Phase attraction in sensorimotor synchronization with auditory sequences: effects of single and periodic distractors on synchronization accuracy

Four experiments showed that both single and periodic distractor tones affected the timing of finger taps produced in synchrony with an isochronous auditory target sequence. Single distractors had only small effects, but periodic distractors occurring at various fixed or changing phase relationships exerted strong phase attraction. The attraction was asymmetric, being stronger when distractors preceded target tones than when they lagged behind. A large pitch difference between target and distractor tones (20 vs. 3 semitones) did not reduce phase attraction substantially, although in the case of continuously changing phase relationships it did prevent complete capture of the taps by the distractors. The results support the hypothesis that phase attraction is an automatic process that is sensitive primarily to event onsets.     

Multiple temporal references in sensorimotor synchronization with metrical auditory sequences

A local phase perturbation in an auditory sequence during synchronized finger tapping elicits an automatic phase correction response (PCR). The stimulus for the PCR is usually considered to be the most recent tap-tone asynchrony. In this study, participants tapped on target tones ("beats") of isochronous tone sequences consisting of beats and subdivisions (1:n tapping). A phase perturbation was introduced either on a beat or on a subdivision. Both types of perturbation elicited a PCR, even though there was no asynchrony associated with a subdivision. Moreover, the PCR to a perturbed beat was smaller when an unperturbed subdivision followed than when there was no subdivision. The relative size of the PCRs to perturbed beats and subdivisions depended on tempo, on whether the subdivision was local or present throughout the sequence, and on whether or not participants engaged in mental subdivision, but not on whether or not taps were made on the subdivision level. The results show that phase correction in synchronization depends not merely on asynchronies but on perceptual monitoring of multiple temporal references within a metrical hierarchy.     

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.     

Rate limits in sensorimotor synchronization with auditory and visual sequences: the synchronization threshold and the benefits and costs of interval subdivision

Synchronization of finger taps with an isochronous event sequence becomes difficult when the event rate exceeds a certain limit. In Experiment 1, the synchronization threshold was reached at interonset intervals (IOIs) above 100 ms with auditory tone sequences (in a 1:4 tapping task) but at IOIs above 400 ms with visual flash sequences (1:1 tapping). Using IOIs above those limits, the author investigated in Experiment 2 the reduction in the variability of asynchronies that tends to occur when the intervals between target events are subdivided by additional identical events (1:1 vs. 1:n tapping). The subdivision benefit was found to decrease with IOI duration and to turn into a cost at IOIs of 200-250 ms in auditory sequences and at IOIs of 450-500 ms in visual sequences. The auditory results are relevant to the limits of metrical subdivision and beat rate in music. The visual results demonstrate the remarkably weak rhythmicity of (nonmoving) visual stimuli.     

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.     

Atypical non-verbal sensorimotor synchronization in adults who stutter may be modulated by auditory feedback

PurposeTo investigate if non-verbal sensorimotor synchronization abilities in adult individuals who stutter (IWS) differ from non-stuttering controls (NS) under various performance conditions (tempo, auditory feedback, use of hands [single/both] and rhythm).MethodsParticipants were 11 IWS (5 males, 6 females, Mean age = 25.8, SD = 8.7) and 11 age- and gender-matched controls (Mean age = 24.4, SD = 8.4). During the experiment, participants were asked to prepare three melodies and subsequently perform them with a metronome at different rates and auditory feedback modalities (non-altered and suppressed). For each task/condition we tracked timing asynchrony related to the steady metronome beat.Results and conclusionsOverall, IWS displayed significantly higher timing asynchrony. Of all conditions, auditory-feedback distinguished IWS from NS most strongly, a subgroup of IWS significantly benefitting from the absence of auditory feedback. In addition, IWS showed a non-significant trend of higher negative mean asynchrony (NMA) and were more affected by the slower rate and increased rhythmic complexity and occasionally suggested poorer beat perception. These results suggest aberrant timing of sensorimotor network interaction associated with the origin of developmental stuttering.     

Automaticity and voluntary control of phase correction following event onset shifts in sensorimotor synchronization

Seven experiments show that an event onset shift (EOS) in an auditory sequence causes an involuntary phase correction response (PCR) in synchronized finger tapping. This PCR is (a) equally large in inphase and antiphase tapping; (b) reduced but still present when the EOS occurs in either of two interleaved (target-distractor) sequences; (c) unaffected by increased pitch separation between these sequences; (d) asymptotic in magnitude as EOS magnitude increases, unlike the intentional PCR to expected phase shifts; and (e) enhanced when the EOS precedes the onset of tapping, because of phase resetting. Thus, phase correction is revealed to be partially automatic and partially under voluntary control, and to be based mainly on temporal information derived from simple onset detection.     

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.     

Auditory dominance in temporal processing: new evidence from synchronization with simultaneous visual and auditory sequences

Evidence that audition dominates vision in temporal processing has come from perceptual judgment tasks. This study shows that this auditory dominance extends to the largely subconscious processes involved in sensorimotor coordination. Participants tapped their finger in synchrony with auditory and visual sequences containing an event onset shift (EOS), expected to elicit an involuntary phase correction response (PCR), and also tried to detect the EOS. Sequences were presented in unimodal and bimodal conditions, including one in which auditory and visual EOSs of opposite sign coincided. Unimodal results showed greater variability of taps, smaller PCRs, and poorer EOS detection in vision than in audition. In bimodal conditions, variability of taps was similar to that for unimodal auditory sequences, and PCRs depended more on auditory than on visual information, even though attention was always focused on the visual sequences.     

