The initial ocular following responses elicited by apparent-motion stimuli: reversal by inter-stimulus intervals.
Transient apparent-motion stimuli, consisting of single 1/4-wavelength steps applied to square-wave gratings lacking the fundamental ("missing fundamental stimulus") and to sinusoidal gratings, were used to elicit ocular following responses (OFRs) in humans. As previously reported [Sheliga, B. M., Chen, K. J., FitzGibbon, E. J., & Miles, F. A. (2005). Initial ocular following in humans: a response to first-order motion energy. Vision Research, in press], the earliest OFRs were strongly dependent on the motion of the major Fourier component, consistent with early spatio-temporal filtering prior to motion detection, as in the well-known energy model of motion analysis. Introducing inter-stimulus intervals (ISIs) of 10-200 ms, during which the screen was gray with the same mean luminance, reversed the initial direction of the OFR, the peak reversed responses (with ISIs of 20-40 ms) being substantially greater than the non-reversed responses (with an ISI of 0 ms). When the mean luminance was reduced to scotopic levels, reversals now occurred only with ISIs > or=60 ms and the peak reversed responses (with ISIs of 60-100 ms) were substantially smaller than the non-reversed responses (with an ISI of 0 ms). These findings are consistent with the idea that initial OFRs are mediated by first-order motion-energy-sensing mechanisms that receive a visual input whose temporal impulse response function is strongly biphasic in photopic conditions and almost monophasic in scotopic conditions.
Sheliga
B M
BM
Laboratory of Sensorimotor Research, National Eye Institute, National Institutes of Health, Bethesda, MD 20892, USA. bms@lsr.nei.nih.gov
Chen
K J
KJ
FitzGibbon
E J
EJ
Miles
F A
FA
D015350:Contrast Sensitivity / Q000502:physiology; D003623:Dark Adaptation / Q000502:physiology; D005133:Eye Movements / Q000502:physiology*; D005583:Fourier Analysis; D006801:Humans; D008029:Lighting; D009039:Motion Perception / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology; D010775:Photic Stimulation / Q000379:methods; D011597:Psychomotor Performance; D011601:Psychophysics