Chapter 19 Motion sensitivity and stimulus interactions in the striate-recipient zone of the cat's lateral posterior-pulvinar complex

Abstract

The cat's lateral posterior-pulvinar complex (LP-pulvinar) establishes reciprocal connections with the anterior ectosylvian visual (AEV) and lateral suprasylvian (LS) cortices; two regions which are believed to be involved in motion analysis. We have investigated the motion sensitivity of neurons in the LP-pulvinar complex by: (1) studying the responses properties of cells in the striate-recipient zone of the LP nucleus (LPI) to the drift of a two-dimensional texture pattern (visual noise); and (2) determining the extent to which the latter stimulus can modify the spatial frequency tuning function of LPI cells. Experiments were carried out on anesthetized normal adult cats. Almost all LPI cells (55 out of 63, 87%) responded to the motion of visual noise. For most units (39 out of 55, 71%), responses varied as a function of the direction of motion (bandwidth of 49 degrees). One-third of the LPI units did not exhibit any preference for drift direction of noise. For practically all LPI cells, responses to noise varied as a function of drift velocity. Optimal velocities were distributed from 2 to 35 degrees/s with a mean value of 27.5 degrees/s (means bandwidth of 2.5 octaves). The influence of visual noise on the spatial frequency tuning function of 22 LPI cells was also studied. For half of LPI cells, responses at all spatial frequencies were reduced when the grating and the texture pattern were moving in opposite directions (anti phase condition). This masking effect of noise was rarely observed when both stimuli were drifted in the same direction (in phase condition). These results suggest that the LP-pulvinar complex may be part of extrageniculate pathways involved in the analysis of motion of visual targets and/or the analysis of the relative movement between an object and its surrounding environment.