Synchronization in repetitive smooth movement requires perceptible events

Accurate timing performance during auditory–motor synchronization has been well documented for finger tapping tasks. It is believed that information pertaining to an event in movement production aids in detecting and correcting for errors between movement cycle completion and the metronome tone. Tasks with minimal event-related information exhibit more variable synchronization and less rapid error correction. Recent work from our laboratory has indicated that a task purportedly lacking an event structure (circle drawing) did not exhibit accurate synchronization or error correction (Studenka & Zelaznik, in press). In the present paper we report on two experiments examining synchronization in tapping and circle drawing tasks. In Experiment 1, error correction processes of an event-timed tapping timing task and an emergently timed circle drawing timing task were examined. Rapid and complete error correction was seen for the tapping, but not for the circle drawing task. In Experiment 2, a perceptual event was added to delineate a cycle in circle drawing, and the perceptual event of table contact was removed from the tapping task. The inclusion of an event produced a marked improvement in synchronization error correction for circle drawing, and the removal of tactile feedback (taking away an event) slightly reduced the error correction response of tapping. Furthermore, the task kinematics of circle drawing remained smooth providing evidence that event structure can be kinematic or perceptual in nature. Thus, synchronization and error correction, characteristic of event timing (Ivry, Spencer, Zelaznik, & Diedrichsen, 2002; Repp, 2005), depends upon the presence of a distinguishable source of sensory information at the timing goal.     

Circle drawing does not exhibit auditory-motor synchronization

Differences in timing control processes between tapping and circle drawing have been extensively documented during continuation timing. Differences between event and emergent control processes have also been documented for synchronization timing using emergent tasks that have minimal event-related information. However, it is not known whether the original circle-drawing task also behaves differently than tapping during synchronization. In this experiment, 10 participants performed a table-tapping and a continuous circle-drawing task to an auditory metronome. Synchronization performance was assessed via the value and variability of asynchronies. Synchronization was substantially more difficult in circle drawing than in tapping. Participants drawing timed circles exhibited drift in synchronization error and did not maintain a consistent phase relationship with the metronome. An analysis of temporal anchoring revealed that timing to the timing target was not more accurate than timing to other locations on the circle trajectory. The authors conclude that participants were not able to synchronize movement with metronome tones in the circle-drawing task despite other findings that cyclical tasks do exhibit auditory motor synchronization, because the circle-drawing task is unique and absent of event and cycle position information.     

Temporal Regularity of Tapping by the Left and Right Hands in Timed and Untimed Finger Tapping

The temporal characteristics of repetitive finger tapping by the left and right hands were examined in two experiments. In the first experiment, interresponse intervals (IRIs) were recorded while right-handed male subjects tapped in synchrony with an auditory timing pulse (the synchronization phase) and then attempted to maintain the same tapping rate without the timing pulses (the continuation phase). The left and right hands performed separately, at four different rates (interpulse intervals of 250, 500, 750, and 1500 ms). There was no asymmetry of the asynchronies of the timing pulses and the associated responses in the synchronization phase or of the IRIs in either phase, but there was an asymmetry in the temporal dispersion of the responses in both phases. In the second experiment, right-handed males tapped separately with each hand at three different speeds: as quickly as possible, at a fast but steady rate, and at a slow rhythmical rate. The speed asymmetry present when tapping as quickly as possible (with the preferred hand tapping more quickly) was reduced when tapping at the fast steady rate and was absent when tapping at the slow rhythmical rate. The temporal dispersion of the IRIs produced by the nonpreferred hand was greater than the temporal dispersion of those produced by the preferred hand in all speed conditions. These results show smaller temporal dispersion of tapping by the preferred hand in right-handed males under different conditions, including submaximal speeds at which both hands respond at the same rate. This suggests that the motor system controlling the preferred hand in right-handers has more precise timing of response output than that controlling the nonpreferred hand.     

