NONSPATIAL VISUAL-ATTENTION EXPLAINED BY SPATIAL ATTENTION PLUS LIMITED STORAGE

The use of nonspatial attentional mechanisms in search tasks was inves tigated by presenting observers with stimuli that contained 4-12 eleme nts located on a circle around the fixation point. The elements differ ed in one of six nonspatial 'dimensions', namely orientation, contrast , scale, number of cycles, 'shape', and place in the alphabet. The tar get element of the search task differed from trial to trial but was al ways presented to the observer as a nonspatial, visual cue. This cue w as displayed either before the stimulus (precue) or after the stimulus (postcue). Whereas a precue creates optimal conditions for the use of nonspatial attentional mechanisms, a postcue precludes benefits from their use. The fact that performance was better in the case of precued stimuli than in the case of postcued stimuli indicates that observers employed nonspatial attentional mechanisms. In the final analysis, ho wever, the effect of nonspatial attention reduces to spatial attention in combination with limited storage capacity.