Responses of visual cortical neurons to curved stimuli and chevrons.

Single cells were recorded in area 17 of anaesthetized and paralyzed cats and their responses to curved stimuli and chevrons compared. Striate cells exhibited three different response patterns. A first group responded optimally to a straight line (i.e. zero curvature) and responded similarly to chevrons and to curved lines. A second group responded to all curvatures and was broadly tuned for the straight line when tested with chevrons. A third group responded only to large curvatures, many (2/3) to both signs of curvature and a number (1/3) to only one sign. Cells in this group responded differently to chevrons and curved lines. Cells in these three classes differed both in length-response curve and in width of orientation tuning. Laminar analysis revealed that the three classes are distributed differently across cortical layers. These data shed new light on the finding of Malpeli and coworkers that orientation is extracted at least twice in a cortical column.