Temporal regularity of tapping by the left and right hands in timed and untimed finger tapping

The temporal characteristics of repetitive finger tapping by the left and right hands were examined in two experiments. In the first experiment, interresponse intervals (IRIs) were recorded while right-handed male subjects tapped in synchrony with an auditory timing pulse (the synchronization phase) and then attempted to maintain the same tapping rate without the timing pulses (the continuation phase). The left and right hands performed separately, at four different rates (interpulse intervals of 250, 500, 750, and 1500 ms). There was no asymmetry of the asynchronies of the timing pulses and the associated responses in the synchronization phase or of the IRIs in either phase, but there was an asymmetry of chronization phase or of the IRIs in either phase, but there was an asymmetry in the temporal dispersion of the responses in both phases. in the second experiment, right-handed males tapped separately with each hand at three different speeds: as quickly as possible, at a fast but steady rate, and at a slow rhythmical rate. The speed asymmetry present when tapping as quickly as possible (with the preferred hand tapping more quickly ) was reduced when tapping at the fast steady rate and was absent when tapping at the slow rhythmical rate. The temporal dispersion of the IRIs produced by the nonpreferred hand was greater than the temporal dispersion of those produced by the preferred hand in all speed conditions. These results show smaller temporal dispersion of tapping by the preferred hand in right-handed males under different conditions, including submaximal speeds at which both hands respond at the same rate. This suggests that the motor system controlling the preferred hand in right-handers had more precise timing of response output than that controlling the nonpreferred hand.     

Développement de la précision temporo-motrice et cadences spontanées de jeunes enfants

Fifty children (six to ten years old) were asked to tap a flat surface as regularly as possible with their finger at different semi-spontaneous tempi. Their chosen tapping speed was estimated by each sequence's mean inter-tap interval. The range of chosen speeds widens with age. The just tenable difference (JTD) between inter-tap intervals is proportional to their reference, the mean. The motor-timing precision, estimated through the standard-deviation/mean ratio, clearly improves with age. Children are more precise at faster tempi, not around their “normal” tempo as adults. Our simple semi-spontaneous finger-tapping task could be applied to the clinical evaluation of age-dependent explicit and implicit timing components in motor performance.     

Perfect phase correction in synchronization with slow auditory sequences

Phase correction during synchronization (finger tapping) with an isochronous auditory sequence is typically imperfect, requiring several taps to complete. However, two independent hypotheses predict that phase correction should approach perfection when the sequence tempo is slow. The present results confirm this prediction. The experiment used a phase perturbation method and a group of musically trained participants. As the sequence interonset interval increased from 300 to 1200 ms, the phase correction response to perturbations increased and approached instantaneous phase resetting between 700 and 1200 ms, depending on the individual. A possible explanation of this finding is that emergent timing of the periodic finger movement vanishes as the movement frequency decreases and thus ceases to compete with event-based timing.     

Perfect Phase Correction in Synchronization With Slow Auditory Sequences

Phase correction during synchronization (finger tapping) with an isochronous auditory sequence is typically imperfect, requiring several taps to complete. However, two independent hypotheses predict that phase correction should approach perfection when the sequence tempo is slow. The present results confirm this prediction. The experiment used a phase perturbation method and a group of musically trained participants. As the sequence interonset interval increased from 300 to 1200 ms, the phase correction response to perturbations increased and approached instantaneous phase resetting between 700 and 1200 ms, depending on the individual. A possible explanation of this finding is that emergent timing of the periodic finger movement vanishes as the movement frequency decreases and thus ceases to compete with event-based timing.     

Phase Correction Following a Perturbation in Sensorimotor Synchronization Depends on Sensory Information

In models of sensorimotor synchronization, it is generally assumed that phase correction occurs in response to information about sensorimotor asynchrony or relative phase. Without such feedback, a phase perturbation in the motor activity should not be followed by phase correction. Alternatively, internally generated temporal expectations could provide a basis for phase correction in the absence of feedback. To test those hypotheses, the author conducted an experiment in which participants (N = 8) tapped their finger in synchrony with isochronous auditory sequences containing a single shifted event onset, after which there could be a gap of up to 3 missing events. Participants were instructed to not react to the shifted event and to continue tapping regularly during any gap. The shifted event caused an involuntary phase shift of the following tap. The shift was corrected if the sequence continued, but during a gap, the shift persisted without correction. Those results confirm that sensory feedback is necessary for phase correction to occur.     

