Translational motion perception and vestiboocular responses in the absence of non-inertial cues.

Path integration studies in humans show that we have the ability to accurately reproduce our path in the absence of visual information. It has been suggested that this ability is supported by acceleration signals, as transduced by the otolith organs, which may then be integrated twice to produce path excursion. Vestibuloocular responses to linear translations (LVOR), however, show considerable frequency dependence, with substantial attenuation in response to low frequency translational motion. If otolith information were processed similarly by path integration mechanisms, the resulting signal would not be sufficient to account for robust path integration for stimuli typically used in such studies. We hypothesized that such behavior relies upon cognitive skill and transient otolith cues, typically combined with non-directional cues of motion, such as vibration and noise produced by the mechanics apparatus used to produce linear motion. Continuous motion estimation tasks were used to assess translation perception, while eye movement recordings revealed LVOR responses, in 12 normal and 2 vestibulopathic human subjects while riding on a sled designed to specifically minimize non-directional motion cues. In the near absence of such cues, perceptual responses, like the LVOR, showed high-pass characteristics. This implies that otolith signals are not sufficient to support previously observed path integration behaviors, which must be supplemented by non-directional motion cues.