Backus had conducted a dry run in the master bedroom of his house, in New Rochelle. “We’re not letting them drink any alcohol,” he said. “I downed a glass of wine and ended up in the closet.” He had been trying to find the bathroom.

Amy and Carl initially faced the same issues as any new roommates—Amy liked the apartment hot Carl liked it cold—plus those that come with not being able to see. During one dinner, Amy, who is a pescatarian, accidentally forked a piece of chicken off Carl’s plate. The apartment had an exercise bike, and games for learning Braille, but Amy, whose boyfriend wasn’t thrilled that she was living in the dark with another man, worried about growing restless. “I need something to do besides getting dressed in the morning,” she said. There was a guitar in the apartment, and she planned to learn how to play. Carl had a bottle of NyQuil.

The hallucinations began on Day Two. Amy saw a blue triangle above her bed. Carl saw two cubes rotating in space. “They’re starting to fall into classic Charles Bonnet syndrome,” Backus said, citing a condition in which people who’ve gone blind think they can see things that aren’t there. Their other senses seemed to improve—fruit was sweeter, whispers audible—and sounds, like a creaky door, triggered more hallucinations. When the subway rumbled down Eastern Parkway, Amy saw black and gray circles spinning, like wheels. “The coolest one happened last night,” she said, on Day Five, noting a hallucination in which she felt as if she were underground, looking up through a sewer grate, as cars passed in front of a street lamp. The subjects hallucinated most often when they were alone.

The darkness could be overwhelming—an optometrist who visited had to quickly leave—but Amy and Carl adjusted to it, and to each other. They went to bed early and woke up late, feeling less buried alive than back in the womb. Amy didn’t do much guitar-playing, but they sang karaoke using wireless headphones. (On Day Seven, Amy chose a Barenaked Ladies song: “It’s been one week since you looked at me.”) After a few days, they could high-five each other. They reported feeling less self-conscious. “I’m sticking my tongue out right now,” Amy said. “You stay human even though it’s dark,” Carl said.

By Day Ten, however, they were ready to leave. The apartment smelled of mildew. Amy needed a cigarette. Darkness filled their dreams: Carl had had one in which thick black oil flooded his home, while Amy dreamed that, when the lights came on, her lazy eye was cured but she was now cross-eyed. As Backus and Quinlan prepared to turn on the lights, the subjects were warned not to expect immediate improvement. (The results remain inconclusive, with another study in the works.) But when the researchers switched on a one-watt bulb, to help them adjust, and Amy and Carl found themselves able to see for the first time in ten days, both of them reported that, at least for the moment, the world looked sharper than ever. ♦

Clinical presentations

Clinical presentations in adults

Bumping into things: the Pulfrich phenomenon

Delayed retinal processing or delayed conduction from one eye with respect to the other leads to a temporal mismatch of the incoming visual information, which leads to inaccuracy of perception of the position of moving targets in three-dimensional space. 23 This results in an inappropriate compensatory movement of the limbs or body (Figure 2). While this can be considered a peripheral disorder, it is the central interpretation of where things are in visual space that is disturbed and causes problems.

Diagram illustrating the way in which the Pulfrich phenomenon causes an object approaching an eye with delayed conduction to appear to vear towards the affected side. The left eye (blue) ‘sees’ the approaching target ahead of the affected left eye (red). The pathway perceived by the mind is shown in green.

There are a number of presenting complaints that we have found to be common to the diagnosis of the Pulfrich phenomenon. These include:

Swerving inappropriately to avoid oncoming traffic (when the right eye is affected) or parked traffic (when the left eye is affected).

A tendency to knock off wing mirrors of parked cars (left eye affected).

Being unable to replace the tape in a tape recorder whilst driving, because the car is then driven in the wrong direction.

Feeling a need to duck and swerve when going through doorways.

In crowds, swerving to avoid people on the affected side and bumping into people on the other side.

Difficulty with fine tasks such as tapestry.

Difficulty in accurately reaching for door handles.

A sensation that lamp-posts are coming to hit one when sitting upstairs on a double decker bus!

Causes of the Pulfrich phenomenon include dilatation of one pupil (a driving hazard?), demyelinating, traumatic and ischaemic optic neuropathy.

