Abstract
Abstract: :
Purpose: The rotational vestibulo–ocular reflex (RVOR) is an eye rotation directed opposite to the head to maintain a constant gaze position. When the head is moved to pursue a target, the RVOR must be cancelled or substantially decreased so that fixation remains on the target. At head movement/target frequencies less than about 1Hz, RVOR cancellation is relatively efficient. However, at frequencies of 1Hz and above, drifting vestibular eye movements opposite to the head movements occur. The purpose of this experiment was to determine if subjects could be trained to cancel the RVOR during eye–head pursuit at a head movement/target frequency (1Hz) where RVOR cancellation is typically inefficient. Methods: 9 subjects participated. The right eye was patched, and then subjects tracked a red laser spot moving horizontally in a sinusoidal manner (distance:3.4m, frequency:1Hz, amplitude:10° ) with the head. In the first 3 trials, subjects tracked the target with the head and they were encouraged to minimize smearing of the target. In the next 15 trials, a rectangular aperture (3.3°) was mounted 87mm in front of the left eye. Subjects then tracked the target while trying to maintain a view of the laser through the aperture. In the final 3 trials, the aperture was removed and subjects tracked the target with the head. In these final trials, subjects were encouraged to apply the same eye–head tracking strategy as that used with the aperture. Head position was measured with a magnetic coil and eye position was measured with a limbal tracker.Results: The extent of RVOR cancellation was determined by calculating the standard deviation of eye position. A lower standard deviation indicated greater RVOR cancellation. The mean standard deviation for the first 3 trials (no aperture) was 3.6°±1.4°, the mean standard deviation for the final trial with the aperture was 2.0°±0.6°, and the mean standard deviation for the final 3 trials (no aperture) was 3.0°±0.9°. Pairwise comparisons of these means showed that only the means for the first 3 trials and for the final trial with the aperture were significantly different. Conclusions: RVOR cancellation was most efficient with the aperture. Thus, if given visual feedback about eye position such as that provided by the aperture, subjects rapidly learn to cancel the RVOR at a frequency where this cancellation is normally difficult. However, the RVOR cancellation learned in the presence of visual feedback only leads to modest improvements in RVOR cancellation when this feedback is removed. Longer training sessions with the aperture may lead to greater improvements in RVOR cancellation in situations with and without visual feedback.
Keywords: vestibulo–ocular reflex • eye movements: conjugate • eye movements: saccades and pursuits