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     

Delayed auditory feedback in repetitive tapping: A role for the sensory goal

The open-loop model by Wing and Kristofferson has successfully explained many aspects of movement timing. A later adaptation of the model assumes that timing processes do not control the movements themselves, but the sensory consequences of the movements. The present study tested direct predictions from this “sensory-goals model”. In two experiments, participants were instructed to produce regular intervals by tapping alternately with the index fingers of the left and the right hand. Auditory feedback tones from the taps of one hand were delayed. As a consequence, regular intervals between taps resulted in irregular intervals between feedback tones. Participants compensated for this auditory irregularity by changing their movement timing. Compensation effects increased with the magnitude of feedback delay (Experiment 1) and were also observed in a unimanual variant of the task (Experiment 2). The pattern of effects in alternating tapping suggests that compensation processes were anticipatory—that is, compensate for upcoming feedback delay rather than being reactions to delay. All experiments confirmed formal model predictions. Taken together, the findings corroborate the sensory-goals adaptation of the Wing–Kristofferson model.     

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.     

FTAP: A Linux-based program for tapping and music experiments

This paper describes FTAP, a flexible data collection system for tapping and music experiments. FTAP runs on standard PC hardware with the Linux operating system and can process input keystrokes and auditory output with reliable millisecond resolution. It uses standard MIDI devices for input and output and is particularly flexible in the area of auditory feedback manipulation. FTAP can run a wide variety of experiments, including synchronization/continuation tasks (Wing & Kristofferson, 1973), synchronization tasks combined with delayed auditory feedback (Aschersleben & Prinz, 1997), continuation tasks with isolated feedback perturbations (Wing, 1977), and complex alterations of feedback in music performance (Finney, 1997). Such experiments have often been implemented with custom hardware and software systems, but with FTAP they can be specified by a simple ASCII text parameter file. FTAP is available at no cost in source-code form.     

Does an auditory distractor sequence affect self-paced tapping?

This study investigated whether an auditory distractor (D) sequence affects the timing of self-paced finger tapping. To begin with, Experiment 1 replicated earlier findings by showing that, when taps are synchronized with an isochronous auditory target (T) sequence, an isochronous D sequence of different tempo and pitch systematically modulates the tap timing. The extent of the modulation depended on the relative intensity of the T and D tones, but not on their pitch distance. Experiment 2 then used a synchronization-continuation paradigm in which D sequences of different tempi were introduced only during continuation tapping. Although the D sequences rarely captured the taps completely, they did increase the tapping variability and deviations from the correct tempo. Furthermore, they eliminated the negative correlation between successive inter-tap intervals and led to intermittent phase locking when the tapping period was close to the period of the D sequence. These distractor effects occurred regardless of whether or not the taps generated auditory feedback tones. The distractor effects thus depend neither on the intention to synchronize with a T sequence nor on the simultaneous perception of two auditory sequences. Rather, they seem to reflect a basic attraction of rhythmic movement to auditory rhythms.     

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.     

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.     

Timing and aging: slowing of fastest regular tapping rate with preserved timing error detection and correction

This study assessed motor limits of regular tapping, timing error detection, and correction in 60 participants aged from 19 to 98 years. Rate limitations on motor production were estimated from the average inter-tap interval when tapping as fast as possible for 30 s. Timing error detection required participants to judge whether a sound sequence presented at a slow, intermediate, or fast speed contained an irregularity because of phase shift. This was performed with or without synchronizing to the sounds. On the basis of the just-detectable positive phase shift (JND), participants synchronized with sequences containing phase shifts that were subliminal, just detectable or supraliminal. On average, JNDs were 9% of the inter-onset interval and by and large were not affected by synchronization tapping. Speed of error correction was estimated from the number of tones to return within 20% of the preshift synchronization error. Consistent with previous findings of motor slowing with aging, the fastest inter-tap interval increased with age. However, there was no age-related decline in JNDs or speed of error correction, both of which reflect predictive abilities for intervals within the motor repertoire of human adults. These results point towards intact timing error processing up to an advanced age. In assessing timing abilities in the brain of older adults, it is important to differentiate between motor slowing and its impact on rhythmic behavior (e.g., walking pace) from anticipatory mechanisms ('what to expect when') and how these are used to adjust the timing of actions ('what to do when').     

