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Abstract:
Attention involves enhanced processing of selected information by the brain. Its distribution across the visual field can change even when the eyes remain fixated. It can be redistributed across the visual field at will, and can also be shifted to a new location automatically because of a salient event. We exploited ‘change blindness' to map changes in the distribution of spatial attention brought about by a brief attention-grabbing cue. Change blindness occurs when a visual transient, such as a brief global blank, occurs between two images A and A′ that differ slightly from one another. Changes are only detected when attention is allocated to a location in both A and A′ (Rensink, 2000), because only then can the corresponding elements at that location be compared. We show that the probability of change detection at a location, and therefore the strength of visual attention at that location, depends on its spatial and temporal offset relative to a previously flashed spot that serves as an exogenous attentional cue. We have mapped the spatial distribution and timecourse of exogenously cued spatial attention with high resolution. Surprisingly, the ‘hotspot’ of attention elongates along the cue-fixation axis such that performance improves not only at the cued location but also at the location diametrically opposite the cued location, particularly when the exogenous cue is located on the vertical meridian. This may reflect inhibition of return emerging from properties of neuronal circuits in the superior colliculus that are involved in both exogenous attentional shifts and saccades.
