Discriminability of stimuli varying in physical and retinal orientation.

In 2 discrimination reaction-time experiments, adult human Ss responded faster to horizontal and vertical stimuli (lines or rectangles) than to stimuli tilted 45 ° right and left. When S viewed the stimuli with his head tilted 45°, so that physical and retinal orientation were in opposition, it was on the physical rather than the retinal horizontals and verticals that performance was superior. In another experiment head position was changed 45 ° after a period of learning. Ss required to give the same responses to the same physical orientations did much better on the transfer task than those required to give the same responses to the same retinal orientations. The latter were not significantly superior to a pure transposition group for whom the S-R relationships were shifted both physically and retinally. The octopus discriminates easily be- explanation of these behavioral results tween a horizontal and a vertical rec- is in terms of receptive field configuratangle, but not between two oblique tions, particularly since Young (1962) rectangles that also differ by 90 ° has observed that dendritic trees in the (Sutherland, 1957, 1958, 1960). Very visual system of the octopus show prosimilar results are obtained with pre- liferation most often in vertical and school children (Rudel & Teuber, horizontal directions, and since Hubel 1963); also with goldfish (Mackintosh and Wiesel (1959) have found that & Sutherland, 1963). In the cat, how- slope analyzers in the cat's visual corever (Sutherland, 1963), no such dif- tex are about evenly distributed over ference is found, and Sutherland re- all orientations. One is tempted to marks in passing that the oblique suppose, from the behavioral evidence, stimuli seemed less confusable to the that man's primary visual system concats than to him. The most obvious tains a preponderance of vertical and