Timing precision in continuation and synchronization tapping

 Wing and Kristofferson (1973) have shown that temporal precision in self-paced tapping is limited by variability in a central timekeeper and by variability arising in the peripheral motor system. Here we test an extension of the Wing–Kristofferson model to synchronization with periodic external events that was proposed by Vorberg and Wing (1994). In addition to the timekeeper and motor components, a linear phase correction mechanism is assumed which is triggered by the last or the last two synchronization errors. The model is tested in an experiment that contrasts synchronized and self-paced trapping, with response periods ranging from 200–640 ms. The variances of timekeeper and motor delays and the error correction parameters were estimated from the auto-covariance functions of the inter-response intervals in continuation and the asynchronies in synchronization. Plausible estimates for all parameters were obtained when equal motor variance was assumed for synchronization and continuation. Timekeeper variance increased with metronome period, but more steeply during continuation than during synchronization, suggesting that internal timekeeping processes are stabilized by periodic external signals. First-order error correction became more important as the metronome period increased, whereas the contribution of second-order error correction decreased. It is concluded that the extended two-level model accounts well for both synchronization and continuation performance. Received: 16 November 1998 / Accepted: 21 April 1999     

Linear Phase-Correction in Synchronization: Predictions, Parameter Estimation, and Simulations

A stochastic model for synchronization with a metronome is analyzed which generalizes Wing and Kristofferson's (1973a, 1973b) two-level model for tapping. The model includes a motor component, a timekeeper component, and a linear phase error correction mechanism. The model's predictions of the asymptotic dependence structure of the synchronization errors and interresponse intervals are derived. Problems of identifiability and estimation of parameters are discussed.     

Development of sensorimotor synchronization abilities: Motor and cognitive components

The aim of the present study was to examine both the development of sensorimotor synchronization in children in the age range from 5 to 8 years and the involvement of motor and cognitive capacities. Children performed a spontaneous motor tempo task and a synchronization–continuation task using an external auditory stimulus presented at three different inter-stimulus intervals: 500, 700, and 900 ms. Their motor and cognitive abilities (short-term memory, working memory, and attention) were also assessed with various neuropsychological tests. The results showed some developmental changes in synchronization capacities, with the regularity of tapping and the ability to slow down the tapping rate improving with age. The age-related differences in tapping were nevertheless greater in the continuation phase than in the synchronization phase. In addition, the development of motor capacities explained the age-related changes in performance for the synchronization phase and the continuation phase, although working memory capacities were also involved in the interindividual differences in performance in the continuation phase. The continuation phase is thus more cognitively demanding than the synchronization phase. Consequently, the improvement in sensorimotor synchronization during childhood is related to motor development in the case of synchronization but also to cognitive development with regard to the reproduction and maintenance of the rhythm in memory.     

Sensorimotor synchronization with adaptively timed sequences

Most studies of human sensorimotor synchronization require participants to coordinate actions with computer-controlled event sequences that are unresponsive to their behavior. In the present research, the computer was programmed to carry out phase and/or period correction in response to asynchronies between taps and tones, and thereby to modulate adaptively the timing of the auditory sequence that human participants were synchronizing with, as a human partner might do. In five experiments the computer's error correction parameters were varied over a wide range, including "uncooperative" settings that a human synchronization partner could not (or would not normally) adopt. Musically trained participants were able to maintain synchrony in all these situations, but their behavior varied systematically as a function of the computer's parameter settings. Computer simulations were conducted to infer the human participants' error correction parameters from statistical properties of their behavior (means, standard deviations, auto- and cross-correlations). The results suggest that participants maintained a fixed gain of phase correction as long as the computer was cooperative, but changed their error correction strategies adaptively when faced with an uncooperative computer.     

