Perceptual Influences of Extraretinal Signals for Normal Eye Movements and Infantile Nystagmus

Abstract

Abstract The involuntary eye movements in patients with infantile Nystagmus (IN) generate rapid to-and-fro motion of the retinal image, which has the potential to produce oscillopsia and the perception of motion smear. In normal subjects, extraretinal signals can neurally “cancel” the retinal image motion that occurs during eye movements and can reduce the extent of perceived motion smear. Previous studies indicate that extraretinal signals also contribute to perceived stability in subjects with IN. In addition to “canceling” the to-and-fro motion of the retinal image, extraretinal signals also partly compensate for changes in retinal-image orientation that occur during the torsional component of IN. We show that extraretinal signals reduce perceived motion smear in subjects with IN, preferentially for relative target motion in the opposite direction of slow-phase eye movements. A possible mechanism for the reduction of perceived motion smear is a decrease in the duration of the temporal impulse response function during eye movements. Temporal contrast sensitivities measured in normal observers, and subjects with IN are consistent with this possibility. Although extraretinal eye movement signals have similar influences on perceived stability and clarity in normal observers and subjects with IN, the characteristics of the operative neural mechanisms may not be identical.