Eye Movements Induced by Linear Acceleration are Modified by Visualisation of Imaginary Targets

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Abstract
Lateral eye movement responses to linear acceleration in the lateromedial axis of the head have been examined in normal human subjects who were seated within a cabin, free to move on a horizontal linear track. The motion stimulus was either sinusoidal (0.2–0.8 Hz) or pseudo-random (0.11–1.25 Hz) in form, with a peak acceleration of 1.5 m.s‐2. In darkness, while carrying out mental arithmetic, the mean ratio of slow-phase eye velocity to linear cart velocity increased from 2.8d`/m at 0.2 Hz to 10.5d`/m at 0.8 Hz during sinusoidal stimulation. When subjects were instructed to imagine a near head-fixed target in darkness, eye velocity decreased by 25%–48% during both sinusoidal and pseudo-random stimulation. When subjects were instructed to visualise an earth-fixed target during sinusoidal stimulation eye velocity was augmented by 47 % when imagining a target 3 m distant and by 175% when visualising a target 0.6 m distant. Response augmentation was not as great during pseudo-random stimulation. The results indicate that the otolith-ocular response is highly modifiable by mental set.