Object grouping contingent upon background.

Abstract

This study analyzes grouping between singletons (line elements popping out by orientation gradient) when they segregate from textures of uniformly oriented line elements. In the first experiment three adjacent singletons formed a texture bar; in the second experiment the distance between two singletons to be grouped was manipulated. The observer's task was to discriminate the orientation of the global pattern made by the singletons. The results and the explanations suggested are that: (i) an inner gradient within the texture bar (when the singletons are reciprocally orthogonal) operates only at short distances and enhances discrimination, indicating an initial stage of texture segregation based on local processing. (ii) Spatial interactions between parallel singletons are present at short distances and reduce discrimination. (iii) An interruption of background flow (directed along the orientation of background line elements) produced by the grouped pattern when orthogonal to it, enhances discrimination; this effect is present at both short and large distances between singletons, indicating a global process. (iv) Spatial interactions are present between parallel singletons even at large distances and independently of background orientation, suggesting that grouping generates a figural context within which features to be bound together interact. Moreover, flow interruption and figural context were absent in a detection task, thereby suggesting their specific involvement in grouping and figure binding. Overall, the results may indicate that grouping operates on already segmented line elements, across different orientations and over both short and long distances in between.