A number of years ago we reported the successful management of a patient with the Pulfrich phenomenon using a pair of glasses with one tinted lens calibrated to prolong the retinal processing time to match the delay on the other side. She still wears these glasses all the time, and we have since managed many similar patients in the same way. Another such patient was in a road traffic accident but was frightened to drive again and had even received psychiatric help. The prescription of spectacles with an appropriately tinted lens in front of the unaffected eye solved her problem instantly! 24,25

Hemianopia and hemianopic blindsight

Brain injuries sustained by soldiers during the First World War led skilled observers such as Gordon Holmes 26,27 and George Riddoch 28 to relate the sites of brain damage to the pattern of visual field loss, which is the basis of our current knowledge of the retinotopic map in the visual cortex.

Riddoch also found that some soldiers with hemianopia due to brain injury were aware, at an ostensibly subconscious level, of intact movement perception in the ‘blind’ hemifield, a phenomenon known as statokinetic dissociation or the Riddoch phenomenon. He also showed that recovery of perception of movement is a good prognostic sign for further recovery. The term blindsight was first coined by Weiskrantz 29 who carried out detailed studies of the persistent visual function in the hemianopic field of a patient who had undergone surgical removal of the right striate cortex.

A practical way of detecting intact perception of movement in a ‘blind’ hemifield is to carry out Goldmann perimetry. The patient is instructed to look at the peripheral target as soon as it is first seen (rather than to press the buzzer) and the eye is viewed by the observer. Isopters, which join the points at which saccades are generated, can then be plotted. Patients who are able to do this can be trained to improve the reproducibility and accuracy of their saccades on the perimeter. 30 Patients who are aware of their hemianopia can also be trained to use large fast eye movements into the blind hemifield, which results in long-term improvements in visual searching and scanning, with associated subjective improvements in visual function in day-to-day life. Patients with stroke receive physiotherapy and speech therapy but such ‘visuotherapy’ has yet to be developed significantly outside the context of research.

Cerebral blindness and blindsight

The following case history gives an insight into the features of persistent, to a large extent subconscious vision, which can be present in those who have lost vision due to bilateral occipital damage.

MC was a skilled personal secretary in her thirties. As a sequel to severe respiratory infection and hypotension she developed bilateral occipital lobe infarctions. We first saw her 1 year later. She was escorted into the clinic by her husband and told us that she had no vision. Indeed she had no vision for anything that was not moving, but both she and her husband were astonished when she accurately named the colours of large moving objects, and when she was able to accurately mirror hand movements being made in front of her with movements of her own hands. However, she was even more surprised that she was able to walk accurately around a number of obstacles placed in her path, when she was encouraged to do so and told that she could. Since then she has learned to move her head from side to side to be able to visualise things in front of her, and she has successfully followed up our suggestion of using a rocking chair to enhance her perceptual abilities. Her descriptions of her vision are fascinating. She can see rainwater running down a window but cannot see through it. When her daughter is walking away from her she can see the pony tail moving from side to side but cannot see her daughter. She can see the movement of the water going down the plug hole but she cannot see her child in the bath. These phenomena were apparent to her before she came to see us, but because she had been told she was blind, she did not have the confidence to believe her own observations. The act of informing her that her experiences were fully in accordance with the concept of intact function in the areas of the visual brain responsible for seeing motion and the dorsal stream pathways responsible for ostensibly subconscious visually guided movement, gave her an understanding of the world as she sees it and now, 2 years later, she is able to navigate within her home independently. It seems that the act of drawing her awareness to her own subconscious vision has been the catalyst to the initiation of her (albeit incomplete) functional rehabilitation.

Impaired simultaneous perception, loss of attention and inaccurate visually guided movement

Rather than discuss contemporary work, 1,2,3,31 for this section I thought I would return to the work of Gordon Holmes 27 published in the British Journal of Ophthalmology in 1918. In an extraordinarily detailed paper he gives the clinical descriptions of six soldiers in whom shrapnel or bullets passed through both posterior parietal lobes. In all six patients, bilateral lesions involved the angular and supramarginal gyri and the splenium internally. Lower visual field loss was seen in four patients due to injury of the superior optic radiations. The cognitive visual problems were very similar in all the cases and closely resembled those described by Balint a few years earlier in a patient with bilateral ischaemic damage to the parietal lobes. 32

An inability to make accurate visually guided movement of any part of the body. This Holmes described as a disturbance of visual orientation and Balint referred to it as optic ataxia (for movement of the upper limbs).

