Adaptive Control of Saccade Metrics

Applying optical aids distorts the relationship established between the visual signals impinging on the retina and our “model of the outside world” by which we plan directed motor activity such as hand or head movements toward an object. So, putting on magnifying or reducing spectacles raises a serious problem for the performance of the vestibuloocular reflex (VOR), which takes a nonvisual signal derived from the semicircular canals to compensate for retinal slip otherwise induced by head turns. The VOR gain becomes inappropriate, and this results, perceptually, in perceived instability of the visual world, eventually causing nausea. Fortunately, these initial problems disappear rapidly, within a few hours or days. An important factor for this kind of habituation is the capacity of the VOR gain for adaptive recalibration, as has been investigated in numerous studies (e.g., Miles and Fuller, 1974; Miles and Eighmy, 1980).