Many studies argue that synchronized movement increases prosocial attitudes and behavior. We reviewed meta-analytic evidence that reported effects of synchrony may be driven by experimenter expectancy, leading to experimenter bias; and participant expectancy, otherwise known as placebo effects. We found that a majority of published studies do not adequately control for experimenter bias and that multiple independent replication attempts with added controls have failed to find the original effects. In a preregistered experiment, we measured participant expectancy directly, asking whether participants have a priori expectations about synchrony and prosociality that match the findings in published literature. Expectations about the effects of synchrony on prosocial attitudes directly mirrored previous experimental findings (including both positive and null effects)-despite the participants not actually engaging in synchrony. On the basis of this evidence, we propose an alternative account of the reported bottom-up effects of synchrony on prosociality: the effects of synchrony on prosociality may be explicable as the result of top-down expectations invoked by placebo and experimenter effects.

Music is a human universal characterized by acoustical forms that are predictive of its behavioral functions. For example,listeners accurately distinguish between unfamiliar lullabies and other songs on the basis of their features alone. Thiscould be attributable to adults extensive musical experience, however. Here we show that infants (N = 144) relax inresponse to foreign lullabies, relative to matched foreign non-lullabies, as measured by heart rate, electrodermal activity,and pupillometry. These results were unrelated to age, suggesting the relaxation response is not a function of infantsrich musical experiences. Infants showed no visual preferences for the animated characters producing the songs, but theyattended more to the lullabies, blinking less during the singing. Moreover, the infants parents chose lullabies as the songsthat they themselves would use to calm their fussy infant. These findings raise the possibility that links between form andfunction in music are innately specified.