The spatial distribution of attention during covert visual orienting.

Many studies of covert orienting of visual attention in response to informative pre-cues have focused on the spatial distribution of improved or impaired performance. One can find at least four different models in the literature, each describing a different distribution: the fixed gradient spotlight; the zoom lens spotlight; the hemifield activation hypothesis; and the flexible allocation of resources model. In previous work examining procedural details that might have led to the formulation of the hemifield activation hypothesis, it was postulated (Klein and McCormick 1989) that under conditions of uncertainty about which of two locations to attend, an observer may focus attention on a visual channel (i.e., midlocation placement of a fixed gradient spotlight) that is spatially intermediate. The present experiment was designed to distinguish among the four models of attentional distribution, and to test the midlocation placement strategy. Our findings show support for midlocation placement, demonstrate evidence against flexible allocation and hemifield activation, but could not differentiate between fixed gradient and zoom lens variants of the spotlight model.