Visual science in the art of Chuck Close

I’ve just found this amazing article on the work of artist Chuck Close from a 2008 edition of the Archives of Ophthalmology.

It examines the visual science behind his pixelated style and how a stroke left the artist paralysed – after which he has produced some of his finest work.

Chuck Close (1940- ) is one of the most famous American artists working today. His distinctive paintings are huge canvases that depict faces, often his own. He works in a nontraditional manner by combining many small geometric forms, usually squares or rectangles, to create a portrait. The individual elements he uses in making an image may be termed pixels. The word pixel is a neologism used in computer technology to mean the smallest form in a digitized image and is a combination of the words picture and element.

Chuck Close is a compelling individual who has endured a great physical misfortune. In 1988 he experienced an occlusion of a spinal artery in the neck, which left him quadriplegic. The occlusion has affected the way he paints, but not his style of painting. Many experts have found it difficult to differentiate work done before the onset of his quadriplegia from that done afterward.

The paintings lead to important questions concerning visual perception and the possibility of artificial vision. What determines our ability to combine many small geometric units into a coherent image? How many different elements are needed to create an image? What are the effects of changing colors within the elements?

Close has had a long interest in science, and even painted a cover for the journal Science.

For someone who paints such remarkable portraits, you might be surprised to learn that he recently revealed he has prosopagnosia, a life-long difficulty in recognising faces.

The Archives of Ophthalmology article looks at how we perceive coherent images from patterns that seem chaotic when viewed at close quarters and how Close takes advantage of these processes in his work.

You can click on the images in the article to see them much larger and really get an idea of how they’re constructed.

Link to Archives of Ophthalmology on Chuck Close and visual science.

The strange-face-in-the-mirror illusion

An intriguing article has just been published in the journal Perception about a never-before-described visual illusion where your own reflection in the mirror seems to become distorted and shifts identity.

To trigger the illusion you need to stare at your own reflection in a dimly lit room. The author, Italian psychologist Giovanni Caputo, describes his set up which seems to reliably trigger the illusion: you need a room lit only by a dim lamp (he suggests a 25W bulb) that is placed behind the sitter, while the participant stares into a large mirror placed about 40 cm in front.

The participant just has to gaze at his or her reflected face within the mirror and usually “after less than a minute, the observer began to perceive the strange-face illusion”.

The set-up was tried out on 50 people, and the effects they describe are quite striking:

At the end of a 10 min session of mirror gazing, the participant was asked to write what he or she saw in the mirror. The descriptions differed greatly across individuals and included: (a) huge deformations of one’s own face (reported by 66% of the fifty participants); (b) a parent’s face with traits changed (18%), of whom 8% were still alive and 10% were deceased; (c) an unknown person (28%); (d) an archetypal face, such as that of an old woman, a child, or a portrait of an ancestor (28%); (e) an animal face such as that of a cat, pig, or lion (18%); (f ) fantastical and monstrous beings (48%).

Caputo suggests that the dramatic effects might be caused by a combination of basic visual distortions affecting the face-specific interpretation system.

The visual system starts to adapt after we receive the same information over time (this is why you can experience visual changes by staring at anything for a long time) but we also have a system that interprets faces very easily.

This is why we can ‘see’ faces in clouds, trees, or even from just two dots and a line. The brain is always ‘looking for faces’ and it is likely that we have a specialised face detection system to allow us to recognise individuals whose faces actually only differ a small amount in statistical terms from other people’s.

According to Caputo’s suggestion, the illusion might be caused by low level fluctuations in the stability of edges, shading and outlines affecting the perceived definition of the face, which gets over-interpreted as ‘someone else’ by the face recognition system.

More mysterious, however, were the participants’ emotional reactions to the changes:

The participants reported that apparition of new faces in the mirror caused sensations of otherness when the new face appeared to be that of another, unknown person or strange `other’ looking at him/her from within or beyond the mirror. All fifty participants experienced some form of this dissociative identity effect, at least for some apparition of strange faces and often reported strong emotional responses in these instances. For example, some observers felt that the `other’ watched them with an enigmatic expression – situation that they found astonishing. Some participants saw a malign expression on the ‘other’ face and became anxious. Other participants felt that the `other’ was smiling or cheerful, and experienced positive emotions in response. The apparition of deceased parents or of archetypal portraits produced feelings of silent query. Apparition of monstrous beings produced fear or disturbance. Dynamic deformations of new faces (like pulsations or shrinking, smiling or grinding) produced an overall sense of inquietude for things out of control.

