August 25, 2008

Kanizsa kiwi:

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.

—Vaughan.

July 28, 2008

Waterfalls, adaptation and light:

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. “Whoever said psychology isn't useful is wrong,” Stafford said. “You now have the perfect strategy for visiting the toilet in the night and finding your way back to your bed in the dark.”

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.

—Vaughan.

July 22, 2008

Through the looking glass:

The New York Times has a great article on the psychology of mirrors that shows that they're both cognitively challenging and have the power to change our social behaviour.

As a kid I spent hours puzzling over the fact that mirrors seemed to swap left and right but not up and down and it seems that there's much about mirrors that we just don't get very easily - such as judging how big our reflection will be. As it turns out, it's always half our size.

Another curious aspect is that simply the presence of a mirror in a room changes our social behaviour because it seems to make us more self-aware.

Other researchers have determined that mirrors can subtly affect human behavior, often in surprisingly positive ways. Subjects tested in a room with a mirror have been found to work harder, to be more helpful and to be less inclined to cheat, compared with control groups performing the same exercises in nonmirrored settings. Reporting in the Journal of Personality and Social Psychology, C. Neil Macrae, Galen V. Bodenhausen and Alan B. Milne found that people in a room with a mirror were comparatively less likely to judge others based on social stereotypes about, for example, sex, race or religion.

“When people are made to be self-aware, they are likelier to stop and think about what they are doing,” Dr. Bodenhausen said. “A byproduct of that awareness may be a shift away from acting on autopilot toward more desirable ways of behaving.” Physical self-reflection, in other words, encourages philosophical self-reflection, a crash course in the Socratic notion that you cannot know or appreciate others until you know yourself.

Unfortunately, the article misses out one of the most fascinating scientific findings - the fact that our understanding of mirrors can be selectively impaired after brain injury.

It's called mirror agnosia and is a condition where people lose their sense of reflection.

In these cases, the patient still has intact knowledge about mirrors, they can describe what they do and how they work, but they can't seem to put it into practice.

For example, the patient stands in front of a mirror and the researcher holds a pen over the patient's shoulder and asks him to reach for it. Most people would reach backwards, people with mirror agnosia reach forwards and bang their hand into the glass.

In this study, the researchers noted that "all four patients kept complaining that the object was 'in the mirror', 'outside my reach' or 'behind the mirror'. Thus, even the patients' ability to make simple logical inferences about mirrors has been selectively warped to accommodate the strange new sensory world that they now inhabit".

Even more curious are cases of mirrored-self misidentification, a delusional variant where patients look into the mirror, see themselves, and believe it is another person.

Here's a case description from a 2001 study of a patient with the condition:

TH described his reflection as a person who was a 'dead ringer' for himself. TH frequently attempted to talk to the person, and said that as the person never replied he could only assume he had something wrong with his voice or tongue. When asked what he thought the person's personality was like, TH replied that the person had not given him any reason to be suspicious. Asked where the person lived, TH said he lived in an apartment adjoining TH's own apartment (although there was no other apartment on that block of land).

Link to NYT article 'Mirrors Don’t Lie. Mislead? Oh, Yes'

—Vaughan.

July 15, 2008

Visual cliff hanger:

Vimeo has some video of what looks like footage from Gibson and Walk's original 1960 'visual cliff' experiment where they tested whether infants had depth perception by attempting to get them to walk over glass plates suspended above a drop.

Unfortunately, the video doesn't fully describe the experiment, which is a pity as it was a fantastic idea.

The researchers wanted to find out whether 6 to 14 month-old infants could perceive depth. Babies are not the best conversationalists, but they do have a natural sense of danger, so the experiment is based on the idea that the babies will avoid perceived danger, even if it's completely safe.

The study put the infants, one at a time, in the middle of a table, with one side replaced by glass so you could see the 'drop'.

Their mothers would try and tempt them over both sides, and if the kids had no depth perception, the glass 'drop' wouldn't seem scary and they'd just walk straight over. Those who could see the 'drop' would avoid it.

Pretty much none of the infants wanted to walk across the 'visual cliff', suggesting that even kids of 6 months old could perceive depth.

Children younger than that generally can't crawl though, so it makes it a bit harder finding out at what age depth perception develops.

In 1973, a study by psychologist Andrew Schwartz placed five and nine-month olds on each side of the 'visual cliff' and measured their heart rate.

When placed over the glass 'drop', the five month olds typically showed no increase in heart rate, suggesting there was no danger response. This suggests depth perception probably kicks in between about five and six months old.

More recent research has shown it's a more complex picture than this, as depth perception has many parts which don't all seem to develop at the same rate, but the 'visual cliff' experiment is still widely used in psychology.

Link to video of 'visual cliff' experiment.
Link to text of original study.

—Vaughan.

June 14, 2008

Best visual illusion of the year announced:

Mixing Memory has alerted me to the fact that the winner of the Best Visual Illusion of the Year Contest has been announced, and what a fantastic illusion it is.

It's an animated one, so you need to go to the page and stare at the dot in the centre for 20-30 seconds.

The creators of the winning illusion, psychologists Rob van Lier and Mark Vergeer, have put up a pdf with their explanation of the effect.

And if you're still illusion hungry after that, you can check out the rest of the finalists that came in the top 10.

On a related note, Scientific American have recently released one of their 'special editions' that collects V.R Ramachandran and Diane Rogers Ramachandran's monthly articles on illusions into one magazine. I got mine from a newsagent but you can also purchase it as a DRM-free pdf online for $4.95.

Link to Top 10 2008 contest winners.
Link to Mixing Memory's take on the winner.

—Vaughan.

February 04, 2008

A blind man hallucinating:

NPR has an brief but interesting piece on a blind man who has visual hallucinations.

Stewart, the person in question, lost his sight due to hereditary sight-loss, but has developed Charles Bonnet syndrome, a curious condition where playful visual hallucinations are common.

Two things about this condition are striking: firstly, the hallucinations are typically complex and intricate but the damage is typically only to the retina, the cortex remains intact.

Secondly, unlike many other conditions where hallucinations are common, the person typically retains complete insight. They know they are hallucinating and typically don't mistake hallucinations for the real world.

While the person interviewed in this radio segment is blind, Charles Bonnet syndrome can occur in people with partial sight, who may have only lost vision in one part of their visual field (often due to macular degeneration). In these cases, even when the hallucinations can 'blend in' with true vision, the person usually knows the difference.

One of the most remarkable things about the interview is that the Stewart's hallucinations can be triggered by quite idiosyncratic things (such as foods and thoughts) and that he takes such joy in the experience.

If you want to read more about the syndrome, the Fortean Times published a great article on it back in 2004.

Link to NPR segment on Charles Bonnet syndrome.
Link to FT article on the same.

—Vaughan.

January 28, 2008

Polanski and the Professor:

It was 1970, and a white Rolls Royce was gliding through the streets of London. Inside were the obviously disturbed Roman Polanski, the film director still reeling from the murder of his wife, and Richard Gregory, the legendary cognitive psychologist.

Polanski had discovered Gregory's work on visual perception through his book Eye and Brain and decided he wanted to enlist Gregory's help to create a 3D horror movie.

The movie was intended to be revolutionary, taking advantage of the brain's perceptual quirks to make a truly disturbing visual experience.

They spent the week in Polanski's office, actually the rear of his white Rolls Royce, discussing concepts, checking out studios and making plans.

In the end, their plans were too ambitious and were abandoned by Polanksi, who moved on to other projects.

Gregory remembers the episode well however, and discusses his meeting with Polanski, and the science behind their abandoned project, in an online audio recording.

Interestingly, Gregory also mentions that Polanksi also wanted to use the techniques they developed to make a 3D erotic movie.

Visual perception lectures would have never been the same again, much to the delight of generations of psychology students, but sadly, it remains only as a wonderful tale of an unlikely pairing.

The recording seems to be from a fantastic Polanski DVD box set that also contains his film Repulsion, notable for its portrayal of a young woman's descent into a terrifying psychosis and the film's use of perceptual distortion to communicate the experience to the viewer.

Link to audio of Gregory discussing his collaboration with Polanski.

—Vaughan.

December 26, 2007

Pulsing visual illusion:

Omni Brain has found an op-art style visual illusion that seems to pulse out from the centre.

Click on the link below or on the image to get the full picture, and if you don't see the effect straight away, just glance at the corners.

The effect is a slow shimmering movement when it kicks in.

Link to pulsing visual illusion.

—Vaughan.

November 27, 2007

Mind snacks:

Exploratorium has a gallery of try-it-yourself perception experiments. There's plenty of great material here, not least because of the the slightly bizarre photos of people with distracting 80s haircuts.

There are quick projects on everything from proprioception to taste, and you can tell which are the good ones because they list 'adult help' as one of the materials.

Think of it as the Mind Hacks that time forgot.

Link to groovy gallery of Exploratorium perception 'snacks'.

—Vaughan.

October 24, 2007

The beauty of false depth:

The image is one of many beautiful street art images from artist and architect Kurt Wenner who uses false perspective to give the images an impression of a 3D structure when viewed from a certain angle.

Wenner uses the same optical manipulation as Julian Beever, whose work we covered previously on Mind Hacks.

It takes advantage of the fact that we use visual features such as relative sizes to infer the depths of objects in the visual field.

When this is manipulated, we can be fooled into thinking that a depth is present in spatial dimensions where it can't possibly exist - like in this case, where it seems as if the paintings represent 'holes' in the floor.

However, because in reality, these are flat images, the effect is lost when viewed from an alternative angle.

There are many more stunning images on Wenner's website.

Link to Kurt Wenner's street art portfolio (thanks Ceny!).
Link to previous post on Julian Beever's optical street art.

—Vaughan.

Strobing numbers show saccadic vision:

This week's New Scientist has a brief letter which describes an elegant demonstration of visual processing during eye movements.

When you move your eyes (known as a saccade), visual input is suppressed, so less information is processed by the brain during the move.

This can be easily demonstrated, as described in one of the hacks in the Mind Hacks book (pdf).

An earlier article in New Scientist suggested that visual perception shuts down completely during the move, and someone wrote in with an elegant demonstration to show that this isn't the case.

It is not strictly true that your visual perception mechanism shuts down completely during a rapid eye movement (22 September, p 34). This can easily be confirmed by flicking your eyes across a digital clock running off an alternating-current power supply, whose figures are luminous and flash at 100 or 120 hertz. You may see a line of images of the numbers, spaced out in proportion to the speed of your eye movement.

The same applies to a TV image: flicking your eyes to the right or left produces a succession of lozenge-shaped images, whereas flicking up or down results in a series of images respectively drawn out or squashed. If you flick your eyes down fast enough you can reduce the picture to a single bar, and if you flick your head down at the same time you can even manage to invert the picture, though you have to be very quick. Do not attempt this, however, if anyone is watching you.

Link to NewSci letter 'Saccade effects'.
pdf of hack to demonstrate visual suppression during saccade.

—Vaughan.

October 04, 2007

Artificial intelligence 'sees' visual illusion:

A study just published in PLoS Computational Biology has reported that an artificial intelligence system trained to make sense of a simulated natural environment is susceptible to some of the same visual illusions that humans fall for.

In one of these, the 'Herman grid' illusion - illustrated on the right, you may be able to 'see' fuzzy patches of grey in the white stripes, despite the fact that there is no grey in the image (click for a bigger version if it's not clear).

David Corney and Beau Lotto, researchers working in the Lotto Lab (which has a wonderful website by the way), have been training artificial intelligence systems to distinguish surfaces in a simulated natural environment with lots of 'dead leaf'-like shapes.

When training these sorts of systems, the idea is not to program them with specific rules, but to present an image and let the neural network make a guess.

The researchers then 'tell' the AI system whether it is correct in its guess, and it adjusts itself to try and reduce the extent of the error on the next guess. After many learning trials, these sorts of 'back propagation' neural networks can make distinctions between quite complex stimuli.

In this case, Corney and Lotto decided that once the system was fully trained to complete its task successfully, they would test it with some visual illusions experienced by humans.

Interestingly, the AI system was susceptible to the Herman Grid illusion, sensing 'grey' where there was none. Other illusions produced similar results.

The fact that both humans and AI system 'fall' for the same illusions, suggests that they take advantage of visual abilities that have been shaped by our experience of the visual world.

Link to paper in PLoS Computational Biology (thanks Matt!).
Link to study write-up from the university's news site.
Link to Lotto Lab website (with loads of cool images and demos).

—Vaughan.

October 01, 2007

Illusory motion with waves of almonds:

I've just found a visual illusion that gives a striking impression of motion from a static image. It's entitled 'this picture is not animated', which, like anything eye-catching on the internet, immediately made me check whether it was or not.

With many of these sorts of illusory motion images, you can 'stop' the motion by simplying viewing them through a very small aperture.

Putting a pin through a piece of paper and viewing it through the hole does the trick, but so does making a small viewing hole with your fingers.

As you can see yourself, the picture stops 'moving' when viewed like this, but starts again as soon as you view it normally.

This also prevents stars from twinkling when you view them at night. The traditional explanation of 'star twinkle' is that the light gets bounced around as it travels through the atmosphere, giving it the twinkling effect.

