The relationship between log-complex transforms of stimuli and the cortical responses they evoke

Two stimuli whose log-complex transform images in striate cortex are orthogonal square-wave gratings cause responses of equal magnitude in striate cortex but of unequal magnitude in extra-striate cortex. However, two other stimuli, orthogonal square-wave gratings in visual space, whose log transform images are identical except for phase shift, cause responses of equal magnitude in both striate and extra-striate cortex. A phase shift in the log-complex transform image represents a change either in the size or orientation of a form in visual space, parameters that do not affect its intrinsic shape. A change in the orientation of a contour line in the log-complex image represents either a change in the intrinsic shape of a form or its translation in visual space. Thus the results suggest that the extrastriate response may be related to the shape of an object in visual space.