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Abstract

Most of the previous literature regarding eye movements use visual stimuli alone. However, in real life, visual and auditory stimuli occur together frequently. It has been shown that a sound presented just before or simultaneously with the visual target reduces the latency of the saccades. The present study investigates the effect of a sound presented shortly before the LED visual target for three types of eye movements: saccades, vergences and combined eye movements. Fourteen participants (6 women, mean age: 22.6 +/-0.62 years) took part in the study. Each type of eye movements was tested in two conditions: one with visual LED targets alone, the other with a sound coming for a buzzer adjacent to the LED, and preceding by 50 ms the onset of the LED target (auditory-visual target). Eye movements were recorded at 220 Hz for each eye with the Eyeseecam binocular devicehttps:// www.eyeseetec.de/eyeseecam-sci/). The results confirm that the sound significantly reduces the latency of the saccades. In contrast, for convergence or divergence the sound did not decrease the latency but it did increase the velocity and reduced the duration of such movements significantly. For combined saccade vergence movements particularly leftward, the sound had multiple effects on the saccade component: it decreased the duration of the saccade component and reciprocally increased its velocity but also reduced its latency. Such mixed effects on latency duration and velocity of the saccade component favor the hypothesis that saccade components of combined eye movements are subtended by a co-activation of both, saccade and vergence brainstem generators. The differential benefit from the sound according to the type of eye movements is of theoretical and clinical interest.