In fact, by looking at them through a small hole, you're preventing any effects caused by your eyes moving about.

The fact that the illusion stops moving and the stars stop twinkling when you do this, suggests that the way our eyes scan across the visual scene is an important part of why we see the false movement in these sorts of images.

Because of this, you can 'speed up' and 'slow down' the false movement in the visual illusions by changing how often you move your eyes.

UPDATE: Thanks to celeriac for posting a link to a scientific paper which explains this effect.

Link to striking movement illusion.

—Vaughan.

August 25, 2007

Pink slip, feeling blue:

Ben Goldacre over at Bad Science has written a great analysis of a recent study that suggested we have the traditional 'pink for girls, blue for boys' because of evolutionary differences in colour preference.

However, it seems not only are the study's findings not strong enough to make an evolutionary claim, but that the 'pink for girls, blue for boys' idea is relatively recent and hardly as traditional as we like to think.

The data itself is interesting if not a little unspectacular. Men and women from the UK showed different colour preference curves with men showing a preference for bluer shades over women.

In a sample of Chinese participants the preference was much less pronounced and peaked at more redder shades overall.

One of the curses of evolutionary psychology, the science that attempts to work out whether any of our psychological preferences are the result of natural or sexual selection, is that any sex difference is fodder for an evolutionary explanation.

Actually, we know there are definite differences in colour perception between men and women. There's a great paper that summarises the scientific evidence which available online as a pdf.

There are sex-linked differences in specific genes that are linked to colour perception, which is why men are more likely to be colour blind and perhaps 1% of women may have four, rather than three, colour receptors in the retina.

But as Ben points out, simply finding a sex difference in colour preference really doesn't tell us anything about genetics or evolution. It could easily just be an effect of culture or fashion.

Link to Bad Science on pink-blue study.
pdf of paper on genetics, sex differences and colour perception.

—Vaughan.

July 23, 2007

Spinning silhouette illusion:

I've just found this 'spinning silhouette' visual illusion which took ages to take effect but when it did it was so striking I thought at first it was faked.

The idea is that you keep looking and the woman suddenly 'flips' and seems to spin in the opposite direction. It's very impressive when it happens, but it seemed to happen so randomly that I wondered whether it had been programmed to randomly reverse.

However, I've found that if you cover image apart from the shadow of the feet and concentrate on seeing them rotate in the opposite direction, when you uncover the image, it too will seem to be in a reverse spin.

I'm guessing it works because our brain is making the best guess of a 3D shape from a 2D image. The silhouette from a real 3D rotating shape would look identical no matter what way it rotated.

Think about a rotating coin. No matter which way it turns, the silhouette would be the same - it would seem as if a disc was being progressively 'squashed' into a line and then back to a disc again.

As with all visual perception, our brain 'fills in the gaps' with best guesses, in this case to make it seem like a rotating 3D shape.

However, there's actually no information about which way its rotating, so it can suddenly 'flip' when our perception of the direction becomes unstable and another interpretation takes effect.

It's like a motion-based necker cube effect.

Link to Spinning Silhouette illusion.

—Vaughan.

July 18, 2007

An artistic impression of alcoholic delirium:

The picture is from this month's British Journal of Psychiatry and is entitled 'Memory image of acute alcoholic delirium'.

It was included in a 1919 book of cases studies of people with alcoholic delirium, otherwise known as delirium tremens or the DTs, and was drawn by a patient to communicate their hallucinatory experiences.

Delirium is a mental state where hallucinations and delusions are present, but unlike psychosis, there are also severe impairments in consciousness and cognitive function.

It typically resolves quickly, usually when the physical disturbance that caused it (e.g. fever, intoxication) subsides.

The author of the book, the Danish psychiatrist Einar Brünniche, explains the image:

'Finally, I should like to present an image, a reproduction of a coloured drawing, in which a patient, an artist, without words, but none the less very effectively and vividly, describes the memory of his past, alcoholic delirium... It shows us the many facets of hallucinations, their animal imagery, their life and mobility and their partial transformation of real objects; it shows us the air brimming with cobwebs, threads and smoke.

However, I should think that the image illustrates a stage at which the delirium has not yet reached its zenith since the patient is still bedridden. True, the hallucinations seem spooky, but they have not yet filled him with uncontrollable dread; he has not yet been stirred to action, he has not yet taken steps to ward off the danger. Besides, the picture speaks for itself'.

There's more at in this brief 'psychiatry in pictures' article at the link below.

Link to British Journal of Psychiatry full image and article.

—Vaughan.

July 05, 2007

Striking perspective shift illusion:

I've just stumbled across a remarkably simple yet fiendishly effective visual illusion that seems to give flat images the illusions of 3D depth. It works by quickly shifting between two images of the same scene taken from slightly different perspectives.

As we've noted when discussing other illusions, our brain generates the experience of seeing a 3D world by making the best it can out of the two fairly poor quality flat images that fall on the back of the retina.

Visual illusions usually have their effect by taking advantage of the brain's processes for inferring visual features.

These processes are really nothing more than educated guesses, and illusions essentially give the brain red herrings, misleading it to guess in the wrong direction, so we experience one visual feature in a context where it wouldn't normally appear.

In this case, the illusions give the misleading impression of depth in the context of an entirely flat image.

One clue the brain uses to infer depth is occlusion - things that are near the front of a visual scene will block those at the back. They just get in the way.

In fact, the lines in cartoons or diagrams are often just a representation of the occlusion contours - the edges of where one surface hide another.

However, although we can see that a cartoon drawing of a head is a 3D representation, we don't experience it as actually having depth. It doesn't seem to stand out from the page.

The perspective shift illusion flips between two images taken from slightly different perspectives and this seems to add a dynamic aspect - the illusion of movement.

Movement is often crucial for determing something's depth. Have you ever moved your head side-to-side when you see a puzzling sculpture to try and better understand its shape?

This allows us to see the relative depth of each of the occlusion contours by experiencing how much the foreground moves in relation to the background. Things nearer the front seem to 'move quicker' - something known as motion parallax.

I'm guessing by adding an impression of movement - some motion parallax - to a detailed photograph that already has other depth cues from the natural environment, the perspective shift illusion produces an impression of real depth.

If you want to know more about the cognitive science of 3D shape perception, there's a great review article by available Dr James Todd available online as a pdf file.

Otherwise, just spend a few minutes checking out the impressive visual effect.

Link to perspective shift visual illusion.

—Vaughan.

