Evaluating Spatial-Based Attention Exclusivity for Hemifield Independence: Accounting for Effects of Salience, Distractor Preview, and Spatial Certainty

摘要

Previous research by Alvarez and colleagues (2012) found evidence of hemifield independence for spatial, but not feature-based attention in visual search. However, reaction times for feature-based searches in this study were faster than spatial-based searches, suggesting that participants may have perceived a reduced set size in the feature-based condition, masking possible hemifield effects. In three studies we further investigated the extent to which the hemifield advantage is limited to spatial-based search by evaluating the processing of distractors outside the feature and spatial subset of search items (Exp1), characterizing search array preview effects for both feature and spatiala??based search (Exp2), and manipulating spatial certainty of the feature-based search task (Exp3). In all studies, participants searched for a rotated target "T" among distractor "L"s arranged unilaterally or bilaterally in black and white at several eccentricities. Feature-based search participants were told to look only within white search items; spatial-based participants were told to look only in the middle eccentricity. In Exp1 we found that including a target item at an unattended array eccentricity had no effect on search performance for both search conditions. Interestingly, we also found evidence of hemifield independence for both search conditions. In Exp2, RTs for feature-based search were faster, regardless of whether there was a preview; hemifield advantages were only observed for spatial-based search. In Exp3 we controlled for the spatial certainty of the target in both search conditions and found neither faster RTs for feature-based search compared to spatial-based search, or a feature-based hemifield advantage, suggesting that our observation of a hemifield benefit for feature-based search in Exp1 was likely attributable to spatial certainty of where the feature-based target occurred (always in the middle eccentricity). Evidence of hemifield independence persisted for spatial-based search. These results further support the claim that hemifield independence exists exclusively for spatial-based attention.