Nonspatial Visual Attention Explained by Spatial Attention Plus Limited Storage

Abstract

The use of nonspatial attentional mechanisms in search tasks was investigated by presenting observers with stimuli that contained 4-12 elements located on a circle around the fixation point. The elements differed in one of six nonspatial 'dimensions', namely orientation, contrast, scale, number of cycles, 'shape', and place in the alphabet. The target element of the search task differed from trial to trial but was always presented to the observer as a nonspatial, visual cue. This cue was 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, however, the effect of nonspatial attention reduces to spatial attention in combination with limited storage capacity.

Limitations for Change Detection in Multiple Gabor Targets

“…However in the pre-cued condition there was no set size effect: the discrimination threshold was identical for the one-target and four-target stimulus. This suggests that there is no degradation of performance due to a reduction in discriminability of multiple stimuli (deHaan, Lutz & Noest, 1996).…”