Category: Seeing

A 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.

In the celebrations of the fifty-year forty-year anniversary of the moon landing, we’ve probably all seen this iconic photo of Buzz Aldrin’s footprint on the lunar surface:

Looking at it again yesterday, I realised that there was something that disturbed me about it. The footprint looks wrong somehow. Our world-knowledge tells us that footprints press into the surface they are made on, yet this footprint looks like it rises out. What gives?

The effect is due to a well known visual phenomenon whereby our brains use shading to infer the percepion of shape (in the book, Hack #22). We are wired to assume that light comes from above, so things with shading underneath, like the ridges of the footprint, are seen as sticking out towards us. Things with shading on the top are seen as sticking in, away from us.

You can make the moon-footprint look ‘right’ by turning the photograph the other way up. This is the opposite to the way it is normally shown, but gells with our natural inclination to assume light comes from the top of the photo:

Perhaps the unnatural look of this photo is one source of moonlanding-denial conspiracy theories?

RadioLab has a brilliant short podcast on the psychological role of blinks, based on a study that found that when watching a film our blinks are remarkably synchronised.

The programme dispels the myth that blinking serves only to keep our eyes wet as apparently studies have shown that we don’t blink any more or less in different humidities.

Instead, it explores a fascinating new study that found that blinks became synchronised when watching a film of another person, but not when watching landscapes or listening to stories.

Interestingly, blinks seems to be controlled so they occur at the start and end of meaning actions.

This is from the study abstract:

Synchronized blinks occurred during scenes that required less attention such as at the conclusion of an action, during the absence of the main character, during a long shot and during repeated presentations of a similar scene. In contrast, blink synchronization was not observed when subjects viewed a background video or when they listened to a story read aloud. The results suggest that humans share a mechanism for controlling the timing of blinks that searches for an implicit timing that is appropriate to minimize the chance of losing critical information while viewing a stream of visual events.

Blinking helps us comprehend the world. I find that quite amazing.

We know that blinking is also tied to some quite fundamental functions of the brain. For example, the higher the amount of spontaneous blinking you do, the higher the amount of dopamine you produce in the striatum, a deep brain area.

This is also links to your ability to stop unwanted actions, with a recent study linking higher blink rates to slower stop times.

As always the RadioLab programme is gripping audio velvet. I really recommend some headphones and 15 minutes of undisturbed time to lose yourself.

Link to RadioLab short podcast ‘Blink’.
Link to full text of blink synchronisation study.

‘From Stroboscope to Dream Machine: A History of Flicker-Induced Hallucinations’ is a wonderful article that has just appeared in medical journal European Neurology. It charts how an early finding in visual neuroscience was adopted by the Beat writer William Burroughs and became a fixture of the psychedelic sixties.

Flicker induced hallucinations have been noted throughout history and typically occur when a strong light flashes between 8 and 12hz, also known as the alpha rhythm. They most commonly trigger a type of hallucination called a form constant that comprises of geometric shapes and patterns.

Alpha rhythms have been heavily linked to the function of the occipital lobe and, as we suspect from recent research, ‘inputting’ alpha waves into the visual system via flickers seems to cause hallucinations by knocking a deep brain structure called the thalamus and the occipital lobe out of sync.

As both are part of the visual system, the effect is a bit like knocking a conversation out of sync – misperceptions occur.

Burroughs happened upon the phenomenon and set about creating a machine to produce these hallucinations:

The flicker phenomenon reminded Burroughs of a story he had recently been told by his soul mate Brion Gysin (1916-1986). At the time they both inhabited a cheap hotel in 9, rue Gît Le Coeur, a small alley in the middle of the Latin Quarter of Paris. The place has been known as the Beat Hotel ever since. Gysin was a man with many skills; he was a painter, a poet, a calligrapher, a musician and a cook, all in one lifetime.

On December 21, 1958, as his diary reports, he had been travelling on a bus in southern France. He had fallen asleep, leaning with his head against the window pane. On passing by a row of trees, sunlight came flickering through and Gysin started to hallucinate:

‘an overwhelming flood of intensely bright patterns in supernatural colours exploded behind my eyelids: a multi-dimensional kaleidoscope whirling out through space. The vision stopped abruptly when we left the trees. Was that a vision?’.

Gysin knew by experience what neurophysiologists like Walter were talking about. Burroughs was able to hand him the theoretical framework.

