Visual-vestibular stimulation influences spatial and non-spatial cognitive processing.

This study investigated the impact of visual-vestibular stimulation on performance of an auditory information processing task in young and older adults. Performance on a spatial choice reaction time task was compared to performance on a non-spatial choice reaction time task. The tasks were performed during simultaneous rotational and moving visual stimulation. The non-spatial task was an auditory frequency discrimination task while the spatial task was a right-left lateralization task. Visual and vestibular conditions consisted of a non-movement baseline, sinusoidal earth-vertical axis rotation (EVAR) in darkness, off-vertical axis rotation (OVAR) in darkness at a constant velocity, OVAR in darkness with a sinusoidal profile, EVAR with a lighted visual surround, constant velocity optokinetic stimulation, and sinusoidal optokinetic stimulation. Baseline reaction times were subtracted from reaction times during each stimulus condition to yield "task cost", which was analyzed statistically. Subjects were healthy young (n=20; 24 ± 2.7 yrs; 10F) and older (n=29; 73 ± 6.0 yrs; 18F) adults. Results indicated that task cost was affected by the visual-vestibular condition and a task x condition interaction. There was no main effect of task or age group and no significant interaction with age. Otolithic stimulation and visual stimulation were associated with greater task cost compared to semicircular canal stimulation. Combining semicircular canal with otolithic or visual stimulation had no additional effect beyond otolithic or visual stimulation alone. This pattern of task cost being larger for otolith or visual vs. semicircular canal stimulation was found for both the spatial and non-spatial tasks. The significant interaction between condition and task type revealed that the task cost for the spatial task was larger than the task cost for the non-spatial task during visual conditions but not during non-visual conditions although the visual and non-visual conditions were not entirely comparable. This study suggests that interference of vestibular stimulation with cognitive processing is especially prominent for otolithic and visual stimulation although the strength of the various visual-vestibular stimuli may not have been uniform. Also, spatial tasks are more affected than non-spatial tasks during visual stimulation and interference between vestibular stimulation and cognitive processing is not age dependent for these relatively easy tasks.