Multisensory and motor integration in stimulus detection in monkeys

Céline Cappe, Unit of Physiology - Dept. of Medicine - University of Fribourg and Centre de Recherche Cerveau et Cognition (UMR 5549) CNRS - University Paul Sabatie

Abstract
On the psychophysical point of view, multisensory integration allows a decrease of reaction time and better performance in sensori-motor tasks, as reported for human subjects engaged in auditory-visual recognition task. As few data are available in behaving monkey engaged in similar protocols, the present study investigates the interaction between auditory and visual stimuli in monkey.
Adult macaque monkeys (n=2) were trained in a visuo-auditory detection task. The monkeys had to generate a motor response in a reaction time paradigm whenever a visual, an auditory or a visuo-auditory signal was presented. Does, as in human, the synergy derive from the bimodal stimuli shorten the reaction time and improve detection when compared to unimodal conditions? At near threshold conditions of both visual and auditory stimuli, the bimodal condition has a significant facilitatory effect on reaction times and stimulus detection. Indeed, correct responses raised from 48% for unimodal conditions to 90% for bimodal conditions and the reactions times in multisensory conditions were 12% shorter on the average than unimodal conditions.
These findings confirm in monkeys the rule of the inverted effectiveness feature of multisensory integration expressed as a significant gain in stimulus detection at near threshold condition which disappeared at higher intensities.

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