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Hideko F. Norman, J. Farley Norman, Kristina F. Pattison, Amy E. Craft, Elizabeth Y. Wiesemann, M. Jett Taylor; The role of explicit and implicit standards in speed discrimination. Journal of Vision 2008;8(6):606. doi: 10.1167/8.6.606.
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© ARVO (1962-2015); The Authors (2016-present)
Five experiments investigated speed discrimination. Variations of the method of constant stimuli were used to obtain speed discrimination thresholds in Experiments 1, 2, 4, and 5, while the method of single stimuli was used in Experiment 3. The observers' thresholds were significantly influenced by the choice of psychophysical method and by changes in the standard speed. The observers' judgments were unaffected, however, by changes in the magnitude of random variations in stimulus duration. When an implicit standard was used, the observers produced relatively low discrimination thresholds (7.0 percent of the standard speed), replicating the results of McKee (1981). When an explicit standard was used in a 2AFC variant of the method of constant stimuli, however, the observers' discrimination thresholds increased by 74 percent (to 12.2 percent), similar to the thresholds obtained by Mandriota, Mintz, & Notterman (1962). A subsequent signal-detection analysis revealed that the observers' actual sensitivities to differences in speed were in fact equivalent for both psychophysical methods. The formation of an implicit standard in the method of single stimuli allows observers to make judgments of speed that are as precise as those obtained when explicit standards are available.
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