Are shape differences detected in early vision?

Abstract

A series of visual search experiments explored whether early visual processes are sensitive to the overall shape of objects. Previous work (Wolfe & Bennett, 1997) has suggested that information concerning overall shape is not coded in early vision. However, in Experiment 1, we demonstrate that these previous findings are explicable in terms of non-target heterogeneity rather than an absence of shape information in early vision. In Experiments 2 and 3, we demonstrate that shape similarity, rather than individual contour similarity, can determine search efficiency. In Experiments 4 and 5, we show that manipulating the contrast polarity of contours and defining shape using texture significantly impeded search for an odd-one-out shape. The implications of these results for shape processing in early vision are discussed.