title: Information-limited parallel processing in difficult heterogeneous covert visual search.
abstract: Difficult visual search is often attributed to time-limited serial attention operations, although neural computations in the early visual system are parallel. Using probabilistic search models (Dosher, Han, & Lu, 2004) and a full time-course analysis of the dynamics of covert visual search, we distinguish unlimited capacity parallel versus serial search mechanisms. Performance is measured for difficult and error-prone searches among heterogeneous background elements and for easy and accurate searches among homogeneous background elements. Contrary to the claims of time-limited serial attention, searches in heterogeneous backgrounds instead exhibited nearly identical search dynamics for display sizes up to 12 items. A review and new analyses indicate that most difficult as well as easy visual searches operate as an unlimited-capacity parallel analysis over the visual field within a single eye fixation, which suggests limitations in the availability of information, not temporal bottlenecks in analysis or comparison. Serial properties likely reflect overt attention expressed in eye movements.
authors.affiliation: Memory, Attention, Perception MAP Laboratory, Department of Cognitive Sciences, Institute of Mathematical Behavioral Science, University of California, Irvine 92697-5100, USA.
authors.forename: Barbara Anne
authors.initials: BA
authors.lastname: Dosher
authors.forename: Songmei
authors.initials: S
authors.lastname: Han
authors.forename: Zhong-Lin
authors.initials: ZL
authors.lastname: Lu
mesh_terms: D001288:Attention; D015350:Contrast Sensitivity; D004192:Discrimination, Psychological; D005403:Fixation, Ocular; D006801:Humans; D008960:Models, Psychological; D015233:Models, Statistical; D009949:Orientation; D010364:Pattern Recognition, Visual; D010470:Perceptual Masking; D011601:Psychophysics; D012858:Size Perception; D014794:Visual Fields