ATTENTIONAL INTERFERENCE AT SMALL SPATIAL SEPARATIONS

The spatial characteristics of attention were studied by measuring the accuracy with which two target letters could be identified from a cir cular display of 24 characters. Traditional notions of spatially-limit ed regions of attentional enhancement predict that performance should be best when the pair of targets fall within the boundaries of a singl e attentional 'window'. The results were opposite to this expectation: performance was poorest when the targets were close together and impr oved with increasing target separation. The effects were not due to la teral sensory masking or to sensory transients and were replicated wit h several different types of attentional cues. Two possible models are proposed to account for the observed effects of target separation. Th e first model assumes that attending to one location necessarily reduc es processing in the local surround. The second model proposes that th e poorer performance observed at small target separations results from imprecise targeting when attention is directed to a pair of nearby lo cations. Both models illustrate spatially-local limits on processing c apacity that attention is unable to circumvent. Enhancement at one loc ation is achieved primarily at the expense of the immediate surround. Such spatially-local tradeoffs in processing capacity could have the u seful consequence of making the attended target stand out even more ag ainst the immediate background. (C) 1998 Elsevier Science Ltd. All rig hts reserved.