Visual control of postural orientation and equilibrium in congenital nystagmus

PURPOSE. TO investigate how humans with congenital nystagmus (CN) use visua l information to stabilize and orient their bodies in space. METHODS. Center of foot pressure (COP) and head displacements in the latera l plane were recorded using a sway platform and Schottky barrier photodetec tor, respectively. In experiment 1, a comparison was made of the oscillator y characteristics of body sway with eyes open compared with eyes closed. Ex periment 2 studied the postural readjustments made in response to absolute or relative motion (motion parallax) of objects in the visual scene, genera ted by lateral displacement of background scenery. RESULTS. Experiment 1 revealed that subjects with CN were not able to use v isual information to stabilize COP but were able to stabilize the head at f requencies lower than 1 Hz. Experiment 2 showed that in response to the dis placement of a visual display, for both absolute motion and motion parallax , subjects with CN reoriented their body in space in a manner similar to co ntrol subjects. CONCLUSIONS. The results suggest that despite involuntary eye movements, su bjects with CN use orientation cues to control their posture, but not dynam ic cues useful to control the rapid oscillations that are particularly impo rtant at the lever of COP. These findings suggest that in CN, visual contro l of posture is restricted by low-frequency sampling of the visual scene.