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Christopher R. L. Cantor, Clifton M. Schor; Flash lag in the frequency domain. Journal of Vision 2002;2(7):29. doi: 10.1167/2.7.29.
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A flashed object presented in spatial alignment with a moving object is generally perceived as lagging behind the moving object. One explanation of this flash-lag effect is the “motion-interpolation” model; the perceived position of the moving object results from interpolation over the path it follows after the occurrence of the flash. An alternative explanation is the “differential-latency” model; the moving stimulus is processed faster than the flash, and thus has traveled some distance beyond the point of the flash when both are perceived together.
In a temporal-order judgment task the abrupt and simultaneous onset of a moving stimulus and a flash is perceived as synchronous (Nijhawan et al. 1999). This is not the case for stimuli with temporal frequency spectra of narrower bandwidth. (I) We used temporal Gabors with a bandwidth of 2 octaves to control the peak temporal frequency of stimuli in a temporal-order judgment task. We found that subjects perceived higher frequency stimuli as delayed relative to lower frequency stimuli. (II) In a moving Vernier task subjects compared the alignment of two identical gratings drifting at equal velocity. We windowed the gratings with Gaussian temporal envelopes differing in bandwidth, so that the gratings ramped on and off and drifted for the period of time in which they were visible. We found a flash-lag effect in Vernier judgments that depends on the difference in the widths of the Gaussian envelopes. The “motion-interpolation” hypothesis does not offer a predicted result for experiment II. Our results are consistent with the hypothesis that greater processing delays exist at higher temporal frequencies.
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