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Laurent Madelain, Anna Montagnini, Guillaume Masson; Transient contrast-induced perceived-velocity perturbations and smooth pursuit: tracking the footstep illusion. Journal of Vision 2013;13(9):384. doi: 10.1167/13.9.384.
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© ARVO (1962-2015); The Authors (2016-present)
At slow target velocities, there is a linear increase in smooth pursuit eye velocity gain with increasing contrast, a phenomenon which supports the assumption that perceptual and motor responses are driven by a shared signal: low-contrast stimuli consistently appear slower than the same targets presented at higher contrast. The "footstep" illusion is based on these perceived changes in target velocity. Here we ask whether one may use the footstep illusion to probe the effects of transient perceived-velocity perturbations on smooth pursuit in the absence of perturbation in the target’s position signal. Three subjects peri-foveally tracked a bright yellow horizontal bar translating over a black-and-white grating. On high luminance trials the translating yellow bar’s luminance contrast was 1% and 100% with respect to the white and black stripes respectively, whereas on control trials, the luminance contrast of the stimulus was 50% with respect to all stripes. Luminance contrast varied at 2, 2.5 or 3Hz, depending on the target velocity and on the grating spatial frequency. We found that in the high luminance trials, pursuit velocity gain was oscillating at a frequency locked to the contrast’s frequency indicating that eye velocity was well controlled by the local luminance contrast. In a second experiment, the paradigm was identical except that the yellow bar first had a low luminance (50% contrast). At a variable point of time in the trial, the luminance increased for 500 ms (1% and 100% luminance contrast) before returning to the low luminance level. We found a strong transient response in velocity gain when the luminance transiently changed. These results extend previous work on the effects of luminance contrast on smooth pursuit and provide a new tool to selectively and transiently perturb pursuit eye velocity in the absence of perturbation in the target position.
Meeting abstract presented at VSS 2013
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