To investigate the neural mechanisms that humans use to process the ambiguous force measured by the otolith organs, we measured vestibuloocular reflexes (VORs) and perceptions of tilt and translation. One primary goal was to determine if the same, or different, mechanisms contribute to vestibular perception and action. We used motion paradigms that provided identical sinusoidal inter-aural otolith cues across a broad frequency range. We accomplished this by sinusoidally tilting (20 degrees, 0.005-0.7 Hz) subjects in roll about an earth-horizontal, head-centered, rotation axis ("Tilt") or sinusoidally accelerating (3.3 m/s2, 0.005-0.7 Hz) subjects along their inter-aural axis ("Translation"). While identical inter-aural otolith cues were provided by these motion paradigms, the canal cues were substantially different because roll rotations were present during Tilt but not during Translation. We found that perception was dependent on canal cues because the reported perceptions of both roll tilt and inter-aural translation were substantially different during Translation and Tilt. These findings match internal model predictions that rotational cues from the canals influence the neural processing of otolith cues. We also found horizontal translational VORs at frequencies >0.2 Hz during both Translation and Tilt. These responses were dependent on otolith cues and match simple filtering predictions that translational VORs include contributions via simple high-pass filtering of otolith cues. More generally, these findings demonstrate that internal models govern human vestibular "perception" across a broad range of frequencies and that simple high-pass filters contribute to human horizontal translational VORs ("action") at frequencies above approximately 0.2 Hz.

To compare and contrast the neural mechanisms that contribute to vestibular perception and action, we measured vestibuloocular reflexes (VOR) and perceptions of tilt and translation. We took advantage of the well-known ambiguity that the otolith organs respond to both linear acceleration and tilt with respect to gravity and investigated the mechanisms by which this ambiguity is resolved. A new motion paradigm that combined roll tilt with inter-aural translation ("Tilt&Translation") was used; subjects were sinusoidally (0.8 Hz) roll tilted but with their ears above or below the rotation axis. This paradigm provided sinusoidal roll canal cues that were the same across trials while providing otolith cues that varied linearly with ear position relative to the earth-horizontal rotation axis. We found that perceived tilt and translation depended on canal cues, with substantial roll tilt and inter-aural translation perceptions reported even when the otolith organs measured no inter-aural force. These findings match internal model predictions that rotational cues from the canals influence the neural processing of otolith cues. We also found horizontal translational VORs that varied linearly with radius; a minimal response was measured when the otolith organs transduced little or no inter-aural force. Hence, the horizontal translational VOR was dependent on otolith cues but independent of canal cues. These findings match predictions that translational VORs are elicited by simple filtering of otolith signals. We conclude that internal models govern human perception of tilt and translation at 0.8 Hz and that high-pass filtering governs the human translational VOR at this same frequency.

Recovery of GC after vestibular ototoxicity is more commonly observed than recovery of TC. Because ototoxic changes developed and continued in an unpredictable time and manner in relation to ototoxic drug administration, we propose that once ototoxic changes in vestibulo-ocular reflex are detected, ototoxic medications should be discontinued as soon as possible.