SPATIAL NONUNIFORMITIES IN VISUAL-SEARCH

Previous search experiments in this laboratory have been concerned wit h the marked differences in target detectability as a function of its location in the visual field-differences we have called a detectabilit y gradient-when subjects were required to detect a vertically oriented ''target'' among a number of distracter items having different orient ations. This gradient was characterized by a marked right visual field superiority as well as differences in the shape of the gradient in th e two half fields. A scanning model was proposed to account for these robust phenomena. The present experiments, using reaction time methods with vertical, horizontal, and colored targets have revealed marked d ifferences in both reaction time and detectability as a function of ta rget location and have isolated some of the spatial nonuniformities in the visual system which influence the shape of these gradients. The r esults reported here have forced us to abandon the scanning hypothesis in favor of a model in which attention is efficiently guided to the t arget. (C) 1996 Academic Press, Inc.