NEURONAL RESPONSIVENESS TO 3-DIMENSIONAL MOTION IN CAT POSTEROMEDIAL LATERAL SUPRASYLVIAN CORTEX

The neuronal responsiveness to three-dimensional (3D) motion in cat po steromedial lateral suprasylvian (PMLS) cortex was studied using a com puter-controlled, stereoscopic 3D graphic display capable of reproduci ng the major visual cues for natural 3D motion, including motion dispa rity, size, texture, and shading changes. The animals were anesthetize d with nitrous oxide supplemented with alphaxalone, and paralysis prev ented eye movement. Systematic investigation of neuronal responsivenes s to 3D motions in 26 different directions revealed that more than hal f of the PMLS cells were selectively responsive to approaching (AP cel ls, 112 of 271) or recessive motion (RC cells, 64 of 271). The remaini ng cells were selectively responsive to frontoparallel motion (FP cell s, 49 of 271) or nonselectively responsive to motion in multiple direc tions (NS cells, 46 of 271). The dependency on these visual cues was i nvestigated as a reduction in the response amplitude or the response s electivity for the removal of a single cue from the motion stimuli con taining the full visual cues. The AP and RC cells showed a strong depe ndency on the motion disparity cue, moderate dependency on the size cu e, and weak dependency on the texture and shading cues. The FP cells s howed no dependency on those visual cues. The cue dependency analysis indicated the existence of nonlinear interactions between those visual cues. Comparison of the responses to a combination of the motion disp arity and size cues with the summed responses to each of the individua l cues revealed that the responses to the combined cues are roughly pr edicted as a linear sum between the preferred responses. This comparis on also showed nonlinear summation between the nonpreferred responses, i.e., responses to the combined cues were smaller than the summed res ponses. A similar quasilinear summation of the preferred responses bet ween the two eyes and a nonlinear summation of the nonpreferred respon ses were found in the AP and RC cells for the motion disparity stimulu s. All of these observations indicate that quasilinear and nonlinear i nteractions of the responses to various stimulus elements underlie the 3D motion responsiveness of the PMLS cells.