Orientation bias of cat retinal ganglion cells.

Kuffler described the receptive fields of cat retinal ganglion cells as having a concentric arrangement. This has usually been taken to mean that they are approximately circular in form (see, for example, ref. 2). Hammond tested the circularity of the centre component of receptive fields by plotting a contour of isosensitivity to a small flashed spot. He concluded that centres were often ellipitical (average ratio of major to minor axis 1.23) and that more than 50% of the recorded cells had the major axis oriented within /+- 20 degrees of the horizontal. Such data are important for discussions of the neurophysiological basis of the 'oblique effect' (reduced visibility for periodic grating patterns when oriented away from the vertical or horizontal) observed in psychophysical experiments on humans because subcortical units are often assumed to be orientationally unbiased. Orientation selectivity is a prominent attribute of visual cortical neurones so analysis has usually emphasized the distribution of orientation selectivity at that level. The results presented here redirect attention to the retinal level since they reveal a previously unsuspected systematic relation between orientation bias of ganglion cells and their location relative to the area centralis.