Neuroscience
Visual illusions are not only fun, they also help show how the brain works by exploiting its shortcomings. But what about using visual illusions for practical benefit? By making a step look taller than it really is, David Elliott and colleagues have demonstrated a way of doing just that.
Trips on steps are nasty for anyone, but for the elderly they can be fatal. Two thousand elderly people die in the UK every year following a fall, with the majority of these falls happening on stairs.
Elliott's team asked twenty-one students to judge the height of two steps, one of which was decorated with horizontal bars on its leading face, thus making it look shorter; the other was decorated with vertical bars, thus making it look taller (the right-hand step on the image above). Both steps were actually the same height. Asked to estimate the height of the steps, the students guessed the height of the vertically decorated step to be just over 5 mm higher than the other step.
Most importantly, an eight-camera motion capture system showed that when the students stepped onto the steps, they lifted their foot higher for the vertically decorated step compared with the horizontally decorated step by a distance of about 5 mm. This was true whether the students looked with both eyes, or just one.
Most people trip on stairs because their toes clip the edge of the step, so an illusion that leads people to exaggerate the clearance they give to a step, even by only a small amount, could have significant benefits in terms of reducing falls. Ideally the researchers ought to have included a 'control' step that didn't feature any decoration. However, this was a preliminary study and the researchers anticipate the illusion will be enhanced through future tests, increasing foot clearance still further.
As well as having practical implications, this study also has theoretical importance. An influential account of visual processing posits that there are two pathways in the brain: the dorsal "where" pathway and the ventral "what" pathway, with only the latter being prone to visual illusions. In support of this account, some experiments have shown that people's perception can be tricked by an illusion (such as the size of an object) while their motor system is unaffected, as demonstrated by the person using an appropriate grip size. The current observation that both perception and action were tricked by the design of the steps, challenges this dual pathway account.
"The most parsimonious explanation of our results is that visuomotor actions are directed by the visual system without the need to invoke two wholly separate pathways for action and perception in the dorsal and ventral streams respectively," the researchers said.
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David B. Elliott, Anna Vale, David Whitaker, John G. Buckley (2009). Does My Step Look Big In This? A Visual Illusion Leads To Safer Stepping Behaviour. PLoS ONE, 4 (2) DOI: 10.1371/journal.pone.0004577
Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.
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Alexander NB, Ashton-Miller JA, Giordani B, Guire K, & Schultz AB. Age differences in timed accurate stepping with increasing cognitive and visual demand: A walking trail making test. Jounal of Gerontology: A Biological Sciences and Med Sciences. 2005...
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Neuroscience
Visual illusion could help prevent falls
Visual illusions are not only fun, they also help show how the brain works by exploiting its shortcomings. But what about using visual illusions for practical benefit? By making a step look taller than it really is, David Elliott and colleagues have demonstrated a way of doing just that.Trips on steps are nasty for anyone, but for the elderly they can be fatal. Two thousand elderly people die in the UK every year following a fall, with the majority of these falls happening on stairs.
Elliott's team asked twenty-one students to judge the height of two steps, one of which was decorated with horizontal bars on its leading face, thus making it look shorter; the other was decorated with vertical bars, thus making it look taller (the right-hand step on the image above). Both steps were actually the same height. Asked to estimate the height of the steps, the students guessed the height of the vertically decorated step to be just over 5 mm higher than the other step.
Most importantly, an eight-camera motion capture system showed that when the students stepped onto the steps, they lifted their foot higher for the vertically decorated step compared with the horizontally decorated step by a distance of about 5 mm. This was true whether the students looked with both eyes, or just one.
Most people trip on stairs because their toes clip the edge of the step, so an illusion that leads people to exaggerate the clearance they give to a step, even by only a small amount, could have significant benefits in terms of reducing falls. Ideally the researchers ought to have included a 'control' step that didn't feature any decoration. However, this was a preliminary study and the researchers anticipate the illusion will be enhanced through future tests, increasing foot clearance still further.
As well as having practical implications, this study also has theoretical importance. An influential account of visual processing posits that there are two pathways in the brain: the dorsal "where" pathway and the ventral "what" pathway, with only the latter being prone to visual illusions. In support of this account, some experiments have shown that people's perception can be tricked by an illusion (such as the size of an object) while their motor system is unaffected, as demonstrated by the person using an appropriate grip size. The current observation that both perception and action were tricked by the design of the steps, challenges this dual pathway account.
"The most parsimonious explanation of our results is that visuomotor actions are directed by the visual system without the need to invoke two wholly separate pathways for action and perception in the dorsal and ventral streams respectively," the researchers said.
_________________________________
David B. Elliott, Anna Vale, David Whitaker, John G. Buckley (2009). Does My Step Look Big In This? A Visual Illusion Leads To Safer Stepping Behaviour. PLoS ONE, 4 (2) DOI: 10.1371/journal.pone.0004577Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.
- Magic Trick Fools Us But Not Our Eyes
The magician throws the ball twice into the air and catches it, then he throws it a third time and it vanishes! Of course, he’s really secreted the ball in the palm of his hand, so why do so many observers believe they’ve seen the ball vanish mid-flight?...
- The Foot Is Also Quicker Than The Eye
Scientists at the Institute of Neurology have shown that reaching movements with the foot can be controlled by the same kind of rapid, sub-conscious processing as the hand. Participants were asked to lift and place one of their feet as quickly as possible...
- Abstract Of The Day: Cognitive Demands On Functional Decisions
Alexander NB, Ashton-Miller JA, Giordani B, Guire K, & Schultz AB. Age differences in timed accurate stepping with increasing cognitive and visual demand: A walking trail making test. Jounal of Gerontology: A Biological Sciences and Med Sciences. 2005...
- Visual Illusions And Direct Perception
A while back I reviewed a bunch of papers by Rob Withagen who is currently arguing that while perception is not typically based in specifying variables, it can and should still be ecological in nature. While we are also developing an account of information...
- A Note On Holt On Visual Illusions (heft, 2001)
This is a visual illusion. When you look at it, there appears to be a great deal of motion as things rotate in various directions. But there's no actual motion; this isn't an animated display and you can verify this by fixating the centre or touching...