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Michael Disch, Karen De Valois; Effects of flicker on perceived object velocity. Journal of Vision 2007;7(9):39. doi: 10.1167/7.9.39.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To examine perceived speed for objects which flicker as they move. Methods: Stimuli were luminance defined spots (0.45 deg, 30 cd/m2 time-averaged luminance) on a dark background. Test stimuli flickered and moved at a constant velocity. Chromatic conditions included isoluminant flicker along either the LM or S axes. Chromatic contrasts were 8%, 15.3%, and 80% for the L, M, and S cones respectively. Luminance flicker conditions included Michelson contrasts of 10.5%, 20%, 40%, and 80%. Angular velocity of 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. Comparison stimuli moved at a constant velocity without flickering. Subjects compared the forward speeds of translation of the two stimuli. An interleaved 2AFC staircase method determined the comparison stimulus speed that appeared to match the translational speed of the flickering spot. Direction of motion (left/right) and spatial position (upper/lower) of the two stimuli were randomized on each trial. Stimulus travel distance and starting location varied pseudorandomly. Results: Perceived speed was minimally affected by chromatic flicker. S axis flicker led to greater speed biases than did LM axis flicker, however, overestimations never exceeded 4%, and were generally lower or non-existent. Overestimation was maximal for slowly moving objects with low flicker rates and quickly moving objects with high flicker rates. Luminance flicker at 8 and 16 Hz produced small speed overestimations, no greater than 6%, for quickly moving objects in the 80% contrast condition only. Underestimation was not found. Conclusion: Object based flicker for a constantly visible object has small effects on perceived speed. The greatest bias was seen for quickly moving objects with high flicker rates. However, research we conducted previously found more substantial perceived speed biases for luminance defined objects whose visibility was spatially sampled.
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