March 27, 2007

Single gene gives mice new sense of colour:

The journal Science reports a study showing that mice given a single gene can develop full colour vision. Mice, like most mammals except primates, are normally colourblind. The implanted gene, which is found in humans, is responsible for making a photopigment, a light-sensitive protein in the photoreceptors of the eye. The researchers from the Howard Hughes Medical Institute validated their findings with cell recording and with behavioural tests, demonstrating pretty conclusively that the mice really can see in colour, being able to make discriminations normal mice cannot, and this is because their photoreceptors are sensitive to long wavelength red light.

Because only a single new gene has this effect, the study is reported as demonstrating that primate colour vision could have evolved very suddenly. However, this angle is perhaps less suprising if we consider that colour vision is phylogenetically ancient - primate colour vision doesn't represent the first time it has evolved, rather primate colour vision is more of a recovery of the function which is found in many non-mammal species such as reptiles. The structural correspondence of this is that the appropriate apparatus for colour vision is extant in mammals - it is just that non-primate mammals lack the appropriate variety in their photopigments. The study is is another demonstration of the amazing ability of the brain to adapt to and take advantage of whatever sensory input is available to it (related to this, see this article on human tetrachromacy, via Slashdot)

—tom.

March 03, 2007

Movies and the McGurk Effect:

HacksZine is hosting a video by Brian Sawyer who riffs on the Mind Hacks book entry on the McGurk Effect and shows how this is used in movies.

The McGurk effect is, for example, where when you hear the sound of someone saying 'Ba' at the same time as you see them saying the sound 'Ga', you hear the second, because the information from your vision shapes how you perceive the sound.

Sawyer notes that this is commonly occurs in movies when they're dubbed, so despite the character saying 'You lousy melon farmer!' when this was obviously not what was said in the original, the dubbing doesn't seem completely out of whack.

Link to 'Hear with Your Eyes: The McGurk Effect' from HacksZine.

—Vaughan.

February 15, 2007

Faces, faces everywhere:

The New York Times has a brief article on why we have a tendency to see faces in chaotic or almost random visual scenes.

The tendency to see meaning in essentially random data is variously known as apophenia or pareidolia, and statistically would be known as a Type I error - a false positive.

Although it is controversial as to whether it is specifically dedicated to recognising faces, an area of the brain known as the fusiform gyrus is certainly heavily involved in perceiving faces.

The fact that this area is so specialised for faces might lead us to detect faces even when they are only suggested by a few dots, the position of clouds or the markings on just about anything.

"The information faces convey is so rich — not just regarding another person's identity, but also their mental state, health and other factors," he said. "It's extremely beneficial for the brain to become good at the task of face recognition and not to be very strict in its inclusion criteria. The cost of missing a face is higher than the cost of declaring a nonface to be a face."

There's a great web page with pictures of 'cloud faces' if you want to see how spectacular some of these effects can be.

Link to NYT article 'Faces, faces everywhere'.

—Vaughan.

February 12, 2007

Beauty and the average girl:

Flickr user Pierre Tourigny has created a series of composite images from popular portrait rating website Hot or Not? that nicely demonstrates our bias for perceiving average faces as beautiful.

He's made average images from a series of female faces but divided them up into the scoring categories, so there's an average of faces rated 5 to 5.4, 5.5 to 5.9 and so on.

The average image of the highest rated faces, and an average of faces from all rating categories are shown on the left, although the whole range is on Tourigny's Flickr page.

If you do have a look at the full series, you'll notice that the overall average face seems more attractive than the composite face created from images rated in the average range (5-5.4).

Previously on Mind Hacks, we reported on research that suggested that faces created from the average of many others possibly seem more beautiful because they're easier for the brain to process.

This may be because our brain does a similar averaging process to create a 'face template' which we use during face recognition.

Faces that deviate least from this template are easier to match and, therefore, tend to be seen as more attractive.

This, of course, is not the complete story as cultural ideas of what is considered beautiful and perhaps even specific ways in which a face could differ from the 'template' might also contribute to our subjective perception of beauty.

Link to Pierre Tourigny's 'Average Face Scale'.
Link to previous post on facial attractiveness perception on Mind Hacks.

—Vaughan.

January 23, 2007

The colourful world of naming and knowing:

The Economist has a short article on two recent studies which have examined the theory that our ability to perceive colours is influenced by the way a language labels different hues.

The general idea that language shapes our thoughts and experience is known as the Sapir-Whorf hypothesis.

For example, some languages don't have separate names for green and blue, and so this theory might predict that speakers of these languages would be less able to distinguish between the colours.

A less strong prediction might be that speakers of these languages might be able to distinguish between what we label as green and blue, but wouldn't necessarily make the division at the same point in the colour spectrum as English speakers typically do.

The Economist article discusses two recent experiments which have tested this idea, both in quite ingenious ways - suggesting that colour perception may indeed be influenced by colour naming.

Link to Economist article 'How grue is your valley?'.

—Vaughan.

October 31, 2006

Fading faces:

Wired Magazine has an article on a curious condition known as prosopagnosia where affected individuals cannot recognise people by their faces, despite being able to recognise and distinguish everyday objects with little trouble.

Until recently, it was thought that the condition only arose after brain injury - usually because of damage to an area of the brain known as the fusiform gyrus. This area is known to be heavily involved in face recognition.

It has more recently been reported as an inherited form, suggesting that some people are simply born with particularly bad face recognition skills.

The article looks at the work of neuropsychologist Dr Bradley Duchaine who is investigating the psychology and neuroscience of face recognition impairment, and discusses the experience of several people who have the condition.

One of the people is Bill Choisser, who created 'Face Blind!', one of the first and longest-running prosopagnosia websites on the net.

A particularly striking feature of his site is a self-published book which is an in-depth discussion of the condition and its effects.

Link to Wired article 'Face Blind'.
Link to Bradley Duchaine's page with copies of his scientific papers.
Link to Bill Choisser's website on prosopagnosia.

—Vaughan.

October 29, 2006

Mechanical brain sculptures:

Neurofuture is back with a bang after a late-summer sabbatical and has alerted me to some wonderful mechanical brain sculptures by artist Lewis Tardy.

Tardy has created a range of mechanical people and beasts all rendered as if they were powered by complex clockwork and hydraulics.

Some of these include cut-away heads, such as the one featured, with the thinking mechanisms exposed for the world to inspect.

Link to 'Mechanical brains' on Neurofuture.
Link to Lewis Tardy's website.

—Vaughan.

October 11, 2006

Average girls are hot:

Seed Magazine has an article on recent research published in Psychological Science that suggests that average faces are more attractive because they are easier for the brain to process.

The image on the right (go to the article for a bigger version) is a composite of a number of different female faces rated as attractive.

