Perceptual and Cognitive Enhancement With an Adaptive Timing Partner: Electrophysiological Responses to Pitch Change Takayuki Nakata and Laurel J. Trainor Future University Hakodate and McMaster University When 2 people tap together, they adjust their timing to their partner. We investigated whether having an adaptive partner leads to better pitch perception and cognition (measured by electrophysiological mismatch negativity [MMN] and N400 responses to pitch change) compared with having a nonadaptive partner. In the nonadaptive condition, people tapped along to 3 tones generated by the computer at a fixed 800 ms interonset interval (IOI). In the adaptive condition, the computer continuously adjusted the IOI of the tones in response to the taps of the subject. Twenty percent of the time, the fourth tone was changed in pitch by 1/48th octave. Results showed that both MMN and N400 were enhanced in response to deviant targets with the adaptive compared to nonadaptive partner, suggesting that having an adaptive partner enables better perception and cognitive processing of the contents of a sound sequence. Keywords: entrainment, timing, ERP, MMN, N400 When two people play music together, they need to control the timing of their own actions while also adjusting their actions in response to those of the other (Nowicki, Prinz, Grosjean, Repp, & Keller, 2013; Wing, Endo, Bradbury, & Vorberg, 2014). Having a partner who adapts can be satisfying. Patients playing a percussion instrument with a music therapist who entrains to them may gain a sense of freedom in expressing their emotion and feel empow- ered by the experience (Bensimon, Amir, & Wolf, 2008; Winkel- man, 2003). In many species, individuals synchronize their movements to- gether, such as birds that fly in formation, fish that swim in schools, and fireflies that flash at the same time (Buck, 1935, 1937, 1988; Partridge, 1982; Weimerskirch, Martin, Clerquin, Alexan- dre, & Jiraskova, 2001). More rare, but found in humans and a few vocal learning species, is the ability to synchronize movement to a predictable auditory stimulus, such as the beat in music (Patel & Iversen, 2014; Patel, Iversen, Bregman, & Schulz, 2009; Schach- ner, Brady, Pepperberg, & Hauser, 2009; Trainor, 2015). This ability is referred to as sensorimotor synchronization (SMS) and is defined as “the coordination of rhythmic movement with an ex- ternal rhythm” (Repp & Su, 2013). In a typical musical performance, the underlying beat or tempo produced is not completely steady, with deviations arising from several sources, such as internal time-keeping errors (Torre & Delignières, 2008; Wing & Kristofferson, 1973a, 1973b), and deliberate deviations for expressive purposes (James, Michel, Britz, Vuilleumier, & Hauert, 2012; Rankin, Large, & Fink, 2009; Repp, 1992). Thus, for two or more people to play music together in synchrony, it necessarily involves mutual adjustments of phase alignment and tempo (period) to achieve SMS. The study of interpersonal synchrony is particularly important because empirical evidence indicates that synchronous movement promotes a sense of group affiliation. For example, walking or singing in synchrony with others increases cooperation, trust, and ratings of likability among participants (Hove & Risen, 2009; Kirschner & Tomasello, 2010; Valdesolo, Ouyang, & DeSteno, 2010; Wiltermuth & Heath, 2009). Synchronous movement to music even leads to enhanced prosocial instrumental helping in infants (Cirelli, Einarson, & Trainor, 2014; Cirelli & Trainor, 2015). Cirelli, Wan, and Trainor (2014) bounced 14-month-old infants to music facing an experimenter who bounced in synchrony with the infant, or in antiphase (but at the same tempo), or at a different tempo from the infant. After this experience, infants were more likely to help the experimenter by retrieving “accidentally” dropped items needed to complete a task if they had bounced at the same tempo as the experimenter (either in phase or antiphase) compared with if they bounced at a different tempo, whether faster or slower. Of interest to the authors, this increase in helping after synchronous bouncing is targeted to the bouncing partner and not to neutral strangers (Cirelli, Wan, et al., 2014), although it does apply to friends of the synchronous bouncing partner (Cirelli & Trainor, 2015). It has been proposed that three core cognitive-motor skills are needed for people to engage in real-time interpersonal coordina- tion—(a) propensity to synchronize movements, (b) ability to use anticipatory mechanisms during SMS, and (c) ability to divide attention (reviewed by Keller, Novembre, & Hove, 2014), re- viewed in more detail below. In the present study, we investigate perceptual/cognitive consequences of playing with an adaptive partner. In particular, during a difficult SMS task, we expect that TAKAYUKI NAKATA is a Professor of Psychology in the Department of Complex and Intelligent Systems at Future University Hakodate. LAUREL J. TRAINOR is a Professor of Psychology in the Department of Psychology, Neuroscience and Behaviour and the Director of the Mc- Master Institute for Music and the Mind (MIMM) at McMaster University. Funded by grants from the Japan Society for the Promotion of Science to Takayuki Nakata. Correspondence concerning this article should be addressed to Takayuki Nakata, Department of Complex and Intelligent Systems, Future Univer- sity Hakodate, Hakodate, Hokkaido, Japan 041-8655. E-mail: nakata@fun .ac.jp This document is copyrighted by the American Psychological Association or one of its allied publishers. This article is intended solely for the personal use of the individual user and is not to be disseminated broadly. Psychomusicology: Music, Mind, and Brain © 2015 American Psychological Association 2015, Vol. 25, No. 4, 404 – 415 0275-3987/15/$12.00 http://dx.doi.org/10.1037/pmu0000120 404