Macaque ganglion cells, light adaptation, and the Westheimer paradigm

Retinal adaptation mechanisms are considered relative to the Westheimer paradigm. Responses to a probe presented upon pedestals were obtained from macaque ganglion cells. On-center magnocellular (MC) cell responses decreased to a plateau as pedestal diameter increased, consistent with operation of a local adaptation pool. Off-center cells also demonstrated a vigorous response with small pedestals, but as pedestal size increased, responsivity decreased and then partially recovered as pedestals encroached upon the surround. The response trough was due to a profound suppression of maintained activity. Comparison with psychophysical data suggests a multiple physiological substrate for the Westheimer paradigm, involving an interaction between adaptation pools, changes in maintained firing due to center-surround mechanisms and a cortical component.