An inability to see more than one or two elements of the overall visual scene—a manifestation described by Balint as simultanagnosia.

An inability to explore a scene with the eyes and to shift gaze from one location to another (apraxia of gaze).

These features, which may be associated with lower visual field loss (due to the superior optic radiations also being affected), are consistent with profound injury to what is now known as the dorsal stream.

In our clinics, however, patients are more likely to present with more subtle deficits of simultaneous perception as their sole problem. The clue to the diagnosis is the patient who says she is unable to read, but who has a good binocular visual acuity for single letters. Two L-shaped occluders can be used to reveal only one or two words at a time. If this allows the text to be read and the meaning is understood, but revealing more words causes confusion, the diagnosis of bilateral parietal dysfunction should be suspected. In our experience this condition is not uncommon but may go unrecognised. Multifocal ischaemic pathology is the most common cause. Some success has been claimed for intensive rehabilitation. 33

Children with impaired vision due to periventricular leukomalacia commonly show a very similar pattern of visual dysfunction 34 and this is discussed later.

Lack of attention and driving

Profound impairments in simultaneous perception and attention due to parietal lobe pathology are rare, but more minor disorders of these functions are relatively common. This has been highlighted by recent work investigating attention in the context of driving. The investigation called the ‘Useful Field of View’ assesses ability to give attention to a brief event in the eccentric visual field while also giving attention to a central event. It investigates visual processing speed and visual attention. Those with low scores are at significantly greater risk of being involved in road traffic accidents. 35

Not recognising people and getting lost

The temporal lobes contain the visual memory banks and allow us to recognise what we are looking at. The process of recognition is served on both sides, but there is a degree of lateralisation of function, with the fusiform gyrus of the right temporal lobe 36,37 primarily serving the function of recognition of people's faces 9,10,11,12,13,38 (except perhaps in left-handed people). 39 Damage to this area 40,41 or the adjacent white matter 42 leads to problems with face recognition or prosopagnosia. There is a range of different patterns. 38 The disorder can be complete or incomplete, or there can be inability to identify faces of new people encountered after the time of the brain damage, indicating an inability to form a memory store of new faces. 43 False recognition of unfamiliar faces is a problem for some people with prosopagnosia. 44 The act of not recognising someone is a complex task. Each person one passes on the street is compared with the memory bank of stored faces, if there is not a match, that person is not recognised. An incorrect match leads to false recognition. There may also be difficulties with object recognition. 45 Recognition of the language significance of facial expression can be preserved 10 or impaired 46 both in adult acquired cases and as a result of brain damage during infancy. 47

Prosopagnosia can also occur developmentally 48,49 in association with normal imaging 50 or with a smaller than normal right temporal lobe 51 and can be a fundamental problem for children and adults alike. (A number of people with developmental prosopagnosia have introduced themselves to this author. They describe the profound problems of not being able to recognise their own children and spouses, and the lengths they have gone to disguise their disability. Other family members have been described as having the same problem and/or profound problems finding their way around.)

An inability or disability in finding one's way around (topographic agnosia) due to right temporal lobe dysfunction, 12 in our experience, is characterised by problems when out and about, difficulties finding the way around in buildings, and problems knowing where things are in drawers and cupboards. The orientational problems are not just visual. There can also be a loss of knowledge about well-known buildings and landmarks when tested from their spoken name.

Prosopagnosia and topographic agnosia commonly occur together 12 and the combination has been reported as a manifestation of migraine. 52

Impaired reading ability

An acquired impairment in reading ability can be caused by a wide range of disorders. 2 When an adult patient says that he has developed difficulty reading in the context of good visual acuity, possible factors to consider are:

Hemianopia. The hemianopia moves as the eyes move. Right hemianopia means that the next word may not be seen. Left hemianopia means that the start of the next line cannot be seen. Vertical reading can help some people considerably, both for hemianopia and for hemianopic neglect due to contalateral parietal pathology.