If any Mind Hacks readers try the illusion out for themselves, I’d be fascinated to hear about your experiences in the comments.

Link to full-text of article.
Link to PubMed entry for study.

An Opthamologist on Mars

Oliver Sacks is interviewed on NeuroTribes where he talks about his forthcoming book and his own experience of spectacular hallucinations that occurred after he developed a tumour behind his retina.

NeuroTribes is a new blog by ace science writer and Wired veteran Steve Silberman. It is part of the new PLoS science blog network and in the inaugural post Silberman has scooped a fascinating interview with the great neurologist and raconteur himself.

Here he discusses how his hallucinations, caused by the brain trying to ‘fill in’ or ‘guess’ what should be in the damaged part of the retina, are affected by smoking pot.

I also had — and still have — almost continuous hallucinations of a low order: geometric things, especially broken letters, some of them like English letters, some like Hebrew letters, some like Greek, some runes, and some a bit like numbers. They tend to have straight lines rather than curves, but they rarely form actual words. This is not something I said in the book, but if I smoke a little pot, they sometimes become words. And they tend to be in black and white — but when I smoke a little pot, they’re in color.

Silberman: That’s wonderful. What do the words say?

Sacks: Short English words of no particular significance like “may,” or pseudo-words, like “ont.” Also, since my back surgery last year, I’ve been on nortriptyline, which is supposed to block the gating mechanism for pain in the spinal cord. I only take a small dose, because it gives me an intensely dry mouth. But even the small dose has a striking effect of enhancing dreams and involuntary imagery, and upgrading my hallucinations from black-and-white to color, and from geometric patterns to faces and landscapes.

The interview is both playful and profound and makes a great teaser for his forthcoming book, which apparently, is due out in October.

Link to Oliver Sacks interview on NeuroTribes.

Distractingly attractive

Driver distractions are a major cause of road accidents. A new study has found that just a simple conversation with someone else in the car can be enough to increase driver errors and that the risk is greater if we fancy the passenger.

The research was conducted in a driving simulator by Cale Whitea and Jeff Caird from the Cognitive Ergonomics Research Laboratory (CERL) at the University of Calgary in Canada where they investigated something called a looked-but-failed-to-see error.

This is a form of change blindness, where we look at a scene but fail to notice something has changed. This is an important source of risk when driving, as we may be going through the motions of scanning the road but not taking in new information.

The study looked at how many of these errors would occur when drivers navigated their way through a simulated city, while also tracking their eye movements and errors with motorbikes and pedestrians on dangerous left-turns.

Crucially, the study compared how people performed when they were alone or with an opposite-sex passenger but also asked them about how attracted they were to the passenger and tested levels of extroversion and anxiety.

The results were striking:

Passenger conversations can be distracting. Higher rates of [looked-but-failed-to-see] LBFTS errors occurred when engaged in conversations with attractive passengers. In particular, those drivers who were most extroverted and attracted to the passenger also tended to be more anxious, drove slower, responded less to the pedestrian, and were involved in a greater number of emergency incidents with the motorcycle.

Considering eye gaze behavior was unaffected, the relationship between these social factors and performance variables suggest the nature of conversational distraction is cognitive. This attentional interference was sufficient in eliciting an eight-fold increase in LBFTS errors involving the motorcycle and four-times more pedestrian incidents.

In other words, conversation did not alter how people looked at the road, but it did affect how many dangerous situations people noticed – they just didn’t take them in. Fancying the passenger meant drivers missed more hazards. Their mind was clearly on other things.

Contrary to what parents might say (‘you were just showing off!’) participants actually drove more slowly when they were attracted to the passenger, but still made more errors.

It’s probably worth noting that it wasn’t the hotness of the passenger which was tested in the experiment, but the attraction of the driver, and that the distracting effect was stronger in women than men.

Link to PubMed entry for study.

Flowers, falling maple leaves and wriggling dwarves

I love this summary of a study on unusual hallucinations in an elderly Japanese lady.

The full article is in Japanese but the translation of the abstract and the form of her hallucinations gives it a stylised quality that reminds me of the traditional art from the country.

The last sentence is wonderfully zen-like.

[Formed visual hallucination after excision of the right temporo parietal cystic meningioma–a case report.]

