Little is known about the vestibulo-perceptual (VP) system, particularly after a unilateral vestibular lesion. We investigated
vestibulo-ocular (VO) and VP function in 25 patients with vestibular neuritis (VN) acutely (2 days after onset) and after
compensation (recovery phase, 10 weeks). Since the effect of VN on reflex and perceptual function may differ at threshold
and supra-threshold acceleration levels, we used two stimulus intensities, acceleration steps of 0.5u/s2 and velocity steps of
90u/s (acceleration 180u/s2
). We hypothesised that the vestibular lesion or the compensatory processes could dissociate VO
and VP function, particularly if the acute vertiginous sensation interferes with the perceptual tasks. Both in acute and
recovery phases, VO and VP thresholds increased, particularly during ipsilesional rotations. In signal detection theory this
indicates that signals from the healthy and affected side are still fused, but result in asymmetric thresholds due to a lesioninduced
bias. The normal pattern whereby VP thresholds are higher than VO thresholds was preserved, indicating that any
‘perceptual noise’ added by the vertigo does not disrupt the cognitive decision-making processes inherent to the
perceptual task. Overall, the parallel findings in VO and VP thresholds imply little or no additional cortical processing and
suggest that vestibular thresholds essentially reflect the sensitivity of the fused peripheral receptors. In contrast, a
significant VO-VP dissociation for supra-threshold stimuli was found. Acutely, time constants and duration of the VO and VP
responses were reduced – asymmetrically for VO, as expected, but surprisingly symmetrical for perception. At recovery, VP
responses normalised but VO responses remained shortened and asymmetric. Thus, unlike threshold data, supra-threshold
responses show considerable VO-VP dissociation indicative of additional, higher-order processing of vestibular signals. We
provide evidence of perceptual processes (ultimately cortical) participating in vestibular compensation, suppressing
asymmetry acutely in unilateral vestibular lesions.