However, an average of all sorts of faces also tends to be attractive, as demonstrated by a page at the University of Regensburg (which also has an image of an hot average man as well).

In the Psychological Science article (pdf) the research team, led by Prof Piotr Winkielman, asked people to judge the attractiveness of shapes and dot patterns. Participants were more likely to judge the most average patterns as attractive.

In a further experiment, they used the same technique for faces and found the same result.

The researchers argue that the reason we prefer average faces is because the brain creates an idea of a 'prototype' face, based on the average of all the faces we have seen. Attractive faces are the ones that best match this prototype because they require less processing to match and recognise.

Link to Seed Magazine article.
Link to facial beauty research lab of Uni Regensburg (great examples).
pdf of research paper.

—Vaughan.

October 05, 2006

From sci-fi footnote to cutting-edge vision science:

There's a fascinating letter in today's Nature about how a footnote in one of Fred Hoyle's science fiction novels inspired a branch of research in vision science on how the brain estimates when moving objects will arrive at a certain point.

The characters in the book discover an ominous black cloud that appears to be heading towards Earth. Will the cloud hit Earth and, if so, when? The first question is solved when the characters examine the relative speed at which the cloud is translating across the night sky to the rate at which it is looming, or seeming to get larger. The second question is tackled with a bit of impromptu algebra in which the time until impact is calculated from the ratio of the current size of the cloud to its rate of change...

David Lee realized in the 1970s that the brain can use the ratio of size to its rate of change, previously identified by Hoyle, to estimate the imminence of arrival. David Regan realized soon afterwards that the brain can use the ratio of lateral speed to looming rate to calculate where an object is travelling....

Since the early work of Lee and Regan, a considerable amount of research in areas including psychophysics, motor action, neurophysiology and computational modelling has followed (see D. Regan and R. Gray Trends in Cognitive Sciences 4, 99–107; 2000). The whole body of work that exists today can be traced back to a casual footnote and a couple of sketches in a science-fiction novel.

Fred Hoyle was a professional astronomer working at Cambridge University so knew plenty about mathematics, but wrote a number of notable science fiction novels during his lifetime.

The full letter is freely available at the following link.

Link to Nature letter 'Hoyle's observations were right on the ball'

—Vaughan.

September 22, 2006

not your average PSY101 slide:

I'm putting together my lectures for the visual perception part of PSY101 (which I'm teaching in a few weeks). I was so proud of this particular slide that I had to share it:

Long-time readers of Mindhacks.com will know what I'm on about. Original paper available from the Homepage of Rodrigo Quian Quiroga

—tom.

July 11, 2006

after-effect illusions:

There's an illusion popular on youtube.com right now here. Have a look - it's a motion after-effect illusion. These are discussed in the book (Hack #25). The basic story is the same for all after-effects - continuous exposure to something causes a shift in sensitivity. For continuous motion this means that the visual system shifts its baseline so that, subsequently, stillness looks like movement in the opposite direction to the adapted-to direction. The nice thing about this demo is that is shows that you can have separate motion after-effects in different parts of your visual field. My top tip is to look at your hand at the end of the video for an extra-weirdness effect.

Also today someone asked me how the moving green dot illusion works. Answer: again, i think, it is an after-effect. The purple dots create a colour after-effect, a green dot. All the separate after-effects are joined together by the phi-phenomenon (Hack #27) to give an illusion of one single, moving, green dot.

To understand why we get after-effects, check out Hack #26 ('Get Adjusted'). Which makes this post the biggest plug for the book I've done in a long while!

—tom.

February 22, 2006

3D rooms:

Perception is a fundamentally underconstrained problem. You get information in through your senses, but not enough information to be absolutely sure of what is causing those sensations. A good example is perception of depth in vision. You get a pattern of light falling on your retinas (retinae?), in two dimensions, and from that you infer a three dimensional world, using various clever calculations of the visual system and some assumptions about what is likely. But because the process remains fundamentally underconstrained, there is always the possibility that you will see something that isn't really there - that is, your visual system will take in a pattern of information and decide that it is more likely to be produced by a scenario different from the real one.

Which is a all a long winded way of saying: "Look, cool! Illusions rooms!" (thanks Yalda)

They're painted so that from one particular angle the shapes line up and your visual system flips into thinking that it can see a flat, 2D, pattern when the reality is a disjoint 3D one. Awesome.

There's plenty more here

If you like this kind of stuff, also check out Christian's recent post on dangerous illusionary adverts

—tom.

February 16, 2006

Dangerous advertising:

Have you seen the new breed of lorry adverts? Surely they're dangerously offputting? ;-]

Thanks to J Mallory Wober for sending me the pic.
It reminded me of these.

—christian.

November 23, 2005

Misunderstanding mirrors:

If I asked you to draw a full-size outline of your head on a flip chart, and then to draw the outline of your head as it appears in the mirror, would you draw the two outlines the same size? You shouldn't do because the mirror image of your head (as it appears to you) is exactly half its true size, irrespective of how far you are from the mirror, a fact that few people realise. That's according to a new study published in Cognition by Marco Bertamini and Theodore Parks at the Universities of Liverpool and California.

They also found that most people believe the mirror image of their own head will grow smaller as they move away from the mirror - it doesn't it stays the same. Yet most participants correctly realised that if they watched the mirror image of another person's head, it would get smaller as that other person moved away from the mirror. Finally, only a minority of participants realised that the size of the mirror image of another person's head would get bigger as they, the participant, moved away from the mirror. Confused? Me too.

Link to study abstract

—christian.

September 20, 2005

Giant Squid - woah!:

The giant squid has the largest eye in the natural world. Although squid's eyes evolved on a separate branch of the tangle bank of life, they are remarkably like ours, except that they don't have the blind spot that human eyes have (Hack #16). This picture is from a book 'Extreme Nature' by Mark Carwardine (which the Guardian Weekend ran a piece on two weeks ago). This immature female is 17 foot long, but they go up to 49 foot apparently.

Photo from from here, some more on Giant Squid here

—tom.

August 25, 2005

Hack #103: See more with your eyes closed:

A reader writes (thanks nick!)

Not gonna impress any girls with this one, but... I was looking at my mother's ceiling fan the other day trying to determine how many blades it had. It was on its highest setting so it was nearly impossible to do. Until I blinked. If you blink rapidly, it disrupts the brains attempts at connecting frames of sight into continuous motion. Thus a whirling blur becomes a clear frame of sight, easily analyzed. Not sure where else this little trick could pay off. A nice illustration of the characteristics of our visual systems though.

