OBJECT GROUPING CONTINGENT UPON BACKGROUND

This study analyzes grouping between singletons (line elements popping out by orientation gradient) when they segregate from textures of uni formly 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 ba sed on local processing. (ii) Spatial interactions between parallel si ngletons are present at short distances and reduce discrimination. (ii i) An interruption of background how (directed along the orientation o f background line elements) produced by the grouped pattern when ortho gonal to it, enhances discrimination; this effect is present at both s hort and large distances between singletons, indicating a global proce ss. (iv) Spatial interactions are present between parallel singletons even at large distances and independently of background orientation, s uggesting that grouping generates a figural contest within which featu res to be bound together interact. Moreover, flow interruption and fig ural context were absent in a detection task, thereby suggesting their specific involvement in grouping and figure binding. Overall, the res ults may indicate that grouping operates on already segmented line ele ments, across different orientations and over both short and long dist ances in between. (C) 1997 Elsevier Science Ltd.