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.     

Ideomotor effects of pitch on continuation tapping

The ideomotor principle predicts that perception will modulate action where overlap exists between perceptual and motor representations of action. This effect is demonstrated with auditory stimuli. Previous perceptual evidence suggests that pitch contour and pitch distance in tone sequences may elicit tonal motion effects consistent with listeners' implicit awareness of the lawful dynamics of locomotive bodies. To examine modulating effects of perception on action, participants in a continuation tapping task produced a steady tempo. Auditory tones were triggered by each tap. Pitch contour randomly and persistently varied within trials. Pitch distance between successive tones varied between trials. Although participants were instructed to ignore them, tones systematically affected finger dynamics and timing. Where pitch contour implied positive acceleration, the following tap and the intertap interval (ITI) that it completed were faster. Where pitch contour implied negative acceleration, the following tap and the ITI that it completed were slower. Tempo was faster with greater pitch distance. Musical training did not predict the magnitude of these effects. There were no generalized effects on timing variability. Pitch contour findings demonstrate how tonal motion may elicit the spontaneous production of accents found in expressive music performance.     

Reduced timing variability during bimanual coupling: A role for sensory information

On a repetitive tapping task, the within-hand variability of intertap intervals is reduced when participants tap with two hands as compared to one-hand tapping. Because this bimanual advantage can be attributed to timer variance (Wing-Kristofferson model, 1973a, b), separate timers have been proposed for each hand, whose outputs are then averaged (Helmuth & Ivry, 1996). An alternative notion is that action timing is based on its sensory reafferences (Aschersleben & Prinz, 1995; Prinz, 1990). The bimanual advantage is then due to increased sensory reafference. We studied bimanual tapping with the continuation paradigm. Participants first synchronized their taps with a metronome and then continued without the pacing signal. Experiment 1 replicated the bimanual advantage. Experiment 2 examined the influence of additional sensory reafferences. Results showed a reduction of timer variance for both uni- and bimanual tapping when auditory feedback was added to each tap. Experiment 3 showed that the bimanual advantage decreased when auditory feedback was removed from taps with the left hand. Results indicate that the sensory reafferences of both hands are used and integrated into timing. This is consistent with the assumption that the bimanual advantage is at least partly due to the increase in sensory reafference. A reformulation of the Wing-Kristofferson model is proposed to explain these results, in which the timer provides action goals in terms of sensory reafferences.     

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.     

Self-induced versus reactive triggering of synchronous movements in a deafferented patient and control subjects

The present study investigates the contribution of tactile-kinesthetic information to the timing of movements. The relative timing of simultaneous tapping movements of finger and foot (hand-foot asynchrony) was examined in a simple reaction time task and in discrete self-initiated taps (Experiment 1), and in externally triggered synchronization tapping (Experiment 2). We compared the performance of a deafferented participant (IW) to the performance of two control groups of different ages. The pattern of results in control groups replicates previous findings: Whereas positive hand-foot asynchronies (hand precedes foot) are observed in a simultaneous reaction to an auditory stimulus, hand-foot asynchronies are negative with discrete self-initiated as well as auditorily paced sequences of synchronized finger and foot taps. In the first case, results are explained by a simultaneous triggering of motor commands. In contrast, self-initiated and auditorily paced movements are assumed to be controlled in terms of their afferent consequences, as provided by tactile-kinesthetic information. The performance of the deafferented participant differed from that of healthy participants in some aspects. As expected on the basis of unaffected motor functions, the participant was able to generate finger and foot movements in reaction to an external signal. In spite of the lack of movement-contingent sensory feedback, the deafferented participant showed comparable timing errors in self-initiated and regularly paced tapping as observed in control participants. However, in discrete self-initiated taps IW's hand-foot asynchronies were considerably larger than in control participants, while performance did not differ from that of controls in continuous movement generation. These findings are discussed in terms of an internal generation of the movement's sensory consequences (forward-modeling).     

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.     

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.     