Cool. Freed from the constraint having to make sense of continous input, your visual system can to make sense of the single 'frame' of input it does have. An example of less is more? I noticed something similar when riding my bike. When I glance down at the front wheel, it appears blurred. But when I look back at the road, my visual system delivers me a snapshot of the wheel, unblurred. What is happening - I'm guessing - is that as I move from looking at the wheel to the road ahead there is a moment of saccadic suppression [Hack #17] when visual input is cut off. Into this gap the 'frame' of the wheel is resolved. Also lending a hand may be a neural mechanism which turns off saccadic suppression if the velocity of the eyes matches that of a moving object (with your eyes stationary a moving object is blurred, with your eyes moving a stationary object is blurred, but if your eyes move at the same speed as an object you can get a clear image). For this to work the object needs to be nicely textured, so your low-level visual apparatus can gauge its velocity. Which explains why i get the effect on my mountain bike, which has big treads on the tyres, but not on a road bike, which has smooth tyres.

—tom.

August 24, 2005

changing diet might allow you to see infrared:

Thanks to Eric Lundquis for typing this up and putting it on the internet. It's an experiment done by the army and cited by Rubin, M. L., and Walls, G. L. (1969). Fundamentals of visual science. Springfield, Ill.: Thomas, p. 546, which is in turn cited Sekuler, R., and Blake, R. (1994). Perception (3rd ed.). Springfield, Ill.: Thomas, pp. 62-63:

The following story dramatizes how photopigments determine what one can see. During World War II, the United States Navy wanted its sailors to be able to see infrared signal lights that would be invisible to the enemy. Normally, it is impossible to see infrared radiation because, as pointed out earlier, the wavelengths are too long for human photopigments. In order for humans to see infrared, the spectral sensitivity of some human photopigment would have to be changed. Vision scientists knew that retinal, the derivative of vitamin A, was part of every photopigment molecule and that various forms of vitamin A existed. If the retina could be encouraged to use some alternative form of vitamin A in its manufacture of photopigments, the spectral sensitivity of those photopigments would be abnormal, perhaps extending into infrared radiation. Human volunteers were fed diets rich in an alternative form of vitamin A but deficient in the usual form. Over several months, the volunteers' vision changed, giving them greater sensitivity to light of longer wavelengths. Though the experiment seemed to be working, it was aborted. The development of the "snooperscope," an electronic device for seeing infrared radiation, made continuation of the experiment unnecessary (Rubin and Walls, 1969). Still, the experiment demonstrates that photopigments select what one can see; changing those photopigments would change one's vision.

—tom.

July 14, 2005

Another look at mindsight:

Last year, psychologist Ronald Rensink at the University of British Columbia proposed that some people have an alternative mode of visual experience – one that involves sensing but not ‘seeing’ – what Rensink dubbed ‘mindsight’. Now his claims have been forcefully rebutted by Daniel Simons and colleagues who argue it’s far more mundane than that: it’s all to do with how cautious people are in deciding whether or not they’ve seen something.

Rensink had performed a kind of change blindness experiment (see Hack #40) that involved participants reporting when they spotted a subtle change between two pictures. He invited participants to press one key when they ‘sensed’ a change between the pictures and to press another key only when they could ‘see’ the change and knew where and what it was. Rensink reported in Psychological Science that a subset of participants (30 %) showed evidence of what he dubbed ‘mindsight’: on a minority of trials they would report sensing the change at least a second earlier than they reported seeing it. “This mode of perception involves a conscious (or mental) experience without an accompanying visual experience”, Rensink explained. “The results presented here point towards a new mode of perceptual processing, one that is likely to provide new perspectives on the way that we experience our world”, he said.

But in this month’s issue of Psychological Science, Daniel Simons and colleagues at the University of Illinois dismiss Rensink’s findings. “Provocative claims merit rigorous scrutiny”, they said. “We rebut the existence of a mindsight mechanism by replicating Rensink’s core findings and arguing for a more mundane explanation…”.

Simons team argue that it’s all to do with how people interpret the instructions for ‘sensing’ and ‘seeing’ – that people who show Rensink’s mindsight are trigger-happy when it comes to saying they’ve sensed a change, but very cautious when it comes to saying they’ve seen exactly what that change is. By contrast, non-mindsighters interpret 'sense' and 'see' similarly, and are far more cautious about pressing the 'sense' button. In support of this, Simons' team found that so-called mindsight participants (those sometimes showing a significant lag between sensing and seeing) were far more likely than non-mindsighters to wrongly report sensing a change on 'catch-trials' when there wasn't actually a change between the pictures. What’s more, Simons' team said, Rensink’s criteria for what constitutes mindsight are arbitrary anyway (he chose a lag of 1 second between ‘sensing’ and ‘seeing’ but if, for example, he’d chosen 1.5 seconds, far fewer subjects would have been classified as showing mindsight). All in all, mindsight is starting to look more like a guess than a new mode of seeing!

—christian.

July 07, 2005

Time compression:

This could be a long shot, but if you're really enjoying yourself and you don't want time to go too fast, try keeping your eyes as still as possible. Concetta Morrone, John Ross and David Burr have just reported in Nature Neuroscience that subjective time is compressed around the onset of a saccadic eye movement. Saccades are the rapid, jerky eye movements that we perform thousands of times every day (see Hack #17) to align targets of interest with the high-acuity fovea at the centre of our eyes.

Morrone’s team asked participants to compare the time interval between two horizontal bars that were flashed up around the onset of a saccade, with the interval between a second pair of horizontal bars flashed up after the saccade. Participants said the intervals felt the same when the gap between the first two bars was 100ms and the gap between the second pair was 50ms – that is, subjective time was speeded up by a factor of two near the saccade onset.

This finding complements earlier research showing that space is also compressed around the onset of a saccade. These perceptual distortions are probably caused by remapping processes in the brain’s lateral intraparietal area that are meant to compensate for the visual disruption caused by making so many jerky eye movements all the time (again, see Hack #17).

So how does this research tie in with the ‘stopped clock illusion’ (Hack #18), in which subjective time is extended for stimuli perceived after a saccade? The phenomena may be related, but the researchers pointed to some key differences: the stopped clock effect also occurs for auditory and tactile stimuli, and is dependent on the size of the saccade. In contrast, the time compression reported here only occurred with visual stimuli, not with auditory clicks, and was largely independent of saccadic size.

—christian.

June 23, 2005

Optical street art of Julian Beever:

Julian Beever is a street artist who takes advantage of the way the brain understands the world to create some amazing artwork.

The brain works out our 3D experience of the world from the 2D light patterns that fall onto our retina at the back of the eye.

This process takes advantage of many of our implicit assumptions of the world, such as the fact that textures will fade as they go farther away, parallel lines will tend to converge in the distance and that objects will seem larger the closer they are.

