Neural correlates of motion after-effects in cat striate cortical neurones: interocular transfer.

Interocular transfer of motion after-effects was assessed in the lightly-anaesthetized feline striate cortex. Neurones were adapted with square-wave gratings of optimal orientation and spatial frequency, or with randomly textured fields, drifting continuously at optimal velocity in their preferred or null directions. Neural after-effects were assessed as consequent changes in directional bias, using similar test patterns swept back-and-forth in the same directions and presented to the same or opposite eyes. All results were compared with controls, embodying similar tests following a period of exposure to a uniform background or stationary textured field. The majority of binocularly-driven complex and simple cells tested evinced positive interocular transfer of after-effects. After-effects, whether elicited monocularly or interocularly, were direction-specific. With gratings, after-effects elicited interocularly were always weaker than those obtained monocularly. After-effects evoked monocularly by texture adaptation were weak in comparison to those evoked by gratings; interocular transfer in this case was negligible. In neurones strongly dominated by one eye, adaptation of the non-driving eye yielded, at best, extremely weak after-effects through the other eye. In purely monocular neurones, no transfer could be induced. These results confirm the expectation that motion after-effects arise cortically rather than precortically. The partial interocular transfer seen in binocularly-driven cortical cells suggests that these neurones represent a second-stage processing of inputs from lower-order complex (or simple) cells, themselves driven monocularly or strongly dominated by one eye.