The influence of cognitive tasks on vestibular-induced eye movements in young and older adults.

The purpose of this study was to further investigate the mechanism of the influence of concurrent cognitive tasks on eye movements induced by earth-vertical axis rotation (EVAR) in young and older participants. Ten young (ages 21-34), ten young-old (ages 65-74) and nine older participants (ages 75-84) each performed five different cognitive tasks during sinusoidal EVAR in darkness at 0.02 Hz for three cycles, 0.05 Hz for four cycles, and 0.1 Hz for five cycles, all at a peak velocity of 50 degrees per second. The five tasks differed from one another in terms of their inherent sensory and motor components and were designed to provide insight into the effect of cognitive processing on VOR dynamics. Tasks included auditory frequency and lateralization disjunctive reaction time (DRT) tasks, silent and audible backward counting, and a question-response clinical standard task. For the DRT trials, tones were presented to the participant through earphones. Participants were instructed to respond as accurately and as quickly as possible. Eye movements were recorded with electro-oculography and calibrations were performed before and after every five rotations in all subjects. Participants had an increase in VOR phase lead while performing DRT tasks as compared to the clinical standard and counting tasks. The effect was most noticeable at the 0.02 Hz frequency and was present in all age groups. In addition, we observed a decrease in VOR gain while subjects performed auditory DRT tasks during EVAR at 0.02 Hz, 0.05 Hz and 0.1 Hz as compared to the clinical standard and counting tasks. These results suggest cognitive task-dependent interference between central auditory processing and vestibular processing primarily at the sensory rather than at the motor level.