The next step was to manufacture a stroboscope for private use. Gysin persuaded one of his friends, Ian Sommerville (1940-1976), to make one. Sommerville, who was originally a mathematician, came up with a simple but effective design

This was later developed into the commercially produced dreammachine, essentially a light with a rotating slotted lampshade designed to produced flickers in the alpha range. It became popular as both a way of inducing hallucinations on its own and as an aide to hallucinogenic drug trips.

There are plans online from a company who still make the machines to order.

The hallucinations don’t occur in everyone (in fact, I’ve probably spent a few hours of my life in front of a frequency controlled strobe trying to trigger the effect with no luck) and in people with photosensitive epilepsy the flickers can trigger seizures.

The effect is almost unknown in the psychedelic circles circles in which it was once popular, but has now been adopted by neuroscientists wanting a lab-based method to research hallucinations.

If you’re interested in reading more about the whole fascinating story, I can’t recommend the short but fascinating book Chapel of Extreme Experience enough.

Link to full-text of article on flicker hallucinations.
Link to DOI entry for same.

Rather mysteriously, no one can find anyone who has been blind from birth and has later been diagnosed with schizophrenia. I found this interesting snippet from a short article from Behavioral and Brain Sciences:

Five independent searches, varying considerably in scope, methods, and population, failed to identify even one well-defined co-occurrence of total blindness and schizophrenia (Abely & Carton 1967; Chevigny & Braverman 1950; Feierman 1982; Horrobin 1979; Riscalla 1980). We dedicated portions of 2000 and 2001 to e-mail and postal mail surveys of relevant professionals; e-mail and telephone discussions with officials of health, mental health, blindness, and schizophrenia organizations and research institutes; and extensive keyword probes of Medline, PsychINFO, and ScienceDirect databases. Some ambiguity was introduced by very low return rates for our surveys, but the consistent result of all these inquiries was that no instance of totally blind/schizophrenic co-occurrence was found.

The authors give a speculative hypothesis that this is because visual experience during development helps to shape brain pathways heavily reliant on the neurotransmitter glutamate and the NMDA receptor.

It is widely accepted that this system plays a role in the development of psychosis but the idea that it is shaped by visual experience to the point where schizophrenia is impossible is just an interesting idea at the present time.

That’s not to say no-one with schizophrenia is blind (in fact, there are numerous tragic cases of self-blinding) but it is still the case that no-one has yet produced an example of someone who has been blind from birth who later has become psychotic.

If you do hear of anyone, get in touch, contact your nearest cognitive scientist, or if you are a researcher yourself, write up a case study, as it’s an interesting anomaly in the medical literature.

Link to summary of paper on blindness and schizophrenia.

Oliver Sacks has done a wonderful TED talk on hallucinations that has just been released online. He particularly focuses on the hallucinations of Charles Bonnet syndrome where damage or decay of the retina can cause strikingly complex hallucinations of people and animals that seems to be a natural part of the visual scene.

Interestingly, the people affected by the condition are usually well aware that they are hallucinating and remain lucid throughout.

The talk is wonderful and Sacks is engaging as ever, but some of his neuroscience explanation seems a little dodgy.

He discusses the well-known role of an area in the temporal lobes called the fusiform gyrus in face recognition and relates disturbance in this area to face hallucinations:

There’s an area in the anterior part of [the fusiform gyrus] where teeth and eyes are represented and that part of the gyrus is activated when people get the deformed hallucinations [of people with big teeth and eyes].

There is another part of the brain that is especially activated when one sees cartoons. It is activated when one recognises cartoons, when one draws cartoons and when one hallucinates them…

There are other parts of the brain that are involved in the recognition and hallucination of buildings and landscapes.

Actually, all of this seems quite dodgy. I couldn’t find any evidence that part of the fusiform gyrus is specialised for teeth and eyes.

I found one study which linked the viewing of moving mouths or pair of eyes to activation on the superior temporal gyrus, but this is the other side of the temporal lobe. Also, he seems to be suggesting that specific face parts are mapped to specific areas of the fusiform gyrus, again, which I could find no evidence for.

I suspect the bit about specific parts of the brain for buildings, landscapes and cartoons comes from a misunderstanding of neuropsychology experiments as these sorts of pictures are also often used in experiments on face recognition.

One of the big debates in face perception research is whether the fusiform gyrus is dedicated to face recognition or whether it is specialised for any sort of expertise needed for fine grained visual distinction – for example, recognising car types, or birds and so on.

Hence, experiments often will test people on face recognition, but then also on building or drawings so the researchers can find out whether the problem is specific to faces or just a general visual recognition problem. For example, this exact procedure was used in this 2005 study on four people with prosopagnosia, a selective impairment in face recognition.

