Abstract
What object properties warrant selection by object-based attention? Previous research has suggested that uniformity is required for object-based attentional selection (Watson & Kramer, 1999), yet non-uniform objects are encountered frequently. In the current experiments, we investigated the interplay between uniformity and part-boundaries, as well as their effect on object-based attentional selection. Specifically, we asked if attention can select non-uniform objects under appropriate circumstances. If so, then objects with regions that are dissimilar in color may be selected as easily as uniform objects when uniformity changes occur at the part-boundary. Using a modified object-based attention task (see Egly et al., 1994; Vecera, 1994), observers viewed two outline rectangle stimuli, each with a different contour color on either half (Experiment 1). No object-based attention effects were found, indicating that object-based attention did not select the non-uniform rectangles. To address the potential interplay between uniformity and part-boundaries, we used two-part objects (hourglass-shaped objects) and manipulated surface uniformity. In Experiment 2, strictly uniform surfaces were used to ensure object-based attention could select these hourglasses. For the remaining experiments, the hourglasses had a different color on either half with the change occurring at the part boundary (Experiment 3), with the color change shifted off the part-boundary (Experiment 4A), or with the part-boundary shifted and the color change occurring precisely halfway through the objects (Experiment 4B). Object-based effects were only found for Experiment 2, suggesting that attention can only select non-uniform objects when the change occurs at a part-boundary.
NSF grant BCS 03-39171 awarded to Shaun P. Vecera