Alexia. Left occipital infarction extending into the splenium also disconnects the right occipital lobe from the language processing centres on the left side of the brain. This results in inability to read despite the ability to write being maintained.

Impaired simultaneous perception due to parietal pathology means that only a few words can be read at once.

Acquired dyslexia can take many forms and can result from temporal lobe damage resulting in impaired word recognition (particularly with pathology on the left side 14,15 ) and from frontal damage, which can impair language interpretation and visual working memory. 19

Table 1 shows a practical approach one can use in the clinic to determine the cause of acquired reading difficulty.

Persisting vision

If a patient continues to see the details of a visual scene even after looking away from it, this is known as visual perseveration or palinopsia. This condition can occur as a sequel to anterior visual pathway disturbance 53 or as a variant of the Charles Bonnet syndrome 54 but it can also occur as a result of focal occipital or occipito-parietal pathology (more commonly on the right). 55,56,57,58,59,60 Patients can also complain of persistence of their visual imagery as a sequel to a range of psychotherapeutic drugs 61,62,63 or following the use of LSD or ecstasy. 64,65 It is important to be able to make a correct diagnosis because patients with palinopsia have been misdiagnosed as being psychotic. 66 For some patients the condition can be disabling and anticonvulsant treatment, for example with carbamazepine, warrants consideration. 67

Diffuse brain disorders

Progressive acquired dorsal and ventral stream dysfunction Patients with progressive damage to the posterior cortex may develop damage to the dorsal stream system or to the ventral stream system, or both. 68

Progressive dementia (for example, caused by Altzheimer's disease and posterior cortical atrophy) can affect any aspect of visual function. Loss of visual acuity and contrast sensitivity are increasingly being recognised. 69,70 Visual field loss in Altzheimer's disease tends to affect the lower visual fields in an arcuate manner 71 and impaired motion perception has been demonstrated. 72 Degenerative foci in the occipito-parietal area affecting dorsal stream structures can cause great difficulty with visually guided movement 73,74,75 associated with impaired simultaneous perception, which is gradually progressive 76,77 and can be the first sign of dementia. 76 When the occipito-temporal areas (the ventral stream) are affected, alexia, impaired object and face recognition, 78,79,80,81,82,83,84,85,86,87,88 and problems finding the way around 89,90 can be extremely problematic.

Multiple sclerosis can cause difficulties with recognition and identification of objects. The problems include impaired recognition of shape, together with difficulties with identification and naming 91 and can result from occipito-temporal demyelination. 92 Visuospatial problems are also common. 93 Busy supermarkets can be visually overwhelming and patients may not understand why they have to rest after going out shopping while a walk in the park is not so tiring. The focal nature of the pathology means that the problems differ from individual to individual and can affect both those who are cognitively impaired and those who have few other neurological problems.

Visual hallucinations associated with poor vision: the Charles Bonnet syndrome

Lack of visual input can result in the mind creating its own imagery. Prolonged patching of the eyes can lead to both unformed and formed (or complex) visual hallucinations that abate when the patches are removed. Similarly, visually impaired patients may experience complex visual hallucinations. This condition is known as the Charles Bonnet syndrome (named after the author who first described the condition in his grandfather). 94

The hallucinations comprise clear organised images, which appear real in three-dimensional space, over which the subject has little control. They are thought to represent release phenomena due to loss of input from the central visual fields to the visual association areas of the cerebral cortex. Reduced cognitive function accompanying old age, social isolation, and sensory deprivation may be contributory factors.

The most common hallucination is of a person. Disembodied distorted faces, small costumed figures and branching structures, realistic images of animals and figures, subtle geometric forms, well-defined complex figures, faces which can be Lilliputian (miniaturised), normal sized or ‘larger than life’ in black and white, or more commonly, in colour, of varying degrees of complexity have also been described. 54 Functional MRI carried out during hallucinations has shown activity in the ventral occipital lobe tissue with type of hallucination correlating with the known functional anatomy of the occipital lobe. 95

Charles Bonnet syndrome is most common in those with age-related macular degeneration. It frequently goes unrecognised in clinical practice because of both a lack of awareness among doctors and patients' reluctance to admit to hallucinations in case they are thought to be mentally unstable. Patients usually possess insight into the unreality of their visual experiences, which can be pleasant but can cause distress.