Apart from maybe a few minor hallucinations from Sacks himself, the talk is excellent and comes highly recommended.

Link to Oliver Sacks TED talk on hallucinations.

ABC Radio National’s Night Air has a wonderfully atmospheric programme on hallucinations, or maybe visual art, or the sensitivity of blindness, or maybe about how the mind constructs reality.

It’s deliciously unfocussed and the programme glides hazily between neuroscience, art, poetry and visual consciousness.

There’s the occasional moment where the vibe slips off its axis, but otherwise it’s just a shear delight to listen to as it mixes artistic and scientific views on the visual.

Link to Night Air programme ‘Visual’

There’s an intriguing study about to be published in Psychological Science finding that people wearing prism glasses that shift everything to the right overestimate the passage of time, while people wearing left-shift glasses underestimate it.

The researchers, led by psychologist Francesca Frassinetti, asked participants to watch a square appear on-screen for varying time periods, and then reproduce the duration or half the duration with a key press.

Glasses that skewed vision to the left seemed to shrink time, while glasses that skew everything to the right expanded it.

Apart from the interesting perceptual effect, it gives further evidence for the idea that our internals model of space and time are heavily linked, to the point where modifying one has a knock-on effect on the other.

In fact, there is increasing evidence that other abstract concepts are implicitly understood as having a spatial layout. Experiments on the SNARC effect have found that numbers seem to have a ‘location’, with larger numbers being on the right and smaller numbers on the left.

At least, that seems to be the case for native English-speakers, but for Arabic speakers, where text is written right-to-left, the reverse seems to be true.

It would be interesting to whether Arabic speakers show a reverse time alteration effect of if they wear prism glasses. Whatever the answer, it would raise lots of interesting questions about how much language influences our abstract ideas and whether it only applies to certain concepts.

Prism glasses have long been a tool in psychology and there is a mountain of research on how we adjust to living in the world even when everything is shifted through the lens.

Tom recently found a fantastic (1950s?) archive film called ‘Living in a Reversed World: Some Experiments on How We See the Directions of Things’ where several volunteers are asked to wear prism glasses for weeks on end.

Hilarity ensues, at least at first, but as co-ordination skills adapt the volunteers can go about their daily tasks, to the point of being able to ride bicycles, even when their vision has been flipped around.

Link to summary of prism and time perception study.
Link to Living in a Reversed World (via @tomstafford)

A remarkable study has just been published in the cognitive science journal Vision Research which may be the first genuine demonstration of brain scan ‘mind reading’.

The study focuses on visual attention and particularly what is called ‘covert visual attention’ – the ability to mentally focus on something without moving your eyes.

For example, take the phrase ‘cat x dog’. I want you to fix your eyes on the ‘x’ and keep them there, but then alter your concentration so you mentally focus on ‘cat’ and then ‘dog’ and back again.

Your eyes aren’t moving but you can concentrate on different things in the scene you’re looking at just by shifting your attention. This is called ‘covert’ visual attention because there is no obvious (‘overt’) bodily movement associated with it, it’s a hidden (‘covert’) mental process.

Since the time of William James, attention has been thought of like a spotlight in that you just ‘shine’ it on an area to make it mentally clearer.

The authors of this new study wondered whether attention was really this selective and decided to use a nifty brain imaging method to test this out.

They relied on the fact that every point in your retina is literally mapped in the brain. Each point in the visual scene has a corresponding area of the visual cortex which is laid out in the same way – in something called a retinotopic map

We know that visual attention selectively boosts activity in the visual cortex, so when you switch between ‘cat’ and ‘dog’ in our example above, the brain increases activity in the visual areas that corresponds to each word.

In other words, it’s possible to measure the effect of visual attention by looking at where changes in visual cortex activity occur.

After doing some tests to make sure they’d verified the exact layout of each of the participant’s retinotopic map, the researchers asked participants in the scanner to systematically focus on specific parts of a circular area cut into segments, with inner, middle and outer rings – all while keeping their eyes fixed in the centre.

They then mapped activity from the visual cortex back into the visual scene to create a ‘heat map’ of where attention was spread.

You can see an example in the image on the right. The ‘x’ never appeared in the actual experiment, I just added those to make the diagram clearer, but they illustrate where the participants were instructed to concentrate.

Overall, the results showed that attention was not tightly focussed like a spotlight. In fact, when we direct our concentration to the outer ring of vision, large areas of the visual scene are flooded with activity.

