Ideal observer for discrimination of the global direction of dynamic random-dot stimuli.
Random-dot cinematograms in which each dot's successive movements are randomly drawn from a Gaussian distribution of directions can produce a percept of global coherent motion in a single direction. Discrimination of global direction was measured for various exposure durations, stimulus areas, and dot densities and bandwidths of the distribution of directions. Increasing the duration produced a greater improvement in performance than did increasing either the area or the density. Performance decreased as the distribution bandwidth increased. An ideal-observer model was developed, and the absolute efficiency for human direction discrimination was evaluated. Efficiencies were highest at large distribution bandwidths, with average efficiencies reaching 35%. A local-global noise model of direction discrimination, based on the ideal-observer model, containing a spatial and temporal integration limit as well as internal noise, was found to fit the human data well. The utility of ideal-observer analyses for psychophysical tasks and the interpretation of efficiencies is discussed.
Watamaniuk
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Department of Psychology, Northwestern University, Evanston, Illinois 60208.
D016002:Discriminant Analysis; D006801:Humans; D008433:Mathematics; D008954:Models, Biological; D009039:Motion Perception / Q000502:physiology*; D010775:Photic Stimulation; D011897:Random Allocation