Simultaneous Event-Based and Emergent Timing: Synchronization,Continuation, and Phase Correction

It has been claimed that rhythmic tapping and circle drawing represent fundamentally different timing processes (event-based and emergent, respectively) and also that circle drawing is difficult to synchronize with a metronome and exhibits little phase correction. In the present study, musically trained participants tapped with their left hands, drew circles with their right (dominant) hands, and also performed both tasks simultaneously. In Experiment 1, they synchronized with a metronome and then continued on their own, whereas in Experiment 2, they synchronized with a metronome containing phase perturbations. Circle drawing generally exhibited reliable synchronization, although with greater variability than tapping, and also showed a clear phase-correction response that evolved gradually during the cycle immediately following a perturbation. When carried out simultaneously in synchrony, with or without a metronome, the two tasks affected each other in some ways but retained their distinctive timing characteristics. This shows that event-based and emergent timing can coexist in a dual-task situation. Furthermore, the authors argue that the two timing modes usually coexist in each individual task, although one mode is often dominant.     

Categorical time production: evidence for discrete timing in motor control.

Subjects performed a repetitive manual tapping task, attempting to match a given rate of auditory stimulus pulses, first with the pulses audible (synchronization) and then with the pulses turned off (continuation). In different sessions, the interstimulus interval (ISI) was selected from the range 175 to 825 msec in steps of 25 msec, with different ISI values presented in a random order. Across this range of ISI conditions, interresponse intervals (IRIs) exhibited alternating positive bias (too slow) and negative bias (too fast). We interpret this pattern of bias in terms of a discrete, or categorical, timing mechanism in motor timing. Categorical time production can be viewed as extending our conception of the timekeeper in Wing's (Wing & Kristofferson, 1973a, 1973b) two-process model of motor timing and may be related to the system of multiple clocks proposed by Kristofferson (1980) to explain a categorical pattern of variability measures in duration discrimination.     

Phase correction, phase resetting, and phase shifts after subliminal timing perturbations in sensorimotor synchronization.

Recent studies of synchronized finger tapping have shown that perceptually subliminal phase shifts in an auditory sequence are rapidly compensated for in the motor activity (B. H. Repp, 2000a). Experiment 1 used a continuation-tapping task to confirm that this compensation is indeed a phase correction, not an adjustment of the central timekeeper period. Experiments 2-5 revealed that this phase correction occurs even when there is no ordinary sensorimotor asynchrony--when the finger taps are in antiphase or arbitrary phase relative to the auditory sequence (Experiments 2 and 3) or when the tap coinciding with the sequence phase shift is withheld (Experiments 4 and 5). The phase correction observed in the latter conditions was instantaneous, which suggests that phase resetting occurs when the motor activity is discontinuous. A prolonged phase shift suggestive of overcompensation was observed in some conditions, which poses a challenge to pure phase correction models.     

Categorical time production: Evidence for discrete timing in motor control

Subjects performed a repetitive manual tapping task, attempting to match a given rate of auditory stimulus pulses, first with the pulses audible (synchronization) and then with the pulses turned off (continuation). In different sessions, the interstimulus interval (ISI) was selected from the range 175 to 825 msec in steps of 25 msec, with different ISI values presented in a random order. Across this range of ISI conditions, interresponse intervals (IRIs) exhibited alternating positive bias (too slow) and negative bias (too fast). We interpret this pattern of bias in terms of a discrete, or categorical, timing mechanism in motor timing. Categorical time production can be viewed as extending our conception of the timekeeper in Wing’s (Wing’ & Kristofferson, 1973a, 1973b) two-process model of motor timing and may be related to the system of multiple clocks proposed by Kristofferson (1980) to explain a categorical pattern of variability measures in duration discrimination.     

Quantifying phase correction in sensorimotor synchronization: empirical comparison of three paradigms

Tapping in synchrony with a metronome requires phase error correction, a process often described by a single-parameter autoregressive model. The parameter (α) is a measure of sensorimotor coupling strength. This study compares α estimates obtained from three experimental paradigms: synchronization with (1) a perfectly regular metronome (RM), (2) a perturbed metronome containing phase shifts (PS), and (3) an "adaptively timed" metronome (AT). Musically trained participants performed in each paradigm at four tempi, with baseline interval durations ranging from 400 to 1300 ms. Two estimation methods were applied to each data set. Results showed that all α estimates increased with interval duration. However, the PS paradigm yielded much larger α values than did the AT paradigm, with those from the RM paradigm falling in between. Positional analysis of the PS data revealed that α increased immediately following a phase shift and then decreased sharply. Unexpectedly, all PS α estimates were uncorrelated with the RM and AT estimates, which were strongly correlated. These results suggest that abruptly perturbed sequences engage a different mechanism of phase correction than do regular or continuously modulated sequences.     

