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11/15/2005

Sensing without seeing

Patients claiming they can see despite being blind from brain damage offer indirect evidence of the existence of "blindsight," a phenomenon in which people with damage to the primary visual cortex report not seeing something, but correctly identify an object's shape and location when asked to guess. A new study by Rice psychologists offers further proof that even when that region of the brain shuts down, we are still unconsciously processing detailed visual information such as color.

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People who have lost their sight as a result of brain damage may one day be able to "see" again. Rice researchers not only have definitively identified the region of the brain most responsible for our ability to see, but they have provided new evidence that when the normal route for processing visual information is disrupted, other pathways in the brain may still be processing that information, albeit unconsciously.

Photo by Jeff Fitlow

Tony Ro, associate professor of psychology, administers a brief, noninvasive magnetic pulse to a volunteer’s visual cortex, the area at the back of the brain that processes what the eyes see, to induce temporary, reversible blindness for a research study.

"Our study not only supports the theory that people do process visual information unconsciously," says Rice psychologist Tony Ro, "but we believe different pathways of the brain may be involved depending on the type of visual information being processed."

Ro believes their findings might provide insight into more effective treatment and rehabilitation for people who have had vision loss as a result of brain damage in the primary visual cortex.

"Because we know other pathways can still process information in the absence of a functioning primary visual cortex, perhaps by exercising them, people might recover some of their visual processing capacities," Ro says.

In a study titled "Unconscious Processing of Orientation and Color Without Primary Visual Cortex," published in the Proceedings of the National Academy of Science, Ro, Rice graduate student Jennifer Boyer and Stephanie Harrison, a summer intern, set out to confirm whether people can process information unconsciously and what brain areas might be involved in processing visual information if the normal processing pathways were damaged.

Using a harmless, noninvasive technique called transcranial magnetic stimulation or TMS, the researchers simulated damage to the primary visual cortex   --- the area of the brain associated with sight - by inducing temporary, reversible blindness in their subjects.

Participants were asked to identify horizontal or vertical lines flashed on a computer screen within the fractions of a second they were temporarily blinded.   In a second experiment, they were asked to identify a red or green dot on the computer screen under similar circumstances. In both trials the subjects who underwent TMS reported they were unable to see either the lines or the dots.   When asked to guess the orientation or color of the dots, the accuracy of their responses was startling. Although the participants didn't actually see the lines, they were 75 percent accurate in their guess as to whether the lines on the screen were horizontal or vertical. Their accuracy in guessing the color of the dots was 81 percent and in some cases nearly perfect.

"We knew which parts of the brain processed the visual features of orientation and color, so our study helped to definitively identify those areas of the brain which still function in processing visual information," Ro says.

The researchers also collected confidence ratings in which the subjects rated how confident they were regarding the correctness of their guess.   Although most participants expressed little confidence in their accuracy, the more confident they were, the greater their accuracy.

In the future, Ro plans to look at how complex unconsciously processed information can be - for example, whether we can unconsciously process multiple features such as the color and shape of an object.

"We're also studying whether unconscious representations can influence our interactions with our environment and affect our decision-making," Ro says.

Before joining the psychology department at Rice in 1999, Ro was a postdoctoral fellow at University College London where he began work on face perception and attention as part of a Human Frontiers Science Program project, which supports novel, innovative and interdisciplinary basic research on topics ranging from molecular and cellular approaches to systems and cognitive neuroscience.

A graduate of the University of California where he earned his Ph.D. degree in neuroscience, Ro completed his undergraduate training at the University of California, Berkeley. His research has been published in a number of scholarly journals, including the Journal of Experimental Psychology, the Journal of Cognitive Neuroscience, Psychological Science, Experimental Brain Research and in the Proceedings of the National Academy of Sciences.

For more information on this research, contact Ro at tro@rice.edu or B.J. Almond in the office of News and Media Relations at balmond@rice.edu .

A PowerPoint file is available for download at http://www.rice.edu/media/pnascov.ppt.