title: Search asymmetry: a diagnostic for preattentive processing of separable features.
abstract: The search rate for a target among distractors may vary dramatically depending on which stimulus plays the role of target and which that of distractors. For example, the time required to find a circle distinguished by an intersecting line is independent of the number of regular circles in the display, whereas the time to find a regular circle among circles with lines increases linearly with the number of distractors. The pattern of performance suggests parallel processing when the target has a unique distinguishing feature and serial self-terminating search when the target is distinguished only by the absence of a feature that is present in all the distractors. The results are consistent with feature-integration theory (Treisman & Gelade, 1980), which predicts that a single feature should be detected by the mere presence of activity in the relevant feature map, whereas tasks that require subjects to locate multiple instances of a feature demand focused attention. Search asymmetries may therefore offer a new diagnostic to identify the primitive features of early vision. Several candidate features are examined in this article: Colors, line ends or terminators, and closure (in the sense of a partly or wholly enclosed area) appear to be functional features; connectedness, intactness (absence of an intersecting line), and acute angles do not.
authors.forename: A
authors.initials: A
authors.lastname: Treisman
authors.forename: J
authors.initials: J
authors.lastname: Souther
mesh_terms: D000328:Adult; D001288:Attention; D003118:Color Perception; D004193:Discrimination Learning; D004292:Dominance, Cerebral; D005260:Female; D005556:Form Perception; D006801:Humans; D008297:Male; D009949:Orientation; D014796:Visual Perception