Orientation bias of brisk-transient y-cells of the cat retina for drifting and alternating gratings.

Brisk-transient ganglion cells of the cat's retina were examined for orientation bias using two different stimuli: drifting gratings and alternating gratings, both of fixed contrast (50%) and fixed temporal frequency (2 Hz). Some cells were strongly biassed for both stimuli, some were not biassed for either while still others were strongly biassed for only one or other stimulus. The preferred orientations for the two types of grating tended to be the same, on average, but substantial differences were not uncommon. A systematic preference for radially-oriented gratings was evident when the stimulus was drifting but there was an additional preference for tangentially-oriented gratings when the stimulus was alternating. Orientation bias for drifting gratings often extended over a broad range of spatial frequencies and was maximum near the resolution limit. For alternating gratings, bias was evident only at the highest spatial frequencies. Results indicate that the arrangement of receptive field components responsible for linear and nonlinear kinds of behaviour may sometimes possess different axes of symmetry.