Simple Shapes Guide Visual Attention Based on Their Global Outline or Global Orientation Contingent on Search Goals

Public Significance Statement This study shows that when we search for a two-dimensional object, its shape can be used to guide our visual attention so that we can efficiently find the object. In contrast, oriented edges of such a two-dimensional object are not sufficient to explain successful search for shapes. Whether the orientation of a shape is also used to guide attention depends on the shape itself and on the necessities imposed by the search context. It is still unclear which features of a two-dimensional shape (e.g., triangle, square) can efficiently guide visual attention. Possible guiding features are edge orientations (single oriented shape edges; e.g., verticals during search for squares), global outlines (combination of the target edges; e.g., squares), or global orientations (specific orientations of global outlines; e.g., squares but not diamonds). Using a contingent-capture protocol, we found evidence for task-dependent guidance by the global shape outline and the global shape orientation. First, if participants searched for a shape (an equilateral triangle) independent of its pointing direction, cues with the same global shape outline as the target captured attention, even without sharing any edge orientations with the target. Second, however, if a shape's specific pointing direction was task-relevant, attentional guidance changed to the specific orientation of the global shape. Our results show that the global shape outline and the global shape orientation can both guide visual attention, contingent on the nature of the shape and the current search goals. We discuss differences between shapes (equilateral triangles and isosceles trapezoids) considering models of shape perception and conclude with a critical review of the contingent-capture protocol as a complementary method to visual search protocols.