Proceedings of the 69th Annual Meeting of the Eastern Psychological Association, 69:89. 1998. [EPA 1998; Boston, MA.]

We show that shadows affect visual search in two different ways. (1) Search based on the angle of a shadow is slower when the shadow is rightside up (lighting from above) than when it is upside down (lighting from below). (2) The ratio of target-absent to target-present slopes increases to 3 or higher. These effects indicate that shadows are interpreted preattentively, and that they also influence strategic control of the search process.