Brain Nerve. 2010 Aug;62(8):893-7.

Yoshimura M, Uchiyama Y, Kaneko A, Hayashi N, Yamanaka K, Iwai Y.

We report the case of a 64-year-old woman with cystic meningioma; this patients was otherwise healthy and experienced formed visual hallucinations after excision of the tumor. She experienced diplopia associated with metamorphopsia, which had persisted for 5 years only when she laid down and turned on her left side.

After the excision of the convexity meningioma located in the right temporoparietal lobe, she experienced several types of formed visual hallucinations such as closet-like pictures, flowers sketched on stones, falling maple-like leaves, and moving or wriggling dwarves.

She was alert and her visual field was normal; further, she did not experience delirium or seizures. She experienced these hallucinations only when she closed her eyes; these hallucinations persisted for 3 days after the operation.

The patient illustrated her observations with beautiful sketches, and the mechanism of visual hallucinations was studied.

If any of our Japanese readers have access to the article I would love to see if it has examples of the patient’s “beautiful sketches”.

Link to PubMed entry for study.

Dark restaurant alters appetite and eating

We often assume that our appetite depends on how much food we’ve eaten, but a new study conducted in a completely dark restaurant has demonstrated that we don’t feel any more full if secretly slipped extra large portions of food. What we see, it seems, plays a big role in how hungry we feel.

The research, led by psychologist Benjamin Scheibehenne and published in the journal Appetite, invited participants to have lunch in a restaurant in downtown Berlin.

While the entrance bar was lit, the restaurant itself was pitch black and the volunteer ‘customers’ were served by blind waiters and waitresses who were capable of working in the dark.

The ‘customers’ ate two main courses in the dark dining area, but what they didn’t know, was that half were served normal-sized portions while the other half were served super-size portions that were more than a third bigger.

Afterwards, the light was switched on and they were offered a dessert that they could serve themselves.

The researchers measured how much dessert each person ate and the diners were asked to fill in a questionnaire where they estimated how hungry they were, how much they ate and whether they liked the food.

Exactly the same experiment was run a few weeks later, with different volunteers, but with everyone eating in the light, as in a normal restaurant.

For those who could see what they were eating, the size of their main course had a big effect on how full the diners felt and how much dessert they ate afterwards. But for those who dined in the dark, portion size didn’t seem to make a difference.

In other words, people were experiencing fullness based as much on their visual estimation of how much food they were eating as their actual physical consumption. Eating without seeing means we unwittingly eat more and feel less hungry.

This chimes was a 2005 study, where a research team created soup bowls that secretly refilled for some of the diners to the point where they ate three quarters more soup than others.

Despite this, those diners with the ‘bottomless soup bowls’ did not believe they had eaten more, nor did they feel themselves as more full than those eating from regular bowls.

The researchers from the Berlin study note that these findings show the importance of context for healthy eating and make an interesting point about how something as common as eating in front of the TV may affect how much we eat, simply by affecting how much we focus on our food.

Link to PubMed entry for study.

Purple haze: paint huffing hallucinations differ by hue

Photo by tanakawho. Click for sourceAdolescent solvent abusers reported that different colours of paint cause different types of hallucinations, according to a remarkable study just published in Drug and Alcohol Review.

The research, led by Michael Takagi from the University of Melbourne, was only a small study of 16 young people who sniffed spray paints, but the results are quite striking.

Although all users reported similar levels of pleasure, all those who preferred chrome paint (gold, chrome and silver) reported they used it for the vivid, detailed visual and auditory hallucinations while those who preferred non-chrome paint rarely experienced changes in perception.

The briefly described experiences are as heartbreaking as they are curious:

For example, one young inhalant user had been removed from her home and placed in residential care. She found the situation difficult and did not assimilate well with her housemates, who had also been removed from their homes. Every day, she would go behind the fence of her residential unit and sniff CP [chrome paint]. She reported that faces would appear out of the wooden fence and talk with her, and she felt that these were her only friends. In contrast, another young inhalant user particularly enjoyed playing video games that were available in his residential unit. However, he was only allowed to play for specific amount of time each day. After sniffing CP, he would hallucinate that he was the hero of the video game.

Furthermore, all of the chrome paint users reported that the hallucinations they experienced differed between colours, whereas only a third of the non-chrome paint users said this was the case.