Sensitive and sympathetic history taking is required to make the diagnosis. We are finding that as many as 60% of patients with age-related macular degeneration with a visual acuity of 6/36 or worse, if carefully questioned, will describe hallucinations. Reassurance and explanation that the visions are benign and do not signify mental illness have an important therapeutic effect. Improving visual function and addressing social isolation may terminate hallucinatory activity. There is no universally effective drug treatment but anticonvulsants may play a limited role in aborting the hallucinations.

Case report of a patient with a parieto-occipital intra-cerebral haemorrhage

In 1999 a 66-year-old lady sustained an intracerebral haemorrhage (Figure 3). Since then she had had profoundly disturbed vision, which had not been explained to her. When seen recently she described difficulty recognising people's faces and problems of falsely recognising people she does not know. These symptoms are worst when she is under stress. Intermittently she sees people as having the heads of dogs, which are entirely realistic, or people may, on occasion, appear to have no arms. She may see formed visual hallucinations of people standing in front of her. She has great problems finding her way around, both when out and about and in people's homes. She also tends to lose things around the home. The visual acuities are 6/9 unaided in each eye and she has a complete left homonymous hemianopia. This patient has a combination of prosopagnosia, topographic agnosia, Charles Bonnet syndrome and left hemianopia occurring as a sequel to her intracerebral haemorrhage. Explanation of her symptoms combined with suggested strategies for handling her problems have considerably improved her quality of her life.

Axial MRI scan showing an intracerebral haemorrhage, which was found on the other images to extend through the right occipital lobes into the right parietal and temporal lobes.

Clinical presentations in children

Clumsiness in children with squint

The parietal visual function of mapping three-dimensional visual space so that we can move through it gradually develops as we get older. Young children commonly bump into things and it is difficult to know whether a history of bumping into things as a young child is normal or whether the incoordination is visual in origin.

Parents of children who have a squint commonly say that their children have better hand–eye coordination when their eyes are aligned. For this reason we set out to investigate whether accommodative esotropia leads to inaccuracies of movement of the upper limbs. 96 We set up a touch screen and asked children with either right or left fully accommodative esotropia to point at targets on the screen without being able to see their hands. They were tested when their eyes were aligned (while wearing spectacles) and when they were squinting (while not wearing spectacles). Hypermetropic children without squint made up the control group and they too were tested with and without spectacles. The result was that the children with accommodative esotropia pointed inaccurately to the side of the central target erring to the side of the straight eye (when not wearing glasses) but they were more accurate and not different from the controls when the squint was corrected by wearing glasses, thus validating the parents' observations. We suggest that the oculomotor imbalance disturbs the position of the efference copy map, perhaps by disturbing the normal proprioceptive input from the extraocular muscles, which may contribute to co-aligning the picture of the world as we see it, with the real world outside our bodies. (Adults with acquired squint commonly complain of mislocalisation of objects in visual space, presumably for similar reasons.)

Not seeing things that are obvious

Books for young children do not contain a lot of information on each page and the print is large. Magic for young children is easy to perform because they do not notice change in the same way as adults. A young child on a bike shouts ‘get out of the way’ when there is plenty of room. These observations reflect the nature of the developing parietal lobe functions of simultaneous perception, attention and planning movement through three-dimensional space, with the capacity to handle complex visual data progressively increasing with age. 97 But what happens when there is pathology in this area of the brain? Children with dorsal stream dysfunction (which in our experience is most commonly due to periventricular leukomalacia 34 ) can show many features related to dysfunction in this area, which causes difficulty in handling complex visual scenes (Table 2). Finding a toy from amongst other toys or on a patterned carpet or bedspread can be very difficult or impossible. Difficulty in seeing things that are pointed out in the distance is typical. (The further away things are, the more information there is in the visual scene to sort out.) This becomes evident at the zoo when the affected child can only see the animals that are nearby. Busy environments like supermarkets, shopping centres or swimming pools can be difficult to handle. Children can react to these environments in different ways. They can become frightened or they can become disruptive. In contrast, when such children are out on an open playing field, they become content and behaviour can improve significantly. The older child can have problems reading. Print size diminishes with each school year. This leads to progressive crowding of text, which in turn can lead to problems with reading because the text becomes too crowded.

