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E. Hiris; Limits on the perception of transparency from motion. Journal of Vision 2001;1(3):377. doi: 10.1167/1.3.377.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: When spatially intermingled sets of dots move in different directions, observers often report perceiving two or more transparent motion directions. I sought to determine the maximum number of motion directions participants report in moving dot displays. Methods: Twenty-eight naive participants viewed random-dot cinematograms containing from one to nine motion directions for .2, 1, or 5 seconds. Immediately after the display disappeared, participants indicated the number of directions presented. Participants received no feedback regarding the accuracy of their responses. Results: Participants easily judged the number of directions in the random-dot cinematogram when there were one or two directions presented. The maximum number of directions accurately perceived was three or four, with longer display durations yielding better performance. In an additional study, non-naive participants provided data from separate blocks of trials collected over several days. Accuracy improved over blocks for displays with more than three motion directions, however, performance did not exceed 70% correct, regardless of display duration. Conclusions: Accurately perceiving segmented motion directions from spatially intermingled dots was limited to three or four distinct directions. Extended practice, longer display durations, and knowledge of how the displays were constructed improved performance, but to a limited extent. The visual system may be fundamentally limited to segmenting three or four motion directions from spatially intermingled moving dots.
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