Visual information potentiates incremental VOR adaptation.

introductionVestibulo-ocular reflex (VOR) response to a given head rotation can be modified through adaptation by inducing a visuo-vestibular mismatch. Incremental velocity error protocols allow for rapid unilateral VOR adaptation in the everyday-life range of head movement high velocities. However, these protocols are conducted in darkness, with the sole visual stimulation of the central retina being provided by the fixated target. This study aimed to investigate whether enhanced visual information can improve incremental VOR adaptation, starting with an assessment of the feasibility to implement the incremental velocity error adaptation protocols within a virtual reality environment.

methodsEighteen participants with normal vestibular function were recruited. Two different visual conditions were designed for adaptation: (1) a Uniform condition where a red fixation dot was the only salient cue displayed within a grey void, emulating the original Incremental Velocity Error protocol, and (2) an Enriched condition where the fixation dot was overlayed on a structured natural visual environment. Participants performed both conditions in two sessions separated by at least three days, following a randomly assigned order and side of adaptation. During the adaptation phase, unilateral passive head impulses were performed while the participant fixated the dot with a progressively increasing visuo-vestibular mismatch: the gain of visual feedback (dot and background) increased by 0.1 every 30 head impulses, from the normal unity gain until a gain demand of 2 was reached (visual scene rotation twice as large as the head movement). Pre- and post-adaptation VOR gain was measured during head impulse testing in dark.

resultsIn the Uniform condition, the mean VOR gain was significantly higher after adaptation compared to before (1.41 in Post vs. 1.14 in Pre, p < 0.001). There was no significant difference between pre-adaptation VOR gains measured in darkness between the Uniform and Enriched conditions (respectively 1.14 and 1.11, t = 1.331, p = 0.201). But importantly, there was a significant interaction between condition (Uniform vs. Enriched) and phase (Pre vs. Post) (F = 13.163, p = 0.002) with a 32.5% VOR gain increase in the Enriched condition compared to a 24.1% VOR gain increase in the Uniform condition. No significant changes in post-adaptation VOR gain were observed on the contralateral side in either condition.

conclusionVirtual reality can be used to induce VOR adaptation using Incremental Velocity Error protocols. Moreover, using an enriched visual environment for inducing the visuo-vestibular mismatch potentiates VOR gain adaptation.