Featured Research

from universities, journals, and other organizations

Experiment Provides New Clues To The Location Of Visual Consciousness

Date:
August 30, 2001
Source:
Vanderbilt University
Summary:
A new test that measures what people see when viewing discordant images in the right and left eyes has produced important new clues about the location of some of the brain activity underlying visual consciousness.

A new test that measures what people see when viewing discordant images in the right and left eyes has produced important new clues about the location of some of the brain activity underlying visual consciousness.

Related Articles


The procedure, described in the Aug. 30 issue of the journal Nature, depends on a phenomenon called binocular rivalry first described in 1838 by Sir Charles Wheatstone. Using a device that he invented, Wheatstone discovered that when people are presented with dissimilar images in each eye, they report seeing first one image and then the other with the two images alternating unpredictably.

“Since this breakdown in binocular vision was discovered, it has been the subject of scientific interest because it involves the switching of visual consciousness without conscious control,” says Randolph Blake, professor of psychology at Vanderbilt. He, Hugh R. Wilson, a mathematician from York University in Toronto, and Vanderbilt graduate student Sang-Hun Lee devised the new test.

In normal binocular vision, sensory information from the two eyes is fused into a single, three-dimensional visual impression. Stereopsis, the ability to fuse two, two-dimensional images into a three-dimensional image, is the flip-side of binocular rivalry. Individuals with misaligned eyes can suffer from binocular rivalry. They generally cope with this condition in one of two ways. They either rely on the view from a single eye or they use each eye for a different purpose, such as close and far vision.

The question of which neurons are responsible for this effect is a matter of scientific controversy. Visual information from the eyes is routed to the back of the brain to an area called the primary visual cortex.

From there it is processed in an elaborate hierarchy that works its way forward in the brain through the temporal, parietal and frontal lobes. Some vision researchers argue that binocular rivalry must be handled at a low level in the brain’s visual processing hierarchy, while others maintain that it must be handled at higher levels. Results from the new test lend weight to the argument that the effect occurs at a low level in the visual cortex.

The procedure that Blake and his colleagues devised allowed them to measure the time that it takes for one monocular image to replace the other in the visual field. Using pairs of different patterns within the same-sized annulus, they determined that one pattern does not instantaneously replace the other.

Instead, the suppressed pattern breaks through at a specific location and then spreads in a wavelike fashion until it totally replaces the other pattern. The researchers found a way to trigger the alteration at a specific location on the ring and then measure the time that it takes the change-wave to reach a fixed point at the bottom of the annulus.

“The fact that the transition between the two images spreads gradually is an indication that binocular rivalry occurs at a lower level,” Blake says. “If it were handled at a higher level you would expect the change to be instantaneous.”

Another result that points toward the primary visual cortex is the trio’s observation that the rate at which the transition zone spreads increases with the size of the annular ring. This relationship is consistent with the way in which the eye and visual cortex are wired.

In the fovea, the portion of the retina at the center of the eye, the density of nerve connections is much higher than it is at the periphery. As a result, a signal traveling a given distance in the fovea stimulates more nerves than a signal traveling the same distance in the periphery. In the test, the person looks at the center of the ring. So, as the diameter of the ring increases, it stimulates nerves located further out on the periphery of the retina.

Therefore, if the alteration of images takes place in the visual cortex, a signal traveling halfway around a small ring must pass through a larger number of neurons than a signal traveling halfway around a large ring. The time it takes for a signal to propagate from neuron to neuron is roughly constant. So it makes sense that a signal which must pass through fewer neurons will travel faster than one which must pass through a larger number of neurons.

The final result implicating the primary visual cortex is the observation that when the suppressed pattern consists of concentric rings it spreads faster than when it is a radial pattern. Previous studies indicate that the primary visual cortex is specially wired to pick out continuous lines and curves. “This makes evolutionary sense because most of our visual environment consists of continuous features,” says Blake. So the observation that the alteration between the two images proceeds faster when the suppressed pattern is made up of continuous, concentric lines than it does with discontinuous, radial lines is also consistent with an origin in the primary visual cortex.

In the past decade, cognitive psychology has joined forces with neuroscience to address the question of the nature of conscious awareness. The new results are an important step in the process of discovering which neuronal processes go with consciousness, and which do not.

This research was funded by a grant from the Eye Institute at the National Institutes of Health.

For an overview of research on binocular rivalry, including examples of the test patterns used in the Nature article, go to Prof. Blake’s website: http://www.psy.vanderbilt.edu/faculty/blake/rivalry/waves.html


Story Source:

The above story is based on materials provided by Vanderbilt University. Note: Materials may be edited for content and length.


Cite This Page:

Vanderbilt University. "Experiment Provides New Clues To The Location Of Visual Consciousness." ScienceDaily. ScienceDaily, 30 August 2001. <www.sciencedaily.com/releases/2001/08/010830082707.htm>.
Vanderbilt University. (2001, August 30). Experiment Provides New Clues To The Location Of Visual Consciousness. ScienceDaily. Retrieved November 28, 2014 from www.sciencedaily.com/releases/2001/08/010830082707.htm
Vanderbilt University. "Experiment Provides New Clues To The Location Of Visual Consciousness." ScienceDaily. www.sciencedaily.com/releases/2001/08/010830082707.htm (accessed November 28, 2014).

Share This


More From ScienceDaily



More Health & Medicine News

Friday, November 28, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Ebola Leaves Orphans Alone in Sierra Leone

Ebola Leaves Orphans Alone in Sierra Leone

AFP (Nov. 27, 2014) — The Ebola epidemic sweeping Sierra Leone is having a profound effect on the country's children, many of whom have been left without any family members to support them. Duration: 01:02 Video provided by AFP
Powered by NewsLook.com
Experimental Ebola Vaccine Shows Promise In Human Trial

Experimental Ebola Vaccine Shows Promise In Human Trial

Newsy (Nov. 27, 2014) — A recent test of a prototype Ebola vaccine generated an immune response to the disease in subjects. Video provided by Newsy
Powered by NewsLook.com
Pet Dogs to Be Used in Anti-Ageing Trial

Pet Dogs to Be Used in Anti-Ageing Trial

Reuters - Innovations Video Online (Nov. 26, 2014) — Researchers in the United States are preparing to discover whether a drug commonly used in human organ transplants can extend the lifespan and health quality of pet dogs. Video provided by Reuters
Powered by NewsLook.com
Today's Prostheses Are More Capable Than Ever

Today's Prostheses Are More Capable Than Ever

Newsy (Nov. 26, 2014) — Advances in prosthetics are making replacement body parts stronger and more lifelike than they’ve ever been. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Health & Medicine

Mind & Brain

Living & Well

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins