Movement sensitivity of retinal ganglion cells in monkey

The responses of on-center monkey retinal ganglion cells to small displacements of a spot light within the receptive field center were studied as a function of spot luminance. One group of cells reached peak rates of firing near 1000 spikes per sec with small displacements of spots with moderate and high contrast. These units had non-opponent color characteristics, relatively large receptive fields and phasic responses to a stationary flashing light. Easily distinguished from these cells were a group which had a maximum firing rate to displacement at moderate contrast. Above and below this optimum luminance, the firing rate decreased to zero. These cells had lower peak firing rates (100–200 spikes per sec), opponent color characteristics, tonic responses to stationary flashing light and relatively small receptive fields. All retinal ganglion cells isolated were potential candidates for detecting and transmitting movement information. For any individual units, histograms of responses to small displacements were very similar to histograms of responses to the stationary flashing spot. An ensemble code (cross-fiber analysis) is proposed to account for transmission of visual form and motion information to the central nervous system via tonic (x-type) and phasic (y-type) units.