 |
 |
 |
|
|
|||||||||
|
|
|
|||||||||
|
|
|
|||||||||
|
|
|
|||||||||
|
|
|
|||||||||
Studies of the brain
Beginning around 1970, researchers began to seriously study the visual brain. Among the chief discoveries is that it is composed of many different visual areas that surround VI. Each group of areas is specialized to process a particular attribute of the visual environment by virtue of the specialized signals that each receives from VII. Cells specialized for a given attribute such as motion or color are grouped together in anatomically identifiable compartments within VI, different compartments connecting with different visual areas outside VIII, thus conferring their specializations on the relevant areas. VI, in brief, acts much like a post office, distributing different signals to different destinations; it is but the first, though essential, stage in an elaborate machinery designed to extract the essential information from the visual world. What we now call the visual brain is therefore VI plus the specialized visual areas with which it connects, directly and indirectly. We therefore speak of parallel systems devoted to processing simultaneously different attributes of the visual world, a system comprising the specialized cells in VI plus the specialized areas to which these cells project. Vision, in brief is modular. The reasons for evolving a strategy to process in parallel the different attributes of the visual world have been debated but it seems plausible to suppose that they are rooted in the need to discount different kinds of information when acquiring knowledge about different attributes. With color, it is the precise wavelength composition of the light reflected from a surface that has to be discounted whereas with size it is the precise viewing distance and with form the viewing angle.
Recent evidence has shown that the processing systems are also perceptual systems in that activity in each can result in a percept without reference to the other systems; each processing-perceptual system terminates its perceptual task and reaches its perceptual end-point at a slightly different time from the others, thus leading to a perceptual asynchrony in vision color is seen before form which is seen before motion.. the advantage of color over motion being of the order of 60-100 ms. Thus visual perception is also modular. In summary, the visual brain is characterized by a set of parallel processing perceptual systems and a temporal hierarchy in visual perception.