Temporal control of movements in sensorimotor synchronization.

Under conditions in which the temporal structure of events (e.g., a sequence of tones) is predictable, performing movements in synchrony with this sequence of events (e.g., dancing) is an easy task. A rather simplified version of this task is studied in the sensorimotor synchronization paradigm. Participants are instructed to synchronize their finger taps with an isochronous sequence of signals (e.g., clicks). Although this is an easy task, a systematic error is observed: Taps usually precede clicks by several tens of milliseconds. Different models have been proposed to account for this effect ("negative asynchrony" or "synchronization error"). One group of explanations is based on the idea that synchrony is established at the level of central representations (and not at the level of external events), and that the timing of an action is determined by the (anticipated) action effect. These assumptions are tested by manipulating the amount of sensory feedback available from the tap as well as its temporal characteristics. This article presents an overview of these representational models and the empirical evidence supporting them. It also discusses other accounts briefly in the light of further evidence.     

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.     

Processes underlying adaptation to tempo changes in sensorimotor synchronization

In synchronizing finger taps with an auditory sequence, a small sudden tempo ("step") change in the sequence tends to be followed by rapid adaptation of the tapping period but slow adaptation of the relative phase of the taps, whereas a larger step change leads to initial period overshoot followed by rapid adaptation of both period and phase [M.H. Thaut, R.A. Miller, L.M. Schauer, Biological Cybernetics 79 (1998a) 241-250]. Experiment 1 replicated these findings and showed that the transition between the two patterns of adaptation occurs near the perceptual detection threshold for a tempo change. A reasonable explanation of these data was provided by a dual-process model of internal error correction [J. Mates, Biological Cybernetics 70 (1994a) 463-473, 70 (1994b) 475-484], with the added assumption that one process (period correction) depends on conscious awareness of a tempo change whereas the other (phase correction) does not. This assumption received support in Experiment 2, where a synchronization-continuation tapping task was used in combination with perceptual judgments to probe into the process of period correction following step changes. The results led to the conclusion that rapid adaptation of the tapping period to a small, undetected tempo change is in fact due to rapid internal phase correction, whereas slow adaptation of the relative phase of the taps is due to slow internal period correction.     

Perception of timing is more context sensitive than sensorimotor synchronization

In three experiments, the effects of contextual temporal variation on the perception of timing and on sensorimotor synchronization were examined. Experiment 1 showed that exposure to a variably timed auditory precursor sequence reduces the detectability of deviations from isochrony in a musical test sequence. By contrast, in Experiment 2 there was only a small and transient effect of identical precursor sequences on the variability of finger taps that were synchronized with a similar test sequence. Moreover, the precursor did not impede phase error correction following deviations from isochrony in the test sequence. Experiment 3 employed a within-subjects design that required simultaneous detection of irregularities in and synchronization with nonmusical auditory sequences. Precursor variability impaired only detection, not synchronization performance. These results suggest that perception of deviations from regularity engages context-sensitive tining processes, probably related to conscious awareness, that are not involved in sensorimotor synchronization.     

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.     

Postrecognition of interleaved melodies as an indirect measure of auditory stream formation

Primitive processes involved in auditory stream formation are measured with indirect, objective method. A target melody interleaved with a distractor sequence is followed by a probe melody that was identical to the target or differed by 2 notes. Listeners decided whether the probe melody was present or not in the composite sequence. Interleaved melody recognition is not possible when distractor sequences have the same mean frequency and maximum contour crossover with target melodies. Performance increases with mean frequency separation and timbral dissimilarity and is unaffected by the duration of the silent interval between composite sequence and probe melody. The relation between this indirect task measuring the interleaved melody recognition boundary and direct judgments measuring the fission boundary is discussed.     

Sensorimotor synchronization: the impact of temporally displaced auditory feedback

When subjects are asked to tap in synchrony to a regular sequence of stimulus events (e.g., clicks), performance is not perfect in that, usually, an anticipation of the tap is observed. The present study examines the influence of temporally displaced auditory feedback on the size of this anticipatory error. Whereas earlier studies have shown that this asynchrony exhibits a linear increase in size as a function of an increasing delay in such additional auditory feedback, this study compared the impact of shifting feedback forward in time (i.e., feedback presented before the tap) with that of delayed auditory feedback. Results showed that the impact of feedback displacement on the amount of asynchrony differed for positive and negative displacements. Delayed feedback led to an increase in asynchrony, whereas negative displacements had (almost) no effect. This finding is related to a model assuming that the various feedback components arising from the tap (tactile, kinesthetic, auditory) are integrated to form one central representation, and that the timing of this central representation arises from a linear combination of the components involved.     

Effect of practice on the identification of auditory sequences

Using a variant of the up-and-down method to establish duration thresholds for correct report of the order of sound sequences, six experiments were run with a practiced crew of three Ss. All showed striking improvement with practice, but substantial individual differences were observed. Two Ss found spaced sequences harder than simple cyclic ones and single presentations hardest of all, had increased difficulty when the component frequencies were brought closer together, and were disturbed by irregular timing. These variables made no difference to the third and most sensitive S, whose threshold reached 23 msec per component. All Ss displayed poorer performance if noise, additional signals, or a distrating activity occurred between the stimulus sequence and the response.