An Ideal Observer for Discrimination of the Global Direction of Dynamic Random Dot Stimuli

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Extended the ideal-observer analysis to discrimination of global direction produced by dynamic random-dot cinematograms. Ss were 3 experienced observers, including the author. 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.



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