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Abstract:
Smooth pursuit eye movements add motion to the retinal image. To compensate, the
visual system can combine estimates of pursuit velocity and retinal motion to recover
motion with respect to the head. Little attention has been paid to the temporal
characteristics of this compensation process. Here, we describe how the latency
difference between the eye movement signal and the retinal signal can be measured for
motion perception during sinusoidal pursuit. In two experiments, observers compared the
peak velocity of a motion stimulus presented in pursuit and fixation intervals. Both the
pursuit target and the motion stimulus moved with a sinusoidal profile. The phase and
amplitude of the motion stimulus were varied systematically in different conditions,
along with the amplitude of pursuit. The latency difference between the eye movement
signal and the retinal signal was measured by fitting the standard linear model and a nonlinear
variant to the observed velocity matches. We found that the eye movement signal
lagged the retinal signal by a small amount. The non-linear model fitted the velocity
matches better than the linear one and this difference increased with pursuit amplitude.
The results support previous claims that the visual system estimates eye movement
velocity and retinal velocity in a non-linear fashion and that the latency difference
between the two signals is small.
