Visual Cortex: Seeing Motion

tion and speed brought the orientation of the `equivalent long bar' closer to or further from the orientation of the short bar. These results flatly contradict the bulk the literature on optical imaging, which postulates or reports explicit maps of preferred orientation, spatial frequency and direction [7--11]. According to this literature, a stimulus with a given orientation, spatial frequency and direction should have elicited responses in those pixels that lie at the intersection of the corresponding maps. The results come as less of a surprise, however, if one considers the literature on responses of single neurons. After a debate that raged in the 1970s, it was largely agreed that V1 neurons do not isolate this or that feature of the stimulus. For example, an elegant study by the De Valois group [12] demonstrated that V1 neurons do not encode orientation independently of other features: preferred orientation depends on stimulus spatial frequency as predicted by a simple model b