The human linear vestibulo-ocular reflex to transient accelerations: visual modulation of suppression and enhancement.
Visual modulation of the linear vestibulo-ocular reflex (LVOR) was investigated in 4 normal subjects exposed to translational interaural transient accelerations of 0.08 g and 0.17 g. Binocular eye movements were recorded with the scleral search-coil technique. LVOR modulation with target proximity was studied using earth-fixed targets at distances of 30 and 60 cm (LVOR-E). LVOR suppression (LVOR-S) was provoked by similar targets which were head-fixed. For both conditions, linear acceleration evoked compensatory slow-phases whose velocities were, from onset, enhanced in proportion to acceleration and target proximity. At 80 ms after motion onset, i.e. before visually-guided eye movements could aid target fixation, gains (eye velocity/relative target velocity) during LVOR-E averaged 0.32 (S.D. 0.07) over all combinations of accelerations and target distances. At this time, eye velocities for LVOR-S were on average 33% lower than for LVOR-E (1.8 degrees/s vs. 2.7 degrees/s). During LVOR-S, a marked suppression of eye movements appeared at 102 ms (S.D. 10 ms). We conclude that mechanisms other than pursuit can be used to attenuate the LVOR at < 80 ms but their effect is weak. The marked suppression observed around 100 ms might be due to an early visual effect on vestibular pathways or by some independent voluntary control mechanism.
Gianna
C C
CC
MRC Human Movement and Balance Unit, National Hospital for Neurology and Neurosurgery, London, UK. claireg@lhs.org
Gresty
M A
MA
Bronstein
A M
AM
D000054:Acceleration; D000222:Adaptation, Physiological; D000328:Adult; D005133:Eye Movements / Q000502:physiology; D006257:Head; D006801:Humans; D008875:Middle Aged; D009038:Motion; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology*; D015348:Vision, Binocular / Q000502:physiology