Whether radial receptive field organization of the fourth extrastriate crescent (area V4A) gives special advantage for analysis of the optic flow. Comparison with the first crescent (area V2).

Recently, elongated comet-shaped receptive fields were discovered in the fourth extrastriate crescent (area V4A) of cats and monkeys. It was shown that the long axes of these receptive fields were oriented radially toward the centre of the retina. Such unusual "radial" organization of this extrastriate area led to the assumption that these neurons may contribute to the analysis of optic flow. To investigate this assumption we recorded activity of neurons in the V4A of cats during real motion in depth toward or away from a stationary visual scene. Responses of neurons in area V4A were compared with activity of neurons in area V2 under similar conditions of stimulation. Area V2 is known to be sensitive to motion but does not have radial organization. It was found that a substantial number of visual neurons in both areas did not fire at all when cats were exposed to motion in depth. Nevertheless, neurons with selective activation to direction of motion in depth were identified, but comparable numbers were found in both areas studied. We conclude that radial organization of the fourth extrastriate crescent does not provide any special advantage for the analysis of optic flow information.