We show that cast shadows can have a significant influence on the speed of visual search. In particular, we find that search based on the shape of a region is affected when the region is darker than the background and corresponds to a shadow formed by lighting from above. Results support the proposal that an early-level system rapidly identifies regions as shadows and then discounts them, making their shapes more difficult to access. Several constraints used by this system are mapped (...) out, including constraints on the luminance and texture of the shadow region, and on the nature of the item casting the shadow. Among other things, this system is found to distinguish between line elements (items containing only edges) and surface elements (items containing visible surfaces), with only the latter deemed capable of casting a shadow. (shrink)

Cognitive impenetrability is really two assertions: (1) perception and cognition have access to different knowledge bases; and (2) perception does not use cognitive-style processes. The first leads to the unusual corollary that cognition is itself cognitively impenetrable. The second fails when it is seen to be the claim that reasoning is available only in conscious processing.