Does beat perception rely on the covert use of the motor system?

Does beat perception rely on the covert use of the motor system? Esther J. Walker (e1walker@cogsci.ucsd.edu) John R. Iversen (jiversen@ucsd.edu) Department of Cognitive Science, University of California, San Diego, 9500 Gilman Dr La Jolla, CA 92093-0515 USA Swartz Center for Computational Neuroscience, University of California, San Diego, 9500 Gilman Dr La Jolla, CA 92093-0559 USA Benjamin Stillerman (ben.stillerman@tufts.edu) Aniruddh D. Patel (a.patel@tufts.edu) Benjamin K. Bergen (bkbergen@cogsci.ucsd.edu) Department of Psychology Tufts University, 490 Boston Ave Medford, MA 02155 USA Abstract Listening to music often drives people to move along to the beat of that music. Past research has suggested that motor resources are recruited not just to produce a beat, but also to perceive a beat. The present study extends this correlational work and examines whether the motor system plays a functional role in beat perception using a dual-task behavioral paradigm. Wshile performance on a beat perception task was affected by a simultaneous motor task compared to a control task (Experiment 1), pitch perception was not affected (Experiment 2). Furthermore, this effect was mediated by whether or not participants had received formal musical trainings. The results suggest that the motor system may play a functional role in beat perception, even when people are not overtly moving in time to the beat. Keywords: beat perception; pitch perception; motor system; dual-task Introduction When listening to music, people often experience a compelling drive to move along to the beat. Moving along with music appears to be a human universal, appearing in very young children (Drake, Penel, & Bigand, 2000; Kirschner & Tomasello, 2009) and across the world’s cultures (Brown, 2003; Nettl, 2000). Thus, perhaps it’s not surprising that a variety of neuroscientific research suggests a tight link between the auditory and motor systems in rhythm processing (for a review see Zatorre, Chen, & Penhune, 2007). This body of work suggests that the motor system is activated not only during beat production, but also during beat perception, even when an overt movement is not produced. For instance, the perception and production of musical rhythm both activate brain areas implicated in motor processing, including the supplementary motor area (SMA), premotor cortex (PMC), the cerebellum, and the basal ganglia (Grahn & Brett, 2007; Grahn & Rowe, 2009; Grahn, 2009). Furthermore, based on MEG data, Iversen, Repp, and Patel (2009) have suggested that the motor system influences one’s interpretation of the metricality of a sound, even when individuals are not required to move when perceiving a beat. Behavioral research also supports this idea. For example, Phillips-Silver and Trainor found in both infants (2005) and adults (2007) that moving in time Department of Cognitive Science, University of California, San Diego, 9500 Gilman Dr La Jolla, CA 92093-0515 USA with a particular musical beat influences one’s perception of that music’s rhythm. However, although studies like these have revealed motor system activity during both production and perception of a musical beat, it is largely unknown whether or not the motor system plays a functional role in beat perception. Is activation in motor areas during beat perception simply the result of associating music with movement (that in some cases is simply not expressed muscularly)? Or does motor activation reflect calculations used to perceive a beat? For instance, perhaps individuals, upon hearing music, use motor planning areas to simulate moving to the beat. This motor activity might then allow an individual to decide whether the music is on or off beat, as put forth by the action simulation for auditory prediction (ASAP) hypothesis (Patel & Iversen, in press). The present pair of studies aims to address this issue using a dual-task behavioral paradigm. In order to investigate the functional role of the motor system in beat perception, we prevented people from moving to the beat (or even thinking about moving to the beat, and presumably from engaging motor planning areas in action simulation) by tying up their motor system with an unrelated secondary motor task. This allowed us to ask whether beat perception is selectively impaired by a simultaneous motor task. If the motor system plays a functional role in beat perception then we would expect to see worse performance on beat perception during a motor task, but no such impairment on a different perceptual task that does not rely as extensively on the motor system. Experiment 1 In Experiment 1, participants listened to clips of music and had to decide whether an overlaid beat track was on or off the beat of the music. Critically, they simultaneously performed one of two secondary tasks, a Motor task, which was designed to occupy the motor system, and a color change detection task that served as a Control. To interfere with the motor system, the Motor task had participants continuously track a pseudo-randomly moving dot on a computer screen with a computer mouse (more details can be found in the methods section). Such visually- guided motor movement is thought to involve many of the areas also implicated in beat perception, including