DISTINGUISHING DIRECTION SELECTIVITY FROM ORIENTATION SELECTIVITY IN THE RABBIT RETINA

Direction selectivity and orientation selectivity were examined in the direction-selective (DS) and orientation-selective (OS) ganglion cell s in the rabbit retina. Spike activities were recorded ill vivo using tungsten-in-glass electrodes. Three types of visual stimuli (flashing slit, moving edges behind a slit, and whole-field drifting gratings) w ere used to distinguish these attributes. Fourier analysis was perform ed on data obtained using drifting gratings as proposed by Worgotter a nd Eysel (1987). Results from both angular and Fourier (polar angle fr equency) domains were consistent. DS cells had strong directional comp onents and varying strength of orientational components; they also had intact inhibitory surrounds. The phase of the biased orientation did not have a consistent relationship with the preferred direction. OS ce lls had predominant orientational components and very weak directional components. We conclude that the orientation bias does not contribute to the generation of direction selectivity, and that the mechanism of this bias of DS cells is rather different from the mechanism that gen erates orientation selectivity in rabbit OS cells. There are indicatio ns that it is similar to the mechanism shown to cause orientation bias in cat concentric cells.