New research advances understanding of size perception

March 12, 2012
Apparatus used in the fMRI experiment. A) Induction of an afterimage by means of a bright light attached on the back of a foldable screen; B) The subject projected the afterimage upon a surface placed at different distances from the subject's eyes.

Neuroscientists from Western University have taken the all-important first step towards understanding the neural basis of size constancy or the ability to see an object as having the same size despite the fact that its image on the retina changes constantly with viewing distance.

The findings were revealed this week by in a study titled, "Retinotopic activity in V1 reflects the perceived and not the retinal size of an afterimage."

"If we look at a car driving away from us, its image on our retina gets smaller and smaller -- yet we don't see the car as shrinking in size but rather as staying the same size. This is size constancy," explains Melvyn A. Goodale, Canada Research Chair in Visual Neuroscience and Director of Western's and Mind Institute.

The test that Goodale and his colleagues Irene Sperandio and Philippe Chouinard employed was asking subjects to stare at a light long enough to create an 'afterimage' on the retina.

The video will load shortly

As the test subject ‘projected' an afterimage onto surfaces at different viewing distances, his or her brain was scanned in Western's 3T fMRI (functional magnetic resonance imaging) scanner. As expected, people reported that the further the surface on which they saw the afterimage, the larger the afterimage appeared to be. Remarkably, the brain scans revealed that this difference in the perceived size of the afterimage was playing out very early in the visual pathway – in a brain area that that is typically thought to reflect only what is happening on the retina.

Frame_0. Primary visual cortex at rest (there is no activation).

Frame_1. Activity in primary visual cortex in response to the light.
Frame_2. Activity in primary visual cortex in response to the afterimage.
Take the test: 'Project' your own afterimage

"We found that activation in the primary visual cortex (V1), which is an area located in the back of the brain that receives inputs from the eyes, was affected by the apparent size of the afterimage even though the information coming from the retina was always the same," says Goodale. "This suggests that V1 is a possible neural substrate for size-distance scaling."

Goodale says if the human brain didn’t invoke size constancy; the world would appear to be a very strange place indeed, with objects expanding as we moved closer to them and shrinking as we moved away. 

The video will load shortly

"To maintain a stable visual world, we need to know how far away objects are from us so that our brain can make the appropriate adjustments to the size of the image coming from the retina," says Goodale. "Findings from this research are relevant not only for understanding how our brain represents the size of an object but also to understand medical conditions, such as Alice in Wonderland Syndrome, where patients experience visual distortions in which the world gets oddly smaller or bigger."

Goodale suggests that the principles illuminated by this work can also be usefully applied to computer-based recognition devices and artificial visual systems that use brain implants.

Explore further: What the brain sees after the eye stops looking

Related Stories

What the brain sees after the eye stops looking

November 8, 2011
(Medical Xpress) -- When we gaze at a shape and then the shape disappears, a strange thing happens: We see an afterimage in the complementary color. Now a Japanese study has observed for the first time an equally strange ...

'I can hear a building over there': Researchers study blind people's ability to echolocate

May 25, 2011
It is common knowledge that bats and dolphins echolocate, emitting bursts of sounds and then listening to the echoes that bounce back to detect objects. What is less well-known is that people can echolocate too. In fact, ...

Scientists trick the brain into Barbie-doll size

May 25, 2011
(Medical Xpress) -- Imagine shrinking to the size of a doll in your sleep. When you wake up, will you perceive yourself as tiny or the world as being populated by giants? Researchers at Karolinska Institutet in Sweden may ...

Recommended for you

Scientists capture first image of major brain receptor in action

July 24, 2017
Columbia University Medical Center (CUMC) researchers have captured the first three-dimensional snapshots of the AMPA-subtype glutamate receptor in action. The receptor, which regulates most electrical signaling in the brain, ...

Research identifies new brain death pathway in Alzheimer's disease

July 24, 2017
Alzheimer's disease tragically ravages the brains, memories and ultimately, personalities of its victims. Now affecting 5 million Americans, Alzheimer's disease is the sixth leading cause of death in the U.S., and a cure ...

Illuminating neural pathways in the living brain

July 24, 2017
Using light alone, scientists from the Max Planck Institute of Neurobiology in Martinsried are now able to reveal pairs or chains of functionally connected neurons under the microscope. The new optogenetic method, named Optobow, ...

Study suggests link between autism, pain sensitivity

July 24, 2017
New research by a UT Dallas neuroscientist has established a link between autism spectrum disorder (ASD) and pain sensitivity. 

Eye test could help diagnose autism

July 24, 2017
A new study out in European Journal of Neuroscience could herald a new tool that helps physicians identify a sub-group of people with Autism spectrum disorders (ASD). The test, which consists of measuring rapid eye movements, ...

The neural codes for body movements

July 21, 2017
A small patch of neurons in the brain can encode the movements of many body parts, according to researchers in the laboratory of Caltech's Richard Andersen, James G. Boswell Professor of Neuroscience, Tianqiao and Chrissy ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.