■ REVIEW : Parallel Processing, Asynchronous Perception, and a Distributed System of Consciousness in Vision

The primate visual brain is characterized by a set of parallel, multistage systems that are specialized to process different attributes of the visual scene. They occupy spatially distinct positions in the visual brain and do not project to a unique common area. These processing systems are also perceptual systems, because the result of activity in each leads to the perception of the relevant visual attribute. But the different processing-perceptual systems require different times to complete their tasks, thus leading to another char acteristic of the visual brain, a temporal hierarchy for perception. Together, these two characteristics—of parallel processing and temporal hierarchy—suggest that each processing-perceptual system can act with fair autonomy. Studies of the diseased human brain show that activity in separate processing-perceptual systems—especially those concerned with color and motion—can lead to the perception of the relevant attribute even when the other processing systems are inactive and ...