The purpose of the proposed research is to identify and characterize the mechanisms by which persons with congenital nystagmus perceive a stable visual world, despite uncontrolled rhythmic oscillation of their eyes. Normal eye movements are accompanied by extraretinal signals of changes in eye positions which offset the retinal image motions that occur when the eyes move. These extraretinal signals are often apparently incomplete or absent in persons with nystagmus, indicating that other mechanisms must contribute to perceived visual stability. We suggest that persons with congenital nystagmus suppress visual information during all but a small fraction of each eye movement cycle, akin to the visual suppression that accompanies normal saccades. In addition, we suggest that some persons with nystagmus adapt to the repetitive oscillation of their retinal image, such that image motions produced by the nystagmus are perceptually discounted or ignored. The suppression and adaptation, which we propose contribute to perceived stability in persons with nystagmus, are envisioned to be extensions of mechanisms that also play a part in normal vision. Hence, the results of the studies proposed here to characterize the operation of these mechanisms in persons with nystagmus should improve understanding of how visual stability is achieved during normal eye movements as well as in oculomotor abnormalities such as nystagmus.
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