The study didn’t enquire exactly how the experiences differed between colours, and it can’t say how much the differing reported effects are due to different paint ingredients or simply due to their psychological associations, as it was just a survey of effects.

Link to study summary on PubMed.

Missing the big picture in the faces of others

Image from Wikipedia. Click for sourceRadioLab has an interesting discussion between neurologist Oliver Sacks and artist Chuck Close about their experience of having prosopagnosia – the inability to recognise people by their faces.

The condition is often called ‘face blindness’ but the discussion gives a great illustration of why the label is so inaccurate because Chuck Close is famous for his detailed and evocative portraits of people’s faces.

At this point, it’s worth saying that there are various forms of prosopagnosia, an acquired version which people get after brain damage, and an inherited form, which Oliver Sacks and Chuck Close have.

You can see Close’s portraits online but you really need to see them in real life to experience their impact because they are typically huge (2-3 metres high) and incredibly detailed.

This shows that prosopagnosia is clearly not ‘face blindness’ – people with the condition can see faces fine – what they can’t do is distinguish people by their facial features. Faces just seem all the same – in the same way that you or I might have trouble distinguishing sheep by their faces.

We know a significant part of the difficulty is making sense of the structure of faces rather than their details. Statistically, human faces are very similar, and we have developed a way of perceiving faces that includes their overall layout.

You can demonstrate this process in action by simply by turning faces upside-down and showing that our ability to pick out differences is suddenly markedly reduced.

The Thatcher effect is probably the most striking example of this where changes to the eye and mouth seem hideous when the face is the right way up but when inverted we struggle to notice them.

This is because upright faces engage our perception of face structure into which the details are integrated. With upside-down faces we’re left having to do piecemeal feature-by-feature comparisons like a newspaper ‘spot the difference’ competition.

Music is a good analogy. If you heard sequences of disordered musical notes, some of which were identical and some of which had just one note different, you’d probably struggle to say which sequences were the same or different than the ones before.

But if you heard songs, some of which were identical and some of which had a single bum note, you’d easily pick out which were different because our understanding of the structure of melody makes discordant sounds stick out like a sore thumb.

Normal face perception is just picking up on the melody of faces while people with prosopagnosia generally lack this ability (although to different degrees).

In the RadioLab interview, Chuck Close says he paints faces by taking a photo, dividing it up into squares and then painting the canvas detail by detail.

In other words, he’s probably doing something similar to how he perceives faces. In fact, we might guess that Close’s prosopagnosia has given him a focus on detail which facilitates his striking portraits.

By the way, Chuck Close is a generally amazing guy and in 1988 suffered a stroke which left him partially paralysed and without the ability to coordinate his hands to paint such fine detail. Instead, he’s turned to painting portraits which are almost impressionist.

For each section of detail he paints the general pattern of light. Up close the paintings look incredibly abstract but when you step back they merge to form, amazingly, incredibly life-like face portraits.

Link to RadioLab on prosopagnosia.

Hallucinating the void

Rhode Island Medical News recently published an April fools article where the author joked about negative hallucinations, where someone didn’t see things that were really there, seemingly unaware that such hallucinations are in fact possible.

The article, which you can read online as a pdf, has various humorous references to jumping traffics lights or ignoring family members. But when I’m talking about the genuine version I don’t mean lapses of attention, blind spots, inattentional blindness or other momentary failure-to-notice effects. I’m talking about not seeing specific barn door obvious objects in your field of vision when you are concentrating on the area.

These are genuinely called negative hallucinations in the scientific literature although, as far as I know, they only occur in one specific context – after hypnosis.

In fact, the induction of a negative hallucination forms part of the Stanford Hypnotic Susceptibility Scale (Form C) although these sort of ‘anti-hallucinations’ are only experienced by the most hypnotisable of people – as are most ‘cognitive’ suggestions that effect the experience of your own mind (rather than changes in the sensation of control of movement, which most people can experience something of).

There is a small literature on ‘negative hallucinations’ with several studies examining changes in electrical activity from the brain (‘evoked potentials’) as the hallucination becomes active.

It’s still not clear how negative hallucinations work exactly. Almost all studies have found changes to attention, our ability to selectively process perceptual information, although the data is inconsistent largely owing to the small number of studies – a constant bugbear of hypnosis research.

