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Lili Shen, Robert Allison, Laurie Wilcox, Yoshitaka Fujii; Motion discrimination of high frame rate movie. Journal of Vision 2014;14(15):57. doi: 10.1167/14.15.57.
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Recently high-frame rate movie technology has received significant technical and artistic attention due to its potential to present higher-fidelity motion to cinemagoers. Speed discrimination is a well-studied psychophysical task used to quantify sensitivity to motion. We used speed discrimination as a measure of the effects of frame presentation protocol on motion perception. An interleaved staircase procedure was used with a 2-interval-forced-choice task to measure discrimination thresholds for 7 subjects. The independent variables were frame rate and motion speed for a high-contrast line target. Flash (refresh) rate was fixed at 96 Hz and different frame rates were produced by updating the frame every refresh (single flash, 96 fps), alternate refresh (double flash, 48 fps) or every fourth refresh (quadruple flash, 24 fps). Stimuli were presented binocularly on CRT displays in a Wheatstone stereoscope but the presentation protocols approximate standard film presentation protocols. Five velocities (4deg/s, 8deg/s, 16deg/s, 32deg/s and 64deg/s) were tested in separate blocks of trials; within a block staircases for the three flash protocols were randomly interleaved. The results show that at speeds greater than 16deg/s, discrimination thresholds decrease with increasing frame rate (or equivalently, increase with number of repeated frames for a given flash protocol). This improvement likely reflects sensitivity to motion artifacts at low frame rates, when frames are repeated multiple times. Thus this study confirms that observers are sensitive to the improved fidelity offered by higher frame rates over the range considered for high frame rate cinema (24–96 fps).
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