Fall 1995 Volume 4, Number 4

Mapping Vision

Seeing, making mental use of things seen, and "seeing" them again in memory are fundamental to thought, and, thus, the brain's visual circuitry may have the potential to explain human phenomena ranging from creativity and imagination to disorders such as schizophrenia and memory loss.

John Reppas and colleagues at the Massachusetts General Hospital (MGH) are developing a road map of brain areas that receive and organize visual information. Humans are believed to have at least 30 such areas. The MGH team has described about 15, using functional magnetic resonance imaging (MRI) to scan the brains of human volunteers while they view visual stimuli and perform simple visual tasks.

Beyond simply mapping the areas, the group is interested in how the activity of each visual area contributes to perception. One approach to this question has been to study the volunteers' MRI response during visual illusions--that is, performing visual tasks that "trick the eye." During one illusion in which, after staring at a moving pattern, the subject perceives a stationary pattern to move, and another illusion in which the face of Lincoln appears to emerge from a mass of blocks, the investigators find that many "early" areas (sites in the brain to which signals from the optic nerve first travel) respond to the physical characteristics of the illusory image. But in at least two higher areas, brain activity seems to be tied to the "trick" or perception.

By repeatedly mapping the same subject's brain, the group may ultimately be able to chart the area-by-area flow of visual experience.

Maps of "early" visual areas. The visual world evokes systematic activity on the surface of the brain: Lines and shapes nearest each other in the visual world are also neighbors in neural representation. The rainbow colors (left) represent the different parts of the visual field; the subject stared at the central dot during the experiment. On right, color-coded similarly, three-dimensional, inflated and flattened versions of the brain of the same subject. (Courtesy of Mr. Reppas, from Sereno et al.: "Borders of Multiple Visual Areas in Humans Revealed by Functional Magnetic Resonance Imaging." Science, Vol. 268. Reprinted with permission.)

Table of Contents