Link to April fools article PubMed entry.
pdf of full-text
Link to Google Scholar search of negative hallucination studies.
Link to PubMed search of negative hallucination studies.

Visual acuity improves by autopilot

Photo by Flickr user MATEUS_27:24&25. Click for sourceWe tend to assume that visual acuity, the ability to distinguish fine detail with our eyes, is a physical limit of the body but a new study just published online by Psychological Science shows that prompting people with ideas about people who have excellent eyesight actually improves clearness of vision.

The research was led by psychologist Ellen Langer who has become well-known for her inventive and counter-intuitive research that has shown how changing beliefs and mental attitude can affect our performance.

Here’s the abstract of the study which describes the results of the main experiments:

These experiments show that vision can be improved by manipulating mind-sets. In Study 1, participants were primed with the mind-set that pilots have excellent vision. Vision improved for participants who experientially became pilots (by flying a realistic flight simulator) compared with control participants (who performed the same task in an ostensibly broken flight simulator). Participants in an eye-exercise condition (primed with the mind-set that improvement occurs with practice) and a motivation condition (primed with the mind-set “try and you will succeed”) demonstrated visual improvement relative to the control group. In Study 2, participants were primed with the mind-set that athletes have better vision than nonathletes. Controlling for arousal, doing jumping jacks resulted in greater visual acuity than skipping (perceived to be a less athletic activity than jumping jacks). Study 3 took advantage of the mind-set primed by the traditional eye chart: Because letters get progressively smaller on successive lines, people expect that they will be able to read the first few lines only. When participants viewed a reversed chart and a shifted chart, they were able to see letters they could not see before. Thus, mind-set manipulation can counteract physiological limits imposed on vision.

It’s worth saying that Langer and her team interpret the results in terms of ‘mindfulness’ but use a somewhat idiosyncratic definition of the term where most people would just describe it as priming or expectancy – that is, being exposed to a concept or having a certain approach encouraged by the circumstances.

The psychological concept of mindfulness is more commonly used to refer to an attentive awareness of experience that acknowledges each thought or perception but doesn’t get caught up or involved in it.

It is drawn from the Buddhist meditation practice of the same name and has become of interest to psychologists for treating intrusive thoughts and sensations and there is now increasing evidence for its effectiveness.

Despite this, Langer’s study is in line with previous experiments that have shown that exposing people to a stereotype subtly shifts their behaviour to more closely match the stereotype.

For example, studies have found that people’s performance on a quiz could be improved by asking them to think about the lifestyle of a professor and made worse by asking them to think about supermodels or football hooligans.

Another found that participants who were exposed to ideas about old people walked more slowly afterwards.

Interestingly, this effects seems only to hold true for general stereotypes as when people are primed with specific extreme examples (such as Albert Einstein instead of ‘professor’, or Kate Moss instead of ‘supermodel’) exactly the opposite happens, likely because instead of triggering a general association it leads us to make a direct personal comparison with the individual which may affect our motivation, whether we realise it or not.

Link to full text of Langer study.

In the Exploratorium’s distorted room

The San Francisco Exploratorium is the Mind Hacks of science museums – every exhibit is hands on, giving you the chance to experiment with and experience for yourself scientific principles.

Obviously, one of my favourite exhibits was a psychology demonstration, one based on a classic visual illusion known as the “Ames’ Room”. We’ve a small model of this in Sheffield, which I use when teaching PSY101, but the Exploratorium’s “distorted room” is full size demonstration of the effect. Here’s me and a friend in the room:

Notice anything odd? We’re the same size in reality, but I (on the right) look significantly larger.

The illusion takes advantage of the unavoidable principle that size and distance are confounded – known as “Emmert’s Law“. It is Emmert’s Law that means that big things far away can look the same size as small things near by. Our brain makes assumptions about how far away things are and uses these to inform our impression of size. The distorted room is built so that, from one perspective only, the two sides of the room look an equal distance away. In fact, the corner on the right is far closer to the viewer (the camera in this case) than the corner on the left. Because I really am nearer the camera I make a larger image on the retina (take up more pixels on the camera), but because the brain assumes that I am the same distance away as my friend on the left the only conclusion that my visual system can draw is that I must be much larger than him.

Normally your visual system isn’t fooled about depth – clues in the scene, the difference between the image on your two eyes and movements of your head can all help reveal how far away different parts of the scene are. The distorted room removes some of these clues by forcing you took look at the room with one eye from a fixed point, and other clues it deliberately tricks (like the shape of tiles on the floor, which look the same from left to right, but actually get smaller, because the tiles on the right are closer).

