title: Optimal observer model of single-fixation oddity search predicts a shallow set-size function.
abstract: A common finding in oddity search, a search in which the target is unknown but defined to be different from the distractors, is that human performance remains insensitive or even improves with number of distractors (set size). A number of explanations based on perceptual and attentional mechanisms have been proposed to explain the anomalous set-size effect. Here, we consider whether the shallower set-size function for oddity search could be explained by stimulus information and task demands. We developed an ideal-observer and a difference-coding (standard-deviation) model for single-fixation oddity search and compared it to the ideal observer in the standard target-known search as well as to human performance in both search tasks. Performance for the ideal and difference-coding model in the oddity search resulted in a shallower set-size function than the target-known ideal observer and was a good predictor of human search accuracy. However, the ideal-observer model was a better predictor than the standard-deviation model for 10 of the 12 data sets. The results highlight the importance of using ideal-observer analysis to separate contributions to human performance arising from perceptual/attentional mechanisms inherent to the human brain from those contributions arising from differences in stimulus information associated with the tasks.
authors.affiliation: Department of Psychology, University of California, Santa Barbara, CA 93106, USA. schoonveld@psych.ucsb.edu
authors.forename: Wade
authors.initials: W
authors.lastname: Schoonveld
authors.forename: Steve S
authors.initials: SS
authors.lastname: Shimozaki
authors.forename: Miguel P
authors.initials: MP
authors.lastname: Eckstein
mesh_terms: D000328:Adult; D001288:Attention; D004192:Discrimination, Psychological; D005260:Female; D005403:Fixation, Ocular; D006801:Humans; D008960:Models, Psychological; D009949:Orientation; D010364:Pattern Recognition, Visual; D011237:Predictive Value of Tests; D017603:Signal Detection, Psychological; D014796:Visual Perception