The aim of management is to decrease the amount of incoming visual information at any one time. Providing toys in small numbers on a plain play mat helps the child to focus on one thing at a time. A plain bed cover makes it much easier to find clothes on the bed than a patterned one. Going shopping when it is quiet is much easier. At school, recognition of how much the child is able to handle at any one time facilitates the development and delivery of the curriculum. Enlargement of the text to reduce crowding can help significantly. Correction of small degrees of hypermetropia can provide slight enlargement and thereby decrease crowding. For more severe problems, text can either be masked off so that only a small amount at a time is shown or it can be shown sequentially on a computer screen.

Difficulties with visually guided movement of the limbs

Moving accurately through three-dimensional space requires intact dorsal stream function. Children with periventricular white matter damage or posterior parietal damage due to other causes can manifest profound difficulties in moving through three-dimensional visual space. 98 Inability to differentiate a floor boundary (for example, between carpet and linoleum) means that any such boundary that has not been seen before has to be investigated to determine whether there is a step present or not. Black and white tiled floors can be frightening. When approaching a kerb, the foot may be lifted to the wrong height, too early or too late. Going down stairs is particularly difficult because of the difficulty in judging depth. A banister helps considerably by providing tactile and proprioceptive depth information. Inaccuracy of reach and grasp, while less common, can also be seen. In a recent review of our patients we have identified 40 children with this problem (commonly associated with impaired simultaneous perception) including eight with intact stereopsis, which suggests that the dorsal stream visual pathways serving motion through three-dimensional space may be distinct from the pathways serving stereoscopic vision.

Problems pursuing the target

A common association with impaired simultaneous perception and impaired visually guided movement is inaccurate supranuclear control of gaze. 34 There may be inaccurate saccades and problems with pursuit in such children with brain damage. 99 To what extent this impairs perception of moving targets remains to be elucidated.

Not recognising people and objects

Ventral stream dysfunction associated with difficulty recognising faces is a common feature of damage in the temporal lobe territory. 98 The problem may manifest in different ways, ranging from inability to recognise close family members, to consistent problems of not recognising people when they are seen out of context. Incorrect identification of strangers as being known is typical. Children can become adept at recognising people by voice recognition and other cues. It is only when the other cues are not available, such as a mother standing in a group waiting for her child at a nursery, that the problem becomes apparent when the child runs to the wrong parent. These children are commonly unable to understand the language conveyed by facial expression and may be incorrectly diagnosed as being autistic. A simple test of asking the child to tell you whether you are happy, cross or sad as you adopt the appropriate expressions is very informative. Use of obvious and subtle expressions helps to detect less obvious difficulties. (It is also really worthwhile doing this test for all visually impaired children to determine the facial expression recognition distance. Children who cannot see well often look impassive and may be thought to be poorly responsive, but they can only emulate and respond to what they see.) Difficulties recognising shape and form have also been described. 98,100 Such children can have problems with geometry but cope well with other aspects of maths. They may also have reading difficulties related to letter and word recognition. 101

Difficulty reading

The cognitive processes that are required for reading are complex, but in the context of the child who has neurological pathology here are a few practical points that may prove helpful:

Text needs to be at the size that can be read at maximum speed when the child is tired. (Not at the level of the visual acuity, which is a measure of the smallest text that can be seen.) One must not forget that print size diminishes as each year at school passes.

Check accommodation by dynamic retinoscopy in children with cerebral palsy. 102 We have found that it can be absent in children with dyskinetic cerebral palsy 103 or reduced in other forms of cerebral palsy and a near reading correction can improve reading vision tremendously.

Rarely impaired supranuclear control of gaze can preclude the small eye movements needed for letter by letter reading. Both enlargement of the text and learning to read by the look and say method can prove helpful.

Ventral stream pathology can lead to great problems recognising letters and words, and it is important that children with such pathology are enabled to access information by other methods than reading.