The confounding of size and distance is the same principle behind illusions like this:


The effect only works because it is in a photograph (so from one perspective) and because the relatively featureless desert removes other clues to the depth of objects.

So the next time you close one eye and line up someone in the distance between your thumb and forefinger while muttering “I’m crushing your head!“, think of Emmert’s Law. And if you are in San Francisco, visit the Exploratorium!

Clearing the fog of vision

Neuroscientist Pawan Sinha gave an inspiring talk to TED India about his work on providing treatment for visual problems and how this is over-turning many of our long-standing assumptions about how the brain develops the ability to make sense of the visual world.

Sinha focuses on children and adults who have grown up with congenital cataracts – a clouding of the eye’s lens that prevents light from entering the eye.

In essence, it’s like growing up with a blindfold on or while wearing very clouded glasses. The condition is easy to treat with minor surgery but removing the cataract ‘blindfold’ after childhood doesn’t give the personal normal vision.

This is because we are not born ‘seeing’ like we do in later childhood, the brain learns to do so in the early years of life through having experience of the visual world. For example, being able to separate objects from their background is something the brain learns to do – so we can tell that there is a postbox in front of the wall and not that there is a wall with a picture of a postbox on its surface.

Without this experience the visual system doesn’t acquire these abilities and so people who have cataracts removed later in life typically do not have normal vision – despite their eyes being restored to full function.

It was thought if cataracts were removed in late childhood the person would be stuck with missing visual skills, even though their sight would improve in some areas. However, Sinha and has team published an important study in 2006 on a woman who had cataracts removed at the age of 12, well past the time where vision was assumed to be salvageable, but who had near normal vision twenty years after her surgery.

This suggested to the research team that visual development can happen later in life and wasn’t fixed in the early years, as had been assumed from animal studies or from assessments of patients that had only happened shortly after surgery.

Sinha runs Project Prakash that provides cataract surgery to people in India but this has also allowed him the opportunity to study visual development in more detail and his TED talk is on how is combining both the humanitarian and scientific mission to expand our understanding of the visual brain and advance treatments for visual problems.

Link to Pawan Sinha’s TED India talk.
Link to Project Prakash website.

Hallucinating reality’s wallpaper

Photo by Flickr user mike138. Click for sourceHallucinations usually appear as illusory objects on the normal background of reality, but an interesting case report in the medical journal Movement Disorders reports a case of someone who hallucinated background scenery on which real people were superimposed.

We describe a patient with PD [Parkinson’s disease], who had unusual background scenery VHs [visual hallucinations] on which a true person was superimposed…

In December 2008, when her husband died, she experienced background scenery VHs appearing in the left upper part of her visual fields. The abnormal scenery often became larger to encompass the full visual fields and always comprised the countryside where she was born and grew up….

In July 2009, she spoke to her deceased husband in the medical examination room, and she experienced a background scenery VHs during the examination. A physician requested her to draw the VH, and she drew a countryside scene, appearing sad. When asked how a physician in front of her was reflected in her visual field, she replied that the physician appeared normal but beside a river in the midst of the VH.

Link to PubMed entry for brief case report.

Does squinting really improve vision?

Photo by Flickr user massdistraction. Click for sourceScience radio show Quirks and Quarks had a fascinating segment on its most recent programme asking whether squinting really does help you see more clearly. It turns out, it does.

The programme talks to ophthalmologist Stephanie Baxter from Queen’s University in Kingston who notes that squinting focuses the incoming light onto the fovea – a central point on the retina responsible for sharp central vision – and cuts out light from other directions.

The short segment on squinting is at the bottom of the page.

Link to December 5th edition of Quirks and Quarks.

Do blind people hallucinate on LSD?

I’ve just found a remarkable 1963 study [pdf] from the Archives of Opthalmology in which 24 blind participants took LSD to see if they could experience visual hallucinations.

It turns out, they can, although this seems largely to be the case in blind people who had several years of sight to begin with, but who later lost their vision.

Those blind from a very early age (younger than two years-old) did not report visual hallucinations, probably because they never had enough visual experience to shape a fully-functioning visual system when their brain was still developing.