Julian Beever's art uses a knowledge of these processes, so when seen from a certain angle, the pictures fool the visual system's inbuilt processes to produce a false sense of depth.

When seen from an alternative angle, the illusion breaks-down, and it's possible to see how the artwork was created.

There's plenty more examples of this amazing effect on Julian's pages that are well worth checking out.

Links to Julian Beever's homepage and street art page.
PDF of notes on 'An Introduction to Visual Perception'.

—Vaughan.

June 08, 2005

Out of the corner of my eye...:

When we direct our attention to an object, we usually look directly at it, but research just published in the journal Neuron looks at how we focus our attention on things that we notice 'out of the corner of our eye'.

A research team, led by David Melcher from Oxford Brookes University, has been investigating this process, known to psychologists as implicit selective attention.

They found when focusing on a certain attribute of visual experience - such as colour, the visual system automatically groups other objects of the same colour that move together, even if they are not directly involved in the task at hand.

They also found that objects are understood by the visual system in different ways, depending on whether the object was the focus of attention, or outside of it.

Objects being focused on were understood as wholes by using the fact that all the visual elements have the same surface, whereas objects outside the current focus were grouped in a more basic way, using the fact that visual elements are close together or move in a similar way.

Link to story from medicalnews.com
Link to summary of study from Neuron.
Link to lots of experiments, demonstrations and tutorials on attention.

—Vaughan.

April 07, 2005

Zoomquilt and the MAE:

So one of the things that didn't work so well at the Foyles talk was the demonstration of the Motion After Effect (or MAE to those of us who know and love it). Mick Porter has pointed out this animation zoomquilt which will definitely give you a good after-effect (thanks mick!). Zoom through the animation for a few cycles- you don't need to focus on anything in particular, just look at the center- and then stop it. When stopped everything should swirl back in the opposite direction for a bit: the motion aftereffect.

Why interesting? Well, it shows that motion has dedicated represention in the brain, aside from just being computed from just location and time (which is all you theoretically need to calculate). The after-effect - a percept of motion without anything changing location - shows that motion is specifically represented somewhere in the brain (in area MT in the visual cortex as it happens) and can be fooled.

Also, you can show that the effect is occuring in your brain, rather than in your eyes, by looking at the animation with one eye and then looking at it stopped with the other. You should get the effect transfering across.

—tom.

February 27, 2005

better to light a candle?:

She says: It's better to light a candle than to curse the darkness

He says: I wouldn't be so sure, maybe a candle would destroy your night-vision - without the candle your eyes could adjust to the lowered light levels (a process called adaptation, [Hack #26])

She says: But if you're in total darkness, there's no light at all to adjust to seeing

He says: Good point, so maybe it should be "It's better to wait for a bit, then, if your eyes don't adjust, you should light a candle rather than curse the darkness"

She says: How long do you have to wait until you know?

He says: Ah well, the cone receptors in the eye - which let you see colour - adapt fully after about 5 minutes. But it takes about 30 minutes for the rod receptors to fully adapt. These are the important ones for night vision, since they are specialised in detecting light or dark - which is presumably the fundamental information you are interested in.

She says: Okay. So it should be "It's better to sit in the dark for up to 30 minutes doing nothing, then light a candle rather than curse the darkness"?!

He says: Oh, you don't have to do nothing. Adaptation happens at the retina. You can prove this to yourself by adapting to the dark and then looking at a light with only one eye. One eye will adjust to the light, and the other (which you kept closed) will keep it's dark adaptation. Now if you go back to darkness you can switch between being blind (in your light adapted eye) and being able to see (in your other eye), just by openning and closing your eyes alternately. So, you can do anything you want with the rest of your brain, it shouldn't matter.

She says: So talking would be okay?

He says: Talking would be fine. Or whistling.

She says: So "It's better to wait in the dark to see if your eyes dark adapt (you can do anything you want while you're waiting) and only then, if they don't, light a candle rather than curse the darkness"

He says: You could even curse the darkness while you're waiting and get it out of the way. And really a red light would be better than a candle, because red spectrum light doesn't affect your dark adaptation (which is why cabin lights in aeroplanes and ships are red).

She says: "It's better to wait in the dark to see if your eyes dark adapt (you can do anything you want while you're waiting) and only then, if they don't, light a candle rather than curse the darkness. But it would be better if you had a red light rather than a candle for preference"

He says: That's it

She says: Snappy. I like it

He says: Someone should tell Amnesty

—tom.

February 13, 2005

Male faces with feminine features more attractive:

Recently released results from Dr Tony Little and his team, suggest that males with more feminine features are more widely attractive to women. Women who consider themselves highly attractive however, are more likely to go for classically masculine faces.

Dr Little is interested in identifying the features of attractiveness and explaining why we might have evolved to recognise and seek-out beauty.

The link might be explained by the fact that some physically attractive features are linked to levels of hormones (such as testosterone) that are present during development. These are also known to have an influence on fertility and coupling behaviour.

The researchers based their findings on data gathered from staff and students at the University of Liverpool, but have an online lab where you can take part in similar experiments.

Link to the research team's online lab.
Link to BBC News story on the research findings.

—Vaughan.

February 10, 2005

Psychopharmacology of emotion processing:

Some more stuff I learned about at the EPS meeting below the fold.

As before, caveats apply: this includes as-yet-upublished work, so things may not be quite as straightforward as put here; also, it's possible for me to miss, or even misunderstand, what the speaker is saying.

Catherine Harmer and her colleagues have been looking at the effects of serotonin on fear perception, as part of ongoing investigations into its role in this area. They make a persuasive case that these effects are genuine and are independent of the subjective level of anxiety the recipient feels. That is, the drug isn't just 'calming you down' and making you less jumpy: in addition, your cognitive system is oriented away from processing fear. The evidence that it influences cognition in the absence of anxiety changes comes from studies in which a single dose of a seretonergic agent is given; they found a cognitive effect of the dose even though subjective anxiety was unaltered, although interestingly the effect was that of a heightened response to fear stimuli.

In another experiment repeated sub-chronic doses were administered, and the effect reversed - fear was more poorly recognised - and was extended to other some other emotions, of which particular emphasis were given to Anger and Disgust. The most common kind of errors that were made were incorrect selections of happiness. In the talk, the findings were characterised as a decrease in negative processing; whilst I like the coherence this brings - antidepressants make you see the bad things in life more positively - I've been turning over an alternative hypothesis. What wasn't discussed in the talk, but was apparent from the figures, was the effects of chronic dosage on a couple of other emotions, surprise and sadness.

