Response of the human vestibulo-ocular reflex following long-term 2x magnified visual input

This study examines the contribution of predictive motor programming to the adjustment of vestibulo-ocular reflex (VOR) gains after exposure to spectacles with a 2X magnification. When fully adapted, subjects exhibited two-fold gain increases with a 3 Hz sinewave stimulus with both an imaginary earth-fixed and imaginary moving target. Before complete adaptation was achieved, quick phases embedded in the slow component were observed intermittently which compensated for insufficient VOR gain. At 0.5 Hz in the same state of full adaptation during fixation of an imaginary earth-fixed target subjects exhibited a gain increase of only approximately 75% indicating that the contribution of VOR adjustment is not sufficient for perfect visual stabilization at lower frequencies. Over the range of random stimulation (0.5-5 Hz), the VOR failed to exhibit complete adaptation. The degree of adaptation derived with a VOR-cancellation task was less overall than that with a task requiring perfect compensatory eye movements. These findings indicate that central motor programmes are required in the adaptive process to achieve visual stability.