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Michael J Disch, Karen K Valois, Tatsuto Takeuchi; Speed perception of flickering stimuli. Journal of Vision 2003;3(9):395. doi: https://doi.org/10.1167/3.9.395.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To examine how accurately observers can judge the speed of an intermittently presented linearly translating spot. Methods: Stimuli were moving white spots (0.3 deg, 5 cd/m2) on a dark background. Test stimuli moved at a constant velocity, but flickered on and off as they moved across the screen. Comparison stimuli moved at a constant velocity without flickering. Angular velocity of the test stimuli ranged from 4 deg/sec to 32 deg/sec at octave intervals. Test stimuli flickered at 2, 4, 8, or 16 Hz as square wave alternations. Subjects compared the forward speeds of translation of the two stimuli. An interleaved 2AFC staircase method was used to determine the comparison stimulus speed that appeared to match the translation speed of the flickering spot. Direction of motion (left/right) and spatial position (upper/lower) of test and comparison stimuli were randomized on each trial. The distance traveled and starting location of each stimulus varied pseudorandomly. Results: The perceived speed of the test stimuli varied as a function of velocity and flicker rate. In general, the speed of flickering stimuli moving at a slow velocity (4 deg/sec) was either overestimated or accurately matched. Moderate and high velocities (8–32 deg/sec) tended to be underestimated, with the error increasing with increasing velocity. At the highest flicker frequency (16 Hz), the apparent speed of translation was consistently greater than for lower flicker frequencies. Conclusion: The perceived speed of intermittently presented stimuli depends upon both translation velocity and flicker rate, with slow velocities and fast flicker rates producing speed overestimation, while fast velocities and slow flicker rates lead to speed underestimation.
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