A multisensory causal inference prior is attenuated in musicians and is further attenuated following instruction

A fundamental question in psychology and neuroscience is whether expertise can generalize to improvements in basic sensory perception. Recent work suggests that musicians exhibit domain-general advantages in multisensory spatial integration, which has implications for our understanding of plasticity in sensory processing. Yet, the cause of this effect of expertise is unclear. Here, a preregistered sample of 35 musicians and 35 nonmusicians localized brief flashes and noise bursts, unimodally and bimodally, along the azimuth. Via Bayesian causal inference, we modeled participants' sensory precision and their prior tendency to perceptually integrate the stimuli (pcommon). As hypothesized, musicians exhibited less ventriloquism (audition biased toward vision) than nonmusicians, and this was captured by a reduced pcommon rather than by differences in sensory precision. Furthermore, although pcommon (and ventriloquism) was reduced after we told participants how often the stimuli were colocated, this did not eliminate the group difference in pcommon. Our results suggest that musicians have reduced susceptibility to a famous multisensory illusion, as accounted for by a Bayesian prior, and we show that such a prior (and illusory perception) can be modulated by a simple instruction.