Surprise is as un-valenced(neutral) as an emotion can get, to the extent that many people are dubious about it being an emotion at all. Nevertheless, the drugs lead to worse accuracy on surprise expressions. Meanwhile, sadness is clearly a negative emotion - arguably the emotional state with the closest correspondence to depressive mood (though I stress they are not the same thing) - and recognition of sad faces is not affected by the drugs. This leaves the findings open to a different interpretation, I think, being that seretonergic drugs lead to a decrease in processing of urgent stimuli. Fear, disgust, surprise and anger all triggered by a cue that needs to be responded to, whilst happiness and sadness much more enduring states that are not initiated by an urgent situation. It seems plausible, and while I suspect the explanation presented is likely to be right, this objection would need to be countered first.

For those of you fans of what is happening inside the brain, an fMRI study showed less activation of the amygdala (implicated in the processing of a number of emotions, most notably fear) in subjects taking citalopram rather than placebo, when they were subliminally presented with fearful stimuli (meaning faces showing fear, rather than images of your parents discovering your stash).

In any case, the evidence that anti-depressants have a role in mediating our experience of emotional (or potentially stressing) elements in the environment casts an interesting perspective on what may be lifting the mood of the medicant.

Links: Earlier work showing the effects of a serotonergic agent on fear perception
Also, this looks spot on, but I can't source it in the journal, so it's probably been miscited in some way:

Harmer CJ, Bhagwagar Z, Cowen PJ, Goodwin GW. Acute administration of citalopram in healthy volunteers facilitates recognition of happiness and fear. J Psychopharmacol 2001a; 15 Suppl: A16.

—Alex.

January 26, 2005

Blind people can use the visual cortex to locate sounds:

A study just published in the open access journal PLoS Biology has reported that blind people might be able to use parts of the brain for locating sounds that sighted people normally use for vision.

Frédéric Gougoux and colleagues asked participants who had been blind from early life and who had previously demonstrated superior listening skills to try and judge the source of certain sounds while they were being brain scanned.

Unlike the normally-sighted participants, they showed activity in the occipital lobe, an area of the brain usually dedicated to processing visual information.

This suggests the brain of the blind participants had reorganised, or had organised differently, demonstrating how the brain can alter its structure depending on the demands placed on it.

This is a process known as neural plasticity and is known to be important in both early brain development and ongoing adult learning.

In fact, this isn't the first study to show that the brain of blind people might be organised differently. Research published in 1993 showed that braile reading abilities can be impaired by using magnetic stimulation to disrupt the activity of the occipital lobe.

The researchers suggested that this area had been recruited for touch and language skills, rather than vision.

Synopsis or full text from PLoS Biology.
Link to story on nature.com.

—Vaughan.

December 15, 2004

Hallucinations in macular degeneration:

The Fortean Times has an online article about the unusual experiences that can occur in a condition called macular degeneration, where light sensing cells in the part of the eye called the macular cease to work. As well as blindness in the central part of vision, hallucinations can occur.

"Hallucinations? What do you mean?" I asked, totally nonplussed. He outlined several forms of hallucination that were plaguing him. The first one to manifest was what Don described as looking like "a ball of string or basketwork, a globular shape with an aperture on one side". He would see this image as if projected onto walls or other surfaces. He could sometimes make out a small face inside the aperture, and on the occasions when this became particularly evident the basket-like effect would adjust around it like a bizarre headdress.

This hallucinatory state is known as Charles Bonnet syndrome, after the 18th century philosopher who noticed the condition in his father.

Link to full article on www.forteantimes.com

—Vaughan.

November 30, 2004

Dragon's Head:

Speaking of eyes following you around the room, this Dragon Optical Illusion is pretty cool. You make it out of paper and sellotape, and move around it with one eye closed. The head seems to move and follow you around. (There's a PDF to make the model, and a video to watch if you can't be bothered.) Here's the one I made:

The head's actually folded inwards, but we're so used to 3D objects bulging outwards that we see the model as if it's moving instead of its true shape. You don't even need to close one eye--from a few feet away it's pretty compelling. A neat instance of the visual system's assumptions dominating our current knowledge.

—Matt.

Hack 101: Make Eyes (or Anything) in Pictures Follow You Round The Room:

The eyes of some pictures seem to follow you around the room, like those of the famous WWI recruitment poster which helped garner almost 3 million volunteers in two years:

Try it. Get up and look at your screen from the side. Is he still looking at you? He should be.

Recently published research in the journal Perception [1] discusses how this effect works. The story was covered in the press (e.g. here). Turned around into a 'how to' rather than a simple 'explanation' it's perfect material for a hack. I saw it too late to include in the book so I'm putting it here.

So here we go: How can you design pictures of faces with eyes that will follow you round the room?

The answer is simple: photograph, or paint, the face looking straight out. If it's a photograph they must look straight at the lens of the camera. In the words of James Todd of Ohio State University, one of authors of the study, 'If a person in a painting is looking straight out, it will always appear that way, regardless of the angle at which it is viewed'

How does it work? First of all, this is only possible because pictures and paintings aren't 3D. They are semblances of 3D on a flat surface. This stops our brains calculating depth by comparing the images in the two eyes (how our brain calculates depth in images is covered in the book). Instead, our brains rely on other cues to depth, such as shading (the use of shadows to imply depth) and movement (all this is also covered in the book).

The explanation lies in how we interpret three-dimensional objects portrayed on a flat surface. Real three-dimensional objects look different depending on the angle because of the changing way light falls across them. But on the flat canvas, shading and light are fixed and the image looks the same from every angle. If the face is looking straight out from one angle, it will appear to be looking straight out at whatever angle it is viewed at.

In fact the only clue that the object in a picture isn't really looking straight out is that the near side of an object should get smaller if you look at it from one side. This doesn't happen in a natural way with a painting. Theoretically your visual system could use this information to figure out that pictures of objects aren't real and thus the eyes aren't really following you around the room, but it appears that they don't. The contradictory information is either overridden or disregarded.

If you want look at the original paper you see that the how-to-make-eyes-follow-you-around-the-room result is actually more of side-issue of the main thrust of the paper - which is a discussion of the visual mechanisms behind and correct interpretation of effect.

But the best thing, and the thing which I didn't see picked up by any of the press, is that you can do the trick with any object which has shading, and that for their investigation the authors used a statue showing a woman's bum.

Hilarious! Why did no one mention it in the press?

And it works, too, look:

They've made a picture of a bottom that follows you round the room. Ain't science great. (I'm absolutely convinced that more psychology should involve the analysis of naked bottoms.)

Refs:

1. Koenderink J.J., Doorn A.J. van, Kappers A.M.L., Todd J.T. (2004). Pointing out of the Picture. Perception, 33, 513-530. Here for subscribers

—tom.