<p>The universality and antiquity of music and dance suggest that they may serve some important adaptive function. Why are music and dance cultural universals? One popular theory is that music and dance function to enhance mutually benefiting cooperation. While the cooperation hypothesis finds support from anthropological observations and recent experiments, the proximate mechanisms remain unclear. In this thesis, I examine if being in synchrony is a critical factor underlying music and dance’s cooperative effects. I define synchrony as rhythmically moving or vocalising in time with others. In support of synchrony’s role in fostering cooperation, a number of studies exploring two person interactions have found positive social effects from synchrony. However, it is not clear whether synchrony enhances cooperation in groups larger than two as typical with music and dance. This thesis describes five laboratory experiments that were conducted to investigate: (1) whether group synchrony increases cooperation; and (2) which psychological mechanisms are involved in producing synchrony’s cooperative effects. In the first three experiments, small groups of participants were asked to perform body movements or to vocalise words in time with the same (synchrony condition) or different (asynchrony condition) metronome beats. Cooperative behaviour was measured with a helping scenario and an economic game. A small increase in cooperation was found with synchronous movement compared to asynchronous movement (experiment 1 and 3). However, this difference was only significant with the economic game measure (experiment 3). When vocalisation was isolated (experiment 2), contrary to expectations, the highest level of helping occurred after the asynchrony vocal condition. A plausible explanation for such small and inconsistent effects comes from the method in which synchrony was manipulated. Following previous methodologies, the goal for participants was to entrain to their own beat. Yet in natural human ecologies, synchrony is a product of shared intentionality – the sharing of psychological states to produce collaborative behaviour. To better understand the contribution of shared intentionality, experiments 4 and 5 varied synchrony with shared intentionality, and then measured cooperation. These experiments revealed that when participants worked together to create synchrony, substantial increases in cooperation were found, for both synchronous vocalisations (experiment 4) and for synchronous movements (experiment 5). Synchrony was also found to significantly amplify two key hypothesised mediating variables: perceived similarity and entitativity (the degree to which a collection of people are perceived as a group). Path analysis supported a proposed mechanism by which synchrony combines with shared intentionality to produce greater cooperation through: (1) increased attention to the behaviours of other participants; and (2) reinforcement of successful cooperation. This thesis, therefore, extends previous research on group music and dance in three ways. First, the combined effect of synchrony and shared intentionality is identified as critical to the cooperation enhancing effects of music and dance. Second, it describes plausible mechanisms for how synchrony may lead to increased cooperation. Third, it provides empirical evidence in support of these mechanisms.</p>
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