Cascade processes in picture identification (1988)

The neuropsychological phenomenon of extinction occurs when two stimuli are simultaneously presented, and the patient, who has no difficulty seeing each stimulus, presented alone, reports seeing only one of them. Although classically associated with parietal damage, extinction can result from a variety of brain lesions. This deficit in perceptual report when multiple stimuli compete for selection can be attributed to a chronic limitation in visual attention resulting from the brain lesion. The constraint on visual selection in patients with extinction can be overcome by grouping stimuli into single objects. Several grouping factors have been shown to be important, including collinearity, connectedness, common shape, common contrast polarity, common region and whether elements are parts of a known shape. In one study, a patient could select two words if they formed a verbal association, but when unrelated word pairs were presented, selection was limited to one word. Thus we conclude that implicit coding of the action relationship modulates visual selection.