Dorsal stream pathology causing impaired simultaneous perception leads to an extreme form of crowding. The acuity may be normal for single letters but it is profoundly reduced for crowded letters. The teachers often discover that such children can read single words when other text is masked off and sequential presentation of text on a computer screen or by using two black L-shaped occluders can be very effective.

Rarely pathology of the left occipital lobe and the splenium of the corpus callosum means that the word seen by the right occipital lobe cannot be passed to the language brain on the left side and this leads to alexia. Braille has even been advocated in such cases.

Getting lost

Problems with route finding, which can vary in severity, commonly accompany impaired face recognition both in children and in adults (and may be associated with a left homonymous hemianopia). 98 There may be difficulties when out and about, problems finding the way within buildings, for example at school and difficulties remembering where things are kept.

When out and about important routes can be committed to memory by using verbal cues and it can be helpful to talk about landmarks on a regular basis. In the home, colour coding or labelling of doors and drawers can help considerably.

Problems with visual memory

Visual memory is used for copying, drawing, remembering where things are and a host of other tasks. Educational strategies are required, which take these problems into account in children with visual memory difficulties.

Examples of cerebral visual impairment in children

TN is 5 years old. He and his twin brother were born at 24 weeks gestation. He frequently falls and trips over things. (Suggestive of lower visual field impairment.) He commonly walks straight into door frames or even lamp-posts (which is suggestive of optic ataxia). He cannot find a toy in a pile of toys. He cannot see something pointed out in the distance and he runs around in an uncontrolled manner in supermarkets. (These features suggest impaired simultaneous perception.) The visual acuities are 6/12 right and 6/60 left due to left myopia and anisometropic amblyopia.

The visual history and premature twin birth are typical of periventricular leukomalacia affecting the occipital white matter. This was confirmed by MRI scan (Figure 4) which shows a subtle white matter signal in both parieto-occipital ventricular areas and mild dilatation of the right lateral ventricle trigone. There is less white matter in the occipital than in the frontal regions.

Axial MRI scan showing mild dilatation of the right lateral ventricle associated with an abnormal white matter signal in the parieto-occipital areas, and less white matter in the occipital than in the frontal areas.

KS is eight years old. She first presented with a divergent squint at the age of 20 months, but the clue to her higher visual dysfunction came with the history that as a toddler she consistently tripped over obstacles, including her baby sister. She has visual acuities of 6/12 and bilateral peripheral lower visual field restriction. Even when she is looking down, she is sometimes inaccurate in moving her feet over an irregular surface. She can have difficulty with floor boundaries between linoleum and carpet and tests the boundary with her feet to make sure that there is not a step. She manages well with steps and stairs but she has to hold on to the banister. Occasionally, she mis-reaches for objects with either hand. She may either reach too near or too far. She has problems handling complex visual scenes. She has difficulty seeing things which are pointed out to her in the distance (the further things are away, the more detail there is to see). She has had difficulty finding a toy in a toy box (but this is improving) and may easily lose an object on a patterned carpet. When playing a board game, she can ‘lose’ her own counter and has to have her attention drawn to it. She has difficulty in visiting shops and supermarkets because she finds them too crowded and she prefers to avoid them. Educational material has to be simplified because when it is complicated, she can miss out a lot of information. She can easily lose her way. This applies particularly when she is out and about and she has to be given help and directions on a regular basis. Her MRI scan (Figure 5) shows that she has sustained damage to the superior occipital lobes extending into the posterior parietal territory, the origin of which is unknown.

Coronal MRI scan of the posterior parietal area showing bilateral superior periventricular scarring and expansion of the lateral ventricles.

The recognition that KS has these problems has meant that people working with her understand the nature of her problems and are sympathetic to her needs. Educational information is enlarged in order to reduce crowding and is presented sequentially. Her bedroom is decorated in a plain fashion and there is not a lot of clutter. She is also receiving training in how to find her way around.

