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Wade Schoonveld, Steve S. Shimozaki, Miguel P. Eckstein; Optimal observer model of single-fixation oddity search predicts a shallow set-size function. Journal of Vision 2007;7(10):1. doi: 10.1167/7.10.1.
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© ARVO (1962-2015); The Authors (2016-present)
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.
Note: *Probability of observing the data given the model <.01%.
Note: *Probability of observing the data given the model <.01%. Values in boldface highlight the conditions and observers for which the standard-deviation model fit better than the ideal-observer model.
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