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.

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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’.

Out of the corner of my eye…

corner_eye.jpgWhen 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.

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.

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

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.

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.

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 http://www.forteantimes.com

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.

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?

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