Abstract
Previous reports described differences in detectability of a target in a background of nontarget patterns as a function of its spatial location. These differences, referred to as a "detectability gradient, " have been attributed to target detection accomplished by a serial processing mechanism- a scan. The present experiments were designed to test the hypothesis that this scan is attentional in nature. The results provide additional evidence for the scanning hypothesis but do not support the view that this scan represents a series of attentional shifts.