Spatially Parallel Processing of Within-Dimension Conjunctions

Abstract

Within-dimension conjunction search for red–green targets amongst red–blue, and blue – green, nontargets is extremely inefficient (Wolfe et al, 1990 Journal of Experimental Psychology: Human Perception and Performance16 879–892). We tested whether pairs of red – green conjunction targets can nevertheless be processed spatially in parallel. Participants made speeded detection responses whenever a red–green target was present. Across trials where a second identical target was present, the distribution of detection times was compatible with the assumption that targets were processed in parallel (Miller, 1982 Cognitive Psychology14 247–279). We show that this was not an artifact of response-competition or feature-based processing. We suggest that within-dimension conjunctions can be processed spatially in parallel. Visual search for such items may be inefficient owing to within-dimension grouping between items.