AC was first seen by us at the age of 6 years. She had been born at term with a normal birth weight. She developed apnoeic seizures 24 h after birth. CT of the brain the following month showed areas of low attenuation in the frontal and parietal areas. As she grew up it became apparent that she was not seeing normally and MRI at the age of 5 years (Figure 6) showed loss of occipital cortex and white matter associated with enlargement of the trigone regions of the lateral ventricles. White matter damage was also seen in the parietal and frontal regions. These were thought to be consistent with hypoglycaemic or possibly hypoxic ischaemic encephalopathy. The visual acuities are 6/18 in each eye. Visual field examination reveals both lower visual field loss and left-sided extinction. She finds slopes and stairs frightening and she moves her feet inaccurately over steps and kerbs. She also reaches for things inaccurately. Complex visual scenes are a problem and she too cannot cope in crowded environments, cannot see things which are pointed out in the distance and cannot find an item on a patterned background. She does not appear to see things which move quickly.

Axial MRI scan showing loss of white matter in the occipital cortex associated with enlargement of the trigone regions of the lateral ventricles. There is also frontal and parietal white matter damage.

She does not recognise her mother or other family members and has difficulty recognising shapes, for example she has difficulty differentiating a slipper from a banana, and she has problems getting lost in new environments. Intermittently she performs like a sighted child when she is in a clear high contrast uncluttered well-known visual environment, and at other times she acts as profoundly visually impaired when in a complex visual scene which she has not previously experienced. After 5–10 min she tires very easily and shows strong avoidance behaviour. She can therefore only tolerate short bursts of working on visual tasks. Three years later she has learned to read using the look and say method. She chooses to read with a little window in a white mask which she moves across the text. This compensates for her impaired simultaneous perception. She uses her memory for hairstyles to compensate for her inability to recognise faces, and all her friends know to introduce themselves. Her ability to see things pointed out from the car has improved considerably.

The most common missed diagnosis

In our experience, the most common diagnosis of visual impairment in children to be missed is periventricular leukomalacia. The lack of periventricular white matter can cause cerebral palsy (particularly spastic diplegia), but it can cause visual problems in isolation. A combination of lower visual field impairment, impaired visually guided movement (particularly of the lower limbs), difficulty extracting visual information from a complex background (in various combinations and in varying degree) which may or may not be associated with motor problems, is common but the diagnosis is easily missed. Additional problems with impaired recognition and a tendency to easily get lost are often associated features.

Cognitive visual problems in children with cerebral palsy

In children with cerebral palsy who can communicate and function socially, the above problems can be apparent in any combination and can be identified. In more profoundly affected children, however, it is very likely that they have cognitive visual problems in equal measure, but they cannot be identified because they are masked by communication and motor problems. However, it is a logical principle, in the context of the education of such children, to simplify the visual world by having limited visual information in the foreground and a plain background, recognising that simultaneous perception is likely to be limited.

Cortical blindness and ‘travel vision’

A reflex visual pathway connects the retina to the the superior colliculi and the pulvinar. This subsystem serves the ability to perceive and react to moving targets at a subconscious level. Some children who have profound loss of vision due to occipital pathology and who have cerebral blindness are nevertheless able to react to moving targets. For example a moving spoon brought in from the side (where reflex visual perception is arguably more effective), may result in the mouth opening. Such children who are mobile may be able to navigate successfully. This form of vision has been referred to as blindsight, 29 and the navigational vision has been called travel vision. 104 It appears to be a variable but fatiguable function and in our experience may begin to develop in an apparently blind child at about the age of 4 or 5 years.

Learning (Fifth Edition)

Emphasizing research findings and basic concepts, the Interim (5th) Edition surveys the major areas in the psychology of learning from a consistent behavioral point of view. As in previous editions, Learning explores the continuities between human learning and the learning of other animals. The book organizes the phenomena of learning in a systematic way, moving from Behavior Without Learning (evolution) to Learning Without Words (basics in nonhuman behavior and learning) to Learning With Words (human learning and memory). The 5th Edition includes etymological notes at the beginning of each chapter. These capsule word histories are important reminders of how easily our language changes. The glossary summarizes the major terminology of the field and may povide a convenient organizer for study and review.

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Watch the video: ENJOY LIFE ALONE - Jordan Peterson Best Motivational Speech (May 2022).


  1. Kegami

    Well, well ... it will be necessary to take a closer look at this area :)

  2. Tor

    In my opinion it was already considered

  3. Shaktizuru

    Excuse, I have thought and have removed the message

  4. Marleigh

    Develop the topic further. It is interesting to know the details !!!

  5. Binyamin

    Interestingly :)

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