This happened to a lesser extent with the very inner ring of vision, with visual scene enhancement typically extending outwards as well.

But with the middle ring of vision, the enhancement was pretty tight, being restricted to just that area.

This is an amazing finding in itself, but the ‘mind reading’ part is quite a finale.

The researchers also had a section of their study where they asked the participants to randomly focus on parts of the circle. Remember, they weren’t moving their eyes (and this was checked with a monitor), just changing their internal focus of concentration.

By solely looking at the patterns of brain activation, the researchers worked out where the participants were concentrating with 87% accuracy.

In many previous ‘mind reading’ experiments, researchers have shown people different sorts of pictures and then worked out which ones they were looking at by analysing brain activity.

It’s a largely passive process and relies on distinguishing different physiological reactions. If you measured blood flow to the penis you could probably distinguish whether men were looking at pictures of furniture or people having sex – but you probably wouldn’t call this ‘mind reading’. These previous studies just measured the brain to do something similar.

While such studies are often over-hyped, this new experiment does take the process a step further.

It’s still a very limited task but the participants are voluntarily engaging in a purely internal mental process and the brain scans tell us where their focus of concentration is.

The researchers had no knowledge of where this was beforehand and the same thing couldn’t have been worked out through watching participants’ behaviour.

Link to study.
Link to PubMed entry for same.

The results of the annual visual illusion contest have just been announced and the 2009 winner is a doozy.

Like all the best visual illusions it’s conceptually simple but perceptually striking. In this case a falling ball seems to drop vertically when you look straight at it but seems to glide away at an angle when you see it in your peripheral vision.

Rather nicely, you can switch between the two effects just by looking back and forth. Make sure you click on the ‘Reversal’ button as well for a free-wheeling alternative version.

Visual illusions: the scooby snacks of perceptual psychology.

Link to Visual Illusion Contest website (via @mocost).

Not Exactly Rocket Science discusses the case of a man who experiences the world as a blind man, but who is able to navigate through rooms despite having no conscious visual experience.

TN was a doctor before two successive strokes destroyed his ability to see. The first one severely damaged the occipital lobe on the left side of his brain, which contains the visual cortex. About a month later, a second stroke took out the equivalent area on the right hemisphere [see MRI scan image on the left]. TN is one-of-a-kind, the only known patient with damage like this in the entire medical literature. The fibres that connect the occipital lobes on the right and left halves of the brain have also been severely damaged and tests reveal that no blood flows between these disconnected areas.

Alan Pegna from the University of Bangor in Wales was the first to study TN’s abilities after he was recovering from this second stroke in a Swiss hospital. Pegna was the first to discover TN has an ability called blindsight, that allows him to unconsciously detect things in his environment without any awareness of doing so. He could correctly guess the emotions playing across the faces of other people. And as he did so, his right amygdala – an area of the brain involved in processing emotions – became active.

Blindsight is a condition where, after brain injury, patients lack conscious visual experience but can perform some visual tasks successfully despite thinking they are just guessing.

The first case of blindsight was reported in 1974 by neuropsychologist Larry Weiskrantz, although as with the majority of blindsight cases the patient wasn’t completely blind – in this case it was only for vision on the left hand side.

However, the patient was still able to reliably point to the locations of lights flashed up in the area, despite having no conscious experience of seeing them.

Despite damage to the cortical visual areas in the occipital lobe, it is likely that the earlier subcortical areas, such as the lateral geniculate nucleus (LGN) and the superior colliculus, allow for decision making on the basis of unconscious visual information.

In the new study, the patient is able to use this to avoid obstacles in his path, despite not being conscious of ‘seeing’ them.

This patient has a complete blindness and can complete relatively complex visual tasks without conscious awareness, making him one of the most interesting cases to come to light.

As well as being brilliantly written, the post is illustrated with a video of him avoiding obstacles in a room while walking. Impressive stuff.

Link to NERS post on blindsight case.
Link to study.
Link to DOI entry for same.

The photograph is of some visual illusion paving stones found in Bogot√°’s Zona T this morning. They give the impression of an uneven surface despite being completely flat.

I was in Bogotá to give a talk to the Asociación Colombiana de Psiquiatría Biológica who kindly invited me to their Christmas meeting.

Many thanks to them, and to the town planners of Bogot√°.

Not Exactly Rocket Science has a great write-up of a recent study that may explain why some people are born without the ability to recognise faces – a condition known as congenital prosopagnosia.

