**Down-regulation of left posterior parietal cortex impairs musical phase shift detection in subjects with good perceptual acuity for phase timing**
Jessica M. Ross (1), Shannon Proksch (2), John R. Iversen (3), Ramesh Balasubramaniam (2)
(1) Berenson-Allen Center for Noninvasive Brain Stimulation, Harvard Medical School, Boston,
(2) Cognitive & Information Sciences, Univ. of California, Merced,
(3) Swartz Center for Computational Neuroscience, Univ. of California, San Diego
Previous work with transcranial magnetic stimulation (TMS) demonstrated a causal relationship between dorsal auditory stream function and musical beat perception. Specifically, cTBS to a left posterior parietal (PPC) target, applied to disrupt dorsal stream network activity, interfered with accurate detection of shifts of beat-phase, but did not interfere with absolute interval timing discrimination or detection of changes in musical tempo. This is preliminary data with N=33 and a target sample of N=35. We examined whether the right PPC, which is implicated in many aspects of spatial cognition and pitch transformation, is also causally involved in beat-based musical timing perception. Additionally, we examined whether there are differences between left and right hemisphere PPC involvement in beat-based timing perception. We compared the perceptual effects of downregulating the left versus right PPC in 33 participants to discover hemispheric differences in absolute and beat-based musical timing perception. Three aspects of timing perception were investigated: 1) discrete interval timing discrimination, as well as two facets of relative beat-based musical timing-detection of alterations to 2) tempo (sped up/slowed down) and 3) shifts in phase (forward/back). Participants were tested pre- and post- stimulation using a psychoacoustic test of sub-second interval discrimination and the Adaptive Beat Alignment Test (A-BAT) subtests. Preliminary data suggest a role for the left PPC in detecting shifts in phase, but not interval discrimination or tempo detection. In the current study, down-regulation of left PPC impaired accurate detection of beat-phase, but only in participants with a low baseline threshold. This is consistent with Ross et al., 2018, where the impairment effect of cTBS to left PPC in phase-shift detection was strongest in participants with a low baseline threshold. The data do not suggest a complimentary role of the right PPC in phase shift detection, perhaps indicating a left parietal dominance for beat-based timing perception. The right PPC was also not implicated in interval discrimination or tempo detection. We discuss these trends in the context of hemispheric and functional differences across the parietal lobes and the Action Simulation for Auditory Prediction (ASAP) hypothesis.
Contact:
jross4@bidmc.harvard.edu
https://jessicamarieross.com/
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