Abstract
Previous research on visual search has shown that searching for a target that could be in one of two colors can be very efficient so long as the target and distractor colors are linearly separable (Bauer, Jolicoeur & Cowan, 1996). Thus search for a target among red and yellow distractors is more efficient than to search for a target. However, in those studies the observer was never required to select two target colors from the display simultaneously. Here we employ an “attention to structure” task in which participants make a judgment about the shape of an area defined by one or two colors embedded among two other colors. We find that a visual structure comprised of items among red and yellow items is less readily perceived than a structure composed of items. This clearly shows that it is difficult to select two colors simultaneously even when they are linearly separable from all other colors present. “Attention to structure” tasks can uncover important aspects of visual attention that are not revealed in the visual search task.