The perception of translational motion: what is vestibular and what is not.

In response to translations of the head, the linear vestibulo-ocular reflex (LVOR) produces compensatory eye movements that are high-pass in nature, with a declining response magnitude and an increasing phase lead with declining stimulus frequency. Perception of head translation, however, is reported to be robust at much lower frequency than predicted by the LVOR, causing speculation that the vestibular processing underlying reflex and perceptual responses are different. Direct comparison of these two responses across a large frequency range proves problematic, in part because of difficulties encountered in the assessment of perception at high frequency, and confounding variables at low frequency. We used innovative techniques to measure psychophysical responses to translation, and find strong similarity to the LVOR. These include experiments in which motion cues were limited to those of an inertial nature, and conclude that the vestibular system comprises only one input to perceptual mechanisms related to linear motion, and this is supplemented (particularly at low frequency) by somatic and cognitive cues.