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Christopher R. L. Cantor, Clifton M Schor; Velocity dependence of the Flash Lag Effect for narrowband stimuli — is it linear?. Journal of Vision 2003;3(9):211. doi: 10.1167/3.9.211.
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We identify two predictions of linear velocity dependence of the Flash Lag Effect (FLE) and demonstrate that they do not hold for narrowband stimuli at low velocities.
Most investigations of the FLE employ high velocity broadband stimuli, such as lines or dots with sharp boundaries and flashes with rapid onset and offset (e.g. Nijhawan 1994; Baldo & Klein 1995; Purushothaman et al, 1998; Krekelberg & Lappe 1998; Eagleman & Sejnowski, 2000; Whitney & Cavanagh 2000; Murakami 2001). The perceived spatial lag of the flash is usually reported to increase linearly with the velocity of the moving stimulus and is often quantified as an equivalent temporal delay of fixed magnitude.
Last year, we introduced a different paradigm to permit the study of FLE in narrow-band stimuli moving at considerably slower velocities (Cantor & Schor VSS 2002). We found FLE in moving-vernier tasks where drifting sine-wave stimuli were windowed with Gaussian temporal envelopes of different bandwidth. In each experiment, the stimuli had energy focused around a single spatial and temporal frequency pair (SF, TF). Both gratings had identical SF, but the “flashed” grating was smeared in TF so that it contained more energy at higher and lower TF than the “moving” grating.
We consider the FLE as measured over a range of the SF-TF pairings that define our narrow-band stimuli. Linear velocity dependence offers two predictions. I. For stimuli of identical velocity (but different SF and TF), FLE will remain constant. II. Perceived delay will scale linearly with increases in the velocity of the stimulus.
These two predictions were not substantiated. We conclude that the magnitude of the flash lag effect in narrowband stimuli does not depend on the velocity, but rather a more complicated relationship between the spatial and temporal frequency content of the stimulus.
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