Neuronal responsiveness in area 21a of the cat.

Photic responsiveness was studied in cells of area 21a which was identified as a region containing few cells projecting to area 17, and was bounded to two other visual areas (posteromedial lateral suprasylvian area and area 19) providing abundant efferent projection to area 17. Area 21a cells were characterized by strong orientation, but demonstrated poor direction and end-stop selectivity, in contrast to strong direction or end-stop selectivity of cells in another two visual areas.