On the nature of phase attraction in sensorimotor synchronization with interleaved auditory sequences

In a task that requires in-phase synchronization of finger taps with an isochronous sequence of target tones that is interleaved with a sequence of distractor tones at various fixed phase relationships, the taps tend to be attracted to the distractor tones, especially when the distractor tones closely precede the target tones [Repp, B. H. (2003a). Phase attraction in sensorimotor synchronization with auditory sequences: Effects of single and periodic distractors on synchronization accuracy. Journal of Experimental Psychology: Human Perception and Performance, 29, 290-309]. The present research addressed two related questions about this distractor effect: (1) Is it a function of the absolute temporal separation or of the relative phase of the two stimulus sequences? (2) Is it the result of perceptual grouping (integration) of target and distractor tones or of simultaneous attraction to two independent sequences? In three experiments, distractor effects were compared across two different sequence rates. The results suggest that absolute temporal separation, not relative phase, is the critical variable. Experiment 3 also included an anti-phase tapping task that addressed the second question directly. The results suggest that the attraction of taps to distractor tones is caused mainly by temporal integration of target and distractor tones within a fixed window of 100-150 ms duration, with the earlier-occurring tone being weighted more strongly than the later-occurring one.     

Spectral decomposition of variability in synchronization and continuation tapping: comparisons between auditory and visual pacing and feedback conditions

Spectral analysis was applied to study the variability in human rhythmic synchronization to a visual, auditory or combined auditory-visual metronome of about 2 Hz, as well as the variability in continuation tapping at the same rate with or without visual or auditory feedback. In synchronization, variability was larger in the visual condition than in the auditory and combined conditions, but only below frequencies of about 0.3 Hz. Thus, there seem to be at least two sources of variability in synchronization, one being modality-independent and limited to intervals shorter than 3 s, and the other being modality-dependent and evident as slow "drift", especially in the visual task. In continuation tapping, variability did not depend reliably on the presence or modality of feedback. However, spectral analysis revealed a change in the temporal structure of variability around 0.08 Hz (a period of about 12 s or 24 taps), which roughly agrees with earlier findings reported in the literature.     

Timing dysfunctions in schizophrenia as measured by a repetitive finger tapping task

Schizophrenia may be associated with a fundamental disturbance in the temporal coordination of information processing in the brain, leading to classic symptoms of schizophrenia such as thought disorder and disorganized and contextually inappropriate behavior. Although a variety of behavioral studies have provided strong evidence for perceptual timing deficits in schizophrenia, no study to date has directly examined overt temporal performance in schizophrenia using a task that differentially engages perceptual and motor-based timing processes. The present study aimed to isolate perceptual and motor-based temporal performance in individuals diagnosed with schizophrenia using a repetitive finger-tapping task that has previously been shown to differentially engage brain regions associated with perceptual and motor-related timing behavior. Thirty-two individuals with schizophrenia and 31 non-psychiatric control participants completed the repetitive finger-tapping task, which required participants to first tap in time with computer-generated tones separated by a fixed intertone interval (tone-paced tapping), after which the tones were discontinued and participants were required to continue tapping at the established pace (self-paced tapping). Participants with schizophrenia displayed significantly faster tapping rates for both tone- and self-paced portions of the task compared to the non-psychiatric group. Individuals diagnosed with schizophrenia also displayed greater tapping variability during both tone- and self-paced portions of the task. The application of a mathematical timing model further indicated that group differences were primarily attributable to increased timing – as opposed to task implementation – difficulties in the schizophrenia group, which is noteworthy given the broad range of impairments typically associated with the disorder. These findings support the contention that schizophrenia is associated with a broad range of timing difficulties, including those associated with time perception as well as time production.     

Compensation for subliminal timing perturbations in perceptual-motor synchronization

 It is sometimes assumed that limits of temporal discrimination established in psychophysical tasks constrain the timing information available for the control of action. Results from the five perceptual-motor synchronization experiments presented here argue against this assumption. Experiment 1 demonstrates that subliminal (0.8–2%) local changes in interval duration in an otherwise isochronous auditory sequence are rapidly compensated for in the timing of synchronized finger tapping. If this compensation is