Face recognition is particularly associated with a part of the temporal lobe called the fusiform gyrus. Although it’s controversial whether this area is specifically for faces, or is more generally specialised for perceptual expertise of which faces are just the most important example, it’s clear that it is key for understanding faces.

Cibu Thomas from Carnegie Mellon University discovered the problem by focusing on two major white matter tracts that link the fusiform area to other parts of the brain. Both have names that positively trip off the tongue – the inferior longitudinal fasciculus (ILF) and the inferior fronto-occipito fasciculus (IFOF). Thomas studied the tracts using a technique called diffusion tensor imaging (DTI), which measures the flow of water along their length.

The flowing water revealed severe problems with the structural integrity of both white matter tracts in the brains of prosopagnosics. Normal individuals didn’t show any problems, nor did areas of white matter in the prosopagnosics that connected areas completely unrelated to face processing.

In other words, the fibres that connect important perceptual areas in the brain may be much thinner in people who have problems recognising faces.

The image on the left shows the connections between the temporal and the occipital lobes in the participants with the condition and the controls.

As usual, the Not Exactly Rocket Science write-up is clear, concise and engaging, and if you’d like to know a bit more what it’s like to live without recognising faces The Guardian recently published a personal account of day-to-day life from someone with prosopagnosia who can’t even recognise himself in the mirror.

Link to ‘Faulty connections responsible for inherited face-blindness’.
Link to Guardian article ‘I don’t recognise my own face’.

Scientific American has a fantastic gallery of visual illusions images created both by artists and scientists that produce dramatic false motion from still images.

There’s 12 images, but the one pictured is my favourite which is simply described like so: “This illusion is a contemporary variation on the Ouchi pattern, by Kitaoka”.

As with many illusory motion images, they are sometimes more striking if you move your eyes around the images to look at different parts.

Link to illusory motion image gallery (via MeFi).

A brilliant illustration of the Kanizsa triangle made out of kiwi fruit by Flickr user Yves Moreaux.

The Kanizsa triangle is often used to argue that a purely ‘bottom-up’ approach to understanding vision – that says we generate our perception solely from building up from the small details of what we see – is flawed.

In this case, it seems we fill in the outline of the triangle partly based on our prior expectations, because if we follow the contours in the image, there isn’t actually a triangle there.

The triangle illusion is named after the Italian psychologist Gaetano Kanizsa.

Kanizsa was also an accomplished artist who created numerous paintings that played with the concepts of perception.

Link to Yves Moreaux’s brilliant Kanizsa kiwi.
Link to online exchibition of Kanizsa’s paintings.

Firstly, you’ll have to excuse the somewhat ‘in house’ nature of this post, as it’s me writing about Christian writing about Tom. It’s an account of Tom giving an address to the Association for the Teaching of Psychology where he conducted a fantastic demonstration of how you can test out whether your brain adapts to certain visual conditions ‘locally’ on an eye-by-eye basis, or ‘centrally’ in eye independent perceptual brain areas.

Moments into the keynote talk, the teachers and I found ourselves blinded by darkness. As our eyes adjusted, we were told to cover one eye with our hands before the lights were raised again. A little wait for our open eyes to become light-adjusted and then the lights re-dimmed. What would happen to our vision this time? The answer depends on whether adaptation to light levels occurs centrally, in the brain, or locally in each eye. The audience tested this, looking through each eye one at a time and discovering the strange experience of having one eye adapted to the light and one to the dark, thus showing that light adaptation occurs locally. Both eyes open led to a strange, grey, grainy, effect. ‚ÄúWhoever said psychology isn’t useful is wrong,‚Äù Stafford said. ‚ÄúYou now have the perfect strategy for visiting the toilet in the night and finding your way back to your bed in the dark.‚Äù

Light adaptation may well occur locally, but what about adaptation to motion? A huge video of a waterfall filled the screen. After a minute staring at the cascading water, the video was stopped and the audience experienced the well-known illusion of the water appearing to flow upwards. But what if the flowing water was watched with just one eye (with the other covered), with the paused video then observed through the previously covered eye? The illusion was still experienced, thus showing that in this case, adaptation to motion had occurred centrally, in the brain.

If you don’t have a waterfall handy, you may be interested to know it’s a form of ‘motion after effect‘ illusion and there’s a similar demonstration online that you can try. If you go to that link, click ‘detach’ and resize the window to get a bigger version.

You’ll need to supply the room and light yourself though. The hall full of teachers is optional.

Link to BPSRD on visual adaptation.
Link to motion after effect example.