Response to the velocity of moving visual stimuli of the brisk classes of ganglion cells in the cat retina.

Extracellular recording of the responses of cat retinal ganglion cells to narrow moving bars revealed systematic response variations with changes in stimulus velocity. These response variations were studied by collecting peri-stimulus histograms from brisk-sustained (X) and brisk-transient (Y) ganglion cells as narrow elongated bars were moved backwards and forwards across their receptive fields. Velocity-response curves were produced from plots of the amplitude of the main peak of the histograms as a function of velocity. The shape of these curves was found to be reasonably constant for both classes of ganglion cells. For a given cell, the peak of the velocity-response curve shifted to both a higher response level and a higher velocity as the stimulus contrast was increased. Within both classes of cells there was a systematic shift in the velocity-response curve as a function of the size of the receptive field centre. For brisk-sustained cells this was seen as an increase in both the response and velocity at the peak for larger centre sizes, while for brisk-transient cells it was an increase in velocity at the peak with negligible change in response. When the velocity required to produce a small criterion response was determined, there were distinct differences between the two classes of cells. When plotted on a double-logarithmic scale as a function of centre size the brisk-sustained cells had a slope of 2.00 while brisk-transient cells had a slope of 1.20. Within the area centralis brisk-transient cells responded more readily at high velocities than brisk-sustained cells. This was not the case in the peripheral retina, where both cell classes responded about equally at high velocities.