It is evident that a normal retina is not needed for the occurrence of LSD-induced visual experiences. These visual experiences do not seem to differ from the hallucinations reported by normal subjects after LSD.

Such phenomena occurred only in blind subjects who reported prior visual activity. The drug increased the frequency of visual events such as spots, lights, dots, and flickers. However, the complex visual experiences reported by 3 subjects after LSD did not occur after placebo or in ordinary experience.

It is interesting to note that duration of blindness was not related to the occurrence of visual hallucinations; nor was intelligence, acuity of visual memory, or use of visual imagery in speech.

I mentioned in an earlier post on auditory hallucinations in deaf people that I’d heard rumours of studies on LSD in blind people but never found any reports. This study is not the only one it seems. The paper reviews several other studies in the same area.

Three other reports deal with the effects of hallucinogenic drugs on blind subjects. Alema reported that 50 micrograms of orally administered LSD induced elaborate visual hallucinations in a subject with bilateral enucleations of the eyeball. However, the effects of 50 micrograms of LSD are stated to have persisted for the incredibly long period of 5 days (they usually last 6 hours). This subject was noted to have spontaneous visual activity.

Zador administered mescaline orally in doses of 0.05 to 0.4gm to 10 blind subjects. Elaborate visual hallucinations usually followed. Most of the subjects had prior spontaneous visual activity, but it is difficult to evaluate this activity because they also had central nervous system diseases. The presence or absence of light perception was not specified for this group, and no control studies were carried out.

Forrer and Goldnerr gave LSD, 1 microgram per kilogram to 2 blind volunteers, both of whom had suffered destruction of the optic nerves. Neither reported visual hallucinations, no mention was made of prior spontaneous hallucinations, and no mention was made of prior spontaneous visual activity.

pdf of full text of study.
Link to PubMed entry for study.

Visual illusions can be caused by imagination

Photo by Flickr user Arnar Valdimarsson. Click for sourceA fantastic study just published in Cognition reports that the motion aftereffect illusion, where staring at something constantly moving in one direction causes illusory movement in the opposite direction when you look away, can be caused just by imagining that the movement is happening.

The effect is occasionally called the ‘waterfall illusion’ because it can be triggered by staring at a waterfall for a few minutes and then looking at the nearby bank, which will seem as if it is moving upward, in the opposite direction to the falling water.

It was traditionally explained by the fact that direction-specific motion-detecting neurons in the brain’s visual areas ‘habituate’ or adapt to constant movement by slowly becoming less active, as if they barely need to keep reporting with the same vigour because they’re just detecting more of the same.

According to this explanation, when you look away, these ‘habituated’ neurons are caught off guard and the neurons that look out for motion in the opposite direction are relatively stronger and so, until the balance is readdressed, give the impression that the world is moving contrary to your past experience.

As with most of these things, it turns out not to be quite so simple, but the effect is so easily invoked that it is used widely in vision and motion research.

One of the key findings in this area is that visual imagery activates some of the same areas as actually seeing what you’re thinking of. In other words, the brain seems to simulate the visual experience actually in the visual system.

Or at least, that’s what it looks like from the brain scans, but just because the same areas are active during both tasks, it doesn’t mean the same neurons are being used. It could be completely different processes at work that just happen to share the same neural office space.

So here’s the cool bit. This new study, led by psychologist Jonathan Winawer, asked participants to briefly view a moving pattern. It only appeared briefly, not long enough to cause the effect, and then disappeared.

Then were then shown the same pattern, without any movement, and were asked to imagine that it was moving in the same way. After a short while, the pattern was replaced by a picture of motionless dots, and they were asked to indicate if they saw the dots moving in a particular direction.

If the effect appeared, participants should see the dots moving in the opposite direction.

The participants were asked to imagine different directions and types of motion and then were given the same task but where they didn’t need to imagine anything, as the pattern moved by itself.

As expected, the moving pattern caused a clear motion aftereffect, but rather wonderfully, the effect appeared after participants had simply imagined the movement. It wasn’t as strong but it was clearly there.

They researchers also asked the participants after which direction would they expect the dots to go in, to check they hadn’t heard about the effect or were just doing what they thought was expected of them, and they couldn’t reliably give the correct direction that the effect would cause.

This provides good evidence that when imagine visual experiences we’re actually running a simulation in the same parts of the brain that are used to actually see the world.

Link to PubMed entry for study.
pdf of full text paper.