The variety and complexity of visual perception in humans and other primates directly reflects the activity of a diverse system of separate cortical visual areas and their constituent functional subdivisions. The extent and significance of this latter subdivisional structure is only beginning to be appreciated. Nevertheless, it is increasingly apparent that to understand the functional organization of visual cortex as a whole, it will be essential to understand the functional organization of the constituent subdivisions and to understand their organization as multiple, concurrent processing streams. Recent evidence suggests that a key extrastriate visual area, V4, may contain a mosaic of subdivisions the receive their primary visual input from the cytochrome oxidase """"""""thin-stripe"""""""" and """"""""inter-stripe"""""""" subdivisions of area V2. Consequently, V4 subdivisions may form an essential component of two concurrent processing streams extending from primary visual cortex (V1) to visual areas of the temporal lobe. To provide direct evidence for these subdivisions and to describe their organization, two closely interrelated approaches will be employed. In the first of these, anatomical tracers will be used to reveal the selective connectivity of afferent terminals and efferent projection cells within V4. Particular emphasis will be placed on the relationships of these connections to the subdivisions of V2, to area MT and to the pulvinar. Both """"""""feedforward"""""""" and """"""""feedback"""""""" components will be examined, and the intrinsic connections of V4 will also be analyzed. The second approach will be to record and map the distribution of simple physiological properties within V4 and then to correlate those properties with the anatomical connectivity. Initially, the emphasis will be placed on responses likely to be associated with the segregated inputs from V2 subdivisions. Later, more complex responses associated with form processing will be studied in order to differentiate the subdivisions more fully and to lay the groundwork for future behavioral experiments. Together, these approaches will provide an integrated view of V4 subdivisions and will chart their relationships with other areas. this information should significantly extend our understanding of the visual processing streams which supply information to the temporal lobe for visual recognition and memory. These experiments are, therefore, an important step toward our ultimate goal of discovering the natural """"""""design"""""""" principles and specific mechanisms responsible for our visual abilities. In turn, this work may benefit the treatment of cerebral trauma and pathology, and may contribute to the design of a visual prosthesis for the blind.
