Subdividing the Beat: Auditory and Motor Contributions to Synchronization
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Music2605_03 5/8/09 6:29 PM Page 415 Auditory and Motor Contributions to Synchronization 415 SUBDIVIDING THE BEAT: AUDITORY AND MOTOR CONTRIBUTIONS TO SYNCHRONIZATION JANEEN D. LOEHR AND CAROLINE PALMER that are subdivided by those of other performers, and McGill University, Montreal, Canada vice versa. Those subdivisions give rise to additional auditory and motor information, which could influ- THE CURRENT STUDY EXAMINED HOW AUDITORY AND ence performers’ ability to synchronize. The current kinematic information influenced pianists’ ability to study addressed the role of sensory information from synchronize musical sequences with a metronome. subdivisions in synchronized music performance. Does Pianists performed melodies in which quarter-note hearing tones or producing movements between syn- beats were subdivided by intervening eighth notes that chronized tones influence pianists’ ability to synchro- resulted from auditory information (heard tones), nize melodies with a metronome? motor production (produced tones), both, or neither. When nonmusicians tap along with an isochronous Temporal accuracy of performance was compared with auditory pacing sequence, their taps precede the pacing finger trajectories recorded with motion capture. tones by 20 to 80 ms on average (Aschersleben, 2002). Asynchronies were larger when motor or auditory sen- The tendency for taps to precede the pacing tones has sory information occurred between beats; auditory been termed the mean negative asynchrony (MNA) information yielded the largest asynchronies. Pianists and is smaller in musicians than nonmusicians were sensitive to the timing of the sensory information; (Aschersleben, 2002). The presence of additional tones information that occurred earlier relative to the mid- between tones of the pacing sequence reduces the MNA, point between metronome beats was associated with whether these tones evenly subdivide the pacing inter- larger asynchronies on the following beat. Finger vals (as in 1:n tapping, when participants tap with every motion was influenced only by motor production nth tone of the pacing sequence; Repp, 2003), are timed between beats and indicated the influence of other fin- randomly with respect to the pacing sequence gers’ motion. These findings demonstrate that synchro- (Wohlschläger & Koch, 2000), or are part of a complex nization accuracy in music performance is influenced rhythm (as in synchronizing with music; Thaut, by both the timing and modality of sensory informa- Rathbun, & Miller, 1997). The MNA also is reduced tion that occurs between beats. when participants produce movements between syn- chronized taps. In n:1 tapping, in which participants Received September 1, 2008, accepted February 18, 2009. produce n taps for every tone of the pacing sequence, Key words: synchronization, timing, finger motion, asynchronies decrease as the number of taps between music performance, auditory feedback synchronized taps increases from two to three (Pressing, 1998). Asynchronies also are reduced when participants produce non-contact movements between taps. Wohlschläger and Koch (2000) recorded finger motion OST SENSORIMOTOR SYNCHRONIZATION trajectories during synchronization tapping and found research focuses on the synchronization of that asynchronies were smaller when a local minimum Msimple movements (finger taps) with in height above the tapping surface subdivided the sequences ranging from simple (such as isochronous interval between taps. They proposed that the MNA tones) to complex (such as rhythms; see Repp, 2005, occurs because participants underestimate the duration 2006, for reviews). Relatively little is known, however, of empty intervals, and that auditory or motor subdivi- about how complex sequences such as musical sions can increase the accuracy of duration estimates by melodies are synchronized. Music ensemble perform- providing structure for those intervals. ance often requires synchrony among performers who Both auditory and motor subdivisions between tones produce different rhythms (see Goebl & Palmer, 2009). commonly occur in music ensemble performance. A Each performer must synchronize temporal intervals given interval can be subdivided by tones produced by Music Perception VOLUME 26, ISSUE 5, PP. 415–425, ISSN 0730-7829, ELECTRONIC ISSN 1533-8312 © 2009 BY THE REGENTS OF THE UNIVERSITY OF CALIFORNIA. ALL RIGHTS RESERVED. PLEASE DIRECT ALL REQUESTS FOR PERMISSION TO PHOTOCOPY OR REPRODUCE ARTICLE CONTENT THROUGH THE UNIVERSITY OF CALIFORNIA PRESS’S RIGHTS AND PERMISSIONS WEBSITE, HTTP://WWW.UCPRESSJOURNALS.COM/REPRINTINFO.ASP. DOI:10.1525/MP.2009.26.5.415 Music2605_03 5/8/09 6:29 PM Page 416 416 Janeen D. Loehr & Caroline Palmer another performer, in which case auditory information Method from the subdivision is available, or by the performer him/herself, in which case both auditory and movement- Participants related information are available. Previous findings indicate that the sensorimotor information arising One male and sixteen female pianists, ranging in age from synchronized taps influences synchronization from 17 to 27 years (M = 20.59, SD = 2.52), were accuracy. The MNA is reduced when auditory feedback recruited from the McGill community. All participants accompanies each tap in addition to the tactile and had at least 7 years of piano instruction (M = 11.06, SD = kinesthetic feedback already available (Aschersleben & 2.80), and all but one were right-handed.1 All partici- Prinz, 1995). The MNA is increased when tactile and pants gave informed consent according to the proce- kinesthetic feedback are reduced through weaker tap- dures approved by the Institutional Review Board of ping movements with smaller amplitude or force McGill University and all procedures were consistent (Aschersleben, Gehrke, & Prinz, 2004) or eliminated with the Helsinki Declaration. through anesthesia (Aschersleben, Gehrke, & Prinz, 2001). Although these findings, and the sensory Stimulus Materials and Design accumulator model proposed to explain them (Aschersleben, 2002), are concerned only with the Two sets of four two-measure melodies were designed effects of feedback accompanying synchronized taps, for the study. The first measure of one set of melodies they raise the possibility that synchronization accuracy is shown in the left panel of Figure 1. Each melody con- might also differ depending on the types of sensory tained eighth notes on all beats (1 beat = 1 quarter note information that accompany subdivisions. in all melodies). Within each set, one melody contained The current study addressed two questions. First, no subdivisions between quarter-note beats (labeled does sensorimotor information between tones in “NONE” in the figure and referred to as the no-subdi- musical sequences influence pianists’ ability to syn- vision melody in text); the others contained eighth chronize their performances with a metronome? notes subdividing odd beats (ODD), even beats Second, do these effects differ depending on whether the (EVEN), or all beats (ALL). All melodies were written information is auditory, motor (movement-generated), in 4/4 meter and were performed with the right hand. or both? Experienced pianists performed melodies One set of melodies was notated in the key of C major with a metronome. The task was manipulated so that and the other in G major. Only the first five notes of auditory information, motor production, both, or nei- each scale were used so that participants did not have to ther occurred between synchronized tones. We reposition their hands during performance. Beats were hypothesized that both auditory information and produced approximately equally often by each of the motor production between tones would reduce the fingers and thumb. MNA, consistent with the tapping literature and the Participants produced each notated melody while duration underestimation hypothesis proposed by hearing one of the four melodies within each set, in a Wohlschläger and Koch (2000). We also hypothesized within-subjects design. This design is depicted schemat- that the combined auditory and motor information ically in Figure 1. Produced melodies appear on the left would reduce asynchronies more than either alone, side of the figure and the associated auditory feedback given previous reports that providing auditory feed- on the right side. Participants completed the fully back in addition to motion-generated feedback on crossed design, which yielded 16 combinations of pro- synchronized taps reduces the MNA. Wohlschläger and duced and heard melodies. Lines connecting the Koch (2000) attributed the reduced asynchrony when melodies in Figure 1 denote the 10 conditions in which all non-contact movements occurred between taps to subdivisions resulted from motor production only, audi- changes in finger motion trajectories. It is possible that tory information only, both, or neither (analyzed sepa- similar changes in motion trajectories might underlie rately, below). In all cases where produced and heard increased synchronization accuracy when participants notes coincided (for example, all quarter-note beats), par- hear but do not have to produce subdivisions, particu- ticipants heard the auditory feedback associated with the larly given the close link between auditory and motor keystroke they produced. In the control condition, networks in musicians (e.g., Haueisen & Knösche, 2001). We therefore recorded and analyzed pianists’ finger motions, and hypothesized that subdivision 1The pattern of results did not change when the left-handed