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Comparisons between the visual performance of persons with congenital nystagmus (CN) and normal observers under conditions of similar retinal image motion reveal the extent to which the nystagmus-induced image motion determines visual functioning and perception in CN. Visual acuity undergoes similar changes with the characteristics of retinal image motion in normal observers and persons with CN. However, acuity is poorer than expected on the basis of the image motion in some individuals with CN, suggesting an additional sensory deficit. When presented with visual stimuli that simulate the retinal image motion in CN, normal observers perceive substantial target movement and motion smear. In contrast, most individuals with CN perceive the visual world to be stable and relatively clear. These dramatic perceptual differences are attributed primarily to the visual consequences of extra-retinal signals, which have been shown to accompany the involuntary eye movements in CN as well as the voluntary and involuntary eye movements in normal observers. Adaptation to periodic motion of the retinal image may also contribute to the perception of stability in persons with CN. The data presented in this paper indicate that, on the whole, largely similar visual mechanisms are likely to underlie visual functioning and mediate perception in persons with CN and normal vision.