Stringed instrument bowing is a complex sensorimotor skill, involving fine regulation of bow orientation and motion relative to the string. In this study, we characterize this skill in terms of stabilization of specific bow parameters as well as the underlying use and coordination of the degrees of freedom (DOF) of the right bowing arm. Age-matched samples of 10 advanced cellists and 10 cello novices took part in the study. Kinematic bow movement data were analyzed with respect to task variables suggested by the cello teaching literature: position and orientation of the bow relative to the string, bow velocity, and timing. Joint motion of the bowing arm was analyzed in terms of movement amplitude and inter-joint coordination (principal component analysis). As expected, novices showed poorer control of bowing parameters. In addition, novices differed markedly from advanced players in the use and coordination of the DOF of the bowing arm, with the elbow and wrist showing less overall movement and a reduced proportion of variance explained by the first principal component (PC1). In contrast, larger amounts of shoulder variance were explained by PC1 in novices compared to experts. Our findings support Bernstein's theory of graded skill acquisition, according to which early stages of motor skill learning are characterized by a ''freezing'' of movement DOF, while later learning stages exploit the DOF, possibly following a proximal-to-distal sequence, for improved task performance.

Theoretical and empirical evidence suggests that accurate and efficient motor performance may be achieved by task-specific exploitation of biomechanical degrees of freedom. We investigate coordination of the right arm in a task requiring a sudden yet precisely controlled reversal of movement direction: bow reversals during continuous (“legato”) tone production on a stringed instrument. Ten advanced or professional cello players (at least 10 years of practice) and ten age-matched novice players took part in the study. Kinematic data from the bow and the right arm were analyzed in terms of velocity and acceleration profiles, as well as temporal coordination along the arm. As expected, experts' bow velocity and acceleration profiles differed markedly from those of novice participants, with higher peak accelerations and quicker direction changes. Importantly, experts achieved the change in movement direction with a single acceleration peak while novices tended to use multiple smaller acceleration peaks. Experts moreover showed a proximal-distal gradient in timing and amplitudes of acceleration peaks, with earlier and lower-amplitude reversals at more proximal joints. We suggest that this coordination pattern allows generating high accelerations at the end effector while reducing the required joint torques at the proximal joints. This may underlie experts' ability to produce fast bow reversals efficiently and with high spatiotemporal accuracy. The findings are discussed in terms of motor control theory as well as potential implications for musicians' performance and health.

Based on a newly developed method that combines finger position tracking and spectral analysis of the concurrent acoustic record, we studied the accuracy and variability of pitch performance in eight skilled cellists and the role of acoustic feedback in their performance. The tasks required shifting movements between pairs of notes and separated by various distances (pitch intervals) on a single string at the rate of 1 note/s. The same tasks were performed either using the bow, providing acoustic feedback, or without the bow. Overall, our subjects exhibited a high degree of accuracy in executing tasks when using the bow. When using the bow, two types of variability were observed: (1) trial-to-trial variability: in most subjects the mean fundamental frequency of a single nominal note was significantly different from trial to trial; and (2) within-trial variability. The within-trial variability includes two sub-types: (a) the pitch of a given note changed between notes within a 50-note trial; and (b) within a single note there were positional changes that we hypothesize are attempts by the performer to adjust the fundamental pitch within the note. When acoustic feedback was absent, note distributions were shifted, multimodal, and had large variability; error-correction movements within a single note also significantly decreased, indicating that the stability and precision of the motor map depends on constant re-calibration and updating by acoustic information. Our results suggest that a performer's intonation should not be viewed as a fixed entity implied by the score but as a sample from a statistical distribution.

Accuracy of shifting movements between two notes was examined in nine cellists (intermediate-professional skill levels). Three pairs of notes separated by different distances were tested under the same movement rate. Finger position on the string was measured by a circuit. Angular velocities of the left upper arm and forearm were measured by two angular velocity sensors; thus elbow angular velocity during shifts was estimated. Results showed that with increased elbow velocity and shifting distance endpoint variability stayed constant. The force of gravity assisted elbow extension during shifts toward higher pitched notes compared to flexion towards lower pitched notes, but faster movement velocity did not result in increased landing variability. Performance for note E on the A string was found to be less variable than other notes, suggesting that physical cue from the cello body geometry was used as a landmark for finger position. Cutaneous feedback from the thumb when hitting the body-neck junction enabled faster elbow extension velocity compared to shifts towards other notes. Cellists who showed higher performance accuracy also showed higher perceptual ability and performance proficiency. These results suggest that long-term over-training of fast and accurate movements enables musicians to maintain accuracy and variability across different movement distances and velocities. Higher perceptual ability and performance proficiency are correlated with increased accuracy but not lower variability, indicating although perceptual ability and performance proficiency are important for pitch accuracy, movement variability is still constrained by the capacity of the motor system, which is highly fine-tuned and different than non-musicians.