The benefit of gestures during communication: evidence from hearing and hearing-impaired individuals

There is no doubt that gestures are communicative and can be integrated online with speech. Little is known, however, about the nature of this process, for example, its automaticity and how our own communicative abilities and also our environment influence the integration of gesture and speech. In two Event Related Potential (ERP) experiments, the effects of gestures during speech comprehension were explored. In both experiments, participants performed a shallow task thereby avoiding explicit gesture-speech integration. In the first experiment, participants with normal hearing viewed videos in which a gesturing actress uttered sentences which were either embedded in multi-speaker babble noise or not. The sentences contained a homonym which was disambiguated by the information in a gesture, which was presented asynchronous to speech (1000 msec earlier). Downstream, the sentence contained a target word that was either related to the dominant or subordinate meaning of the homonym and was used to indicate the success of the disambiguation. Both the homonym and the target word position showed clear ERP evidence of gesture-speech integration and disambiguation only under babble noise. Thus, during noise, gestures were taken into account as an important communicative cue. In Experiment 2, the same asynchronous stimuli were presented to a group of hearing-impaired students and age-matched controls. Only the hearing-impaired individuals showed significant speech-gesture integration and successful disambiguation at the target word. The age-matched controls did not show any effect. Thus, individuals who chronically experience suboptimal communicative situations in daily life automatically take gestures into account. The data from both experiments indicate that gestures are beneficial in countering difficult communication conditions independent of whether the difficulties are due to external (babble noise) or internal (hearing impairment) factors.