Perception–production relationships and phase correction in synchronization with two-interval rhythms

Two experiments investigated the effects of interval duration ratio on perception of local timing perturbations, accuracy of rhythm production, and phase correction in musicians listening to or tapping in synchrony with cyclically repeated auditory two-interval rhythms. Ratios ranged from simple (1:2) to complex (7:11, 5:13), and from small (5:13 = 0.38) to large (6:7 = 0.86). Rhythm production and perception exhibited similar ratio-dependent biases: rhythms with small ratios were produced with increased ratios, and timing perturbations in these rhythms tended to be harder to detect when they locally increased the ratio than when they reduced it. The opposite held for rhythms with large ratios. This demonstrates a close relation between rhythm perception and production. Unexpectedly, however, the neutral “attractor” was not the simplest ratio (1:2 = 0.50) but a complex ratio near 4:7 (= 0.57). Phase correction in response to perturbations was generally rapid and did not show the ratio-dependent biases observed in rhythm perception and production. Thus, phase correction operates efficiently and autonomously even in synchronization with rhythms exhibiting complex interval ratios.     

The beneficial effect of synchronized action on motor and perceptual timing in children

We examined the role of action in motor and perceptual timing across development. Adults and children aged 5 or 8 years old learned the duration of a rhythmic interval with or without concurrent action. We compared the effects of sensorimotor versus visual learning on subsequent timing behaviour in three different tasks: rhythm reproduction (Experiment 1), rhythm discrimination (Experiment 2) and interval discrimination (Experiment 3). Sensorimotor learning consisted of sensorimotor synchronization (tapping) to an isochronous visual rhythmic stimulus (ISI = 800 ms), whereas visual learning consisted of simply observing this rhythmic stimulus. Results confirmed our hypothesis that synchronized action during learning systematically benefitted subsequent timing performance, particularly for younger children. Action‐related improvements in accuracy were observed for both motor and perceptual timing in 5 years olds and for perceptual timing in the two older age groups. Benefits on perceptual timing tasks indicate that action shapes the cognitive representation of interval duration. Moreover, correlations with neuropsychological scores indicated that while timing performance in the visual learning condition depended on motor and memory capacity, sensorimotor learning facilitated an accurate representation of time independently of individual differences in motor and memory skill. Overall, our findings support the idea that action helps children to construct an independent and flexible representation of time, which leads to coupled sensorimotor coding for action and time.     

Comments on "Rapid motor adaptations to subliminal frequency shifts during syncopated rhythmic sensorimotor synchronization" by Michael H. Thaut and Gary P. Kenyon (Human Movement Science 22 [2003] 321-338)

Thaut and Kenyon [Human Movement Sci. 22 (2003) 321] have shown that, in a task requiring tapping in antiphase with a metronome, the response period adapts rapidly to a small (+/-2%) change in the stimulus period, whereas the relative phase between stimulus and response returns to its pre-change value only very gradually. On the basis of these and earlier findings, Thaut and Kenyon argue that period adaptation is rapid and subconscious, whereas phase adaptation is slow and dependent on awareness of a phase error. This interpretation is at variance with results in the literature suggesting that phase correction is rapid and subconscious, whereas period correction is slow and dependent on awareness of a period mismatch. Although differences in terminology (adaptation versus correction) play a role in this conflict, it primarily reflects different conceptions of sensorimotor synchronization and different interpretations of empirical findings. By excluding from their model a central timekeeper or oscillator with a flexible period, Thaut and Kenyon have omitted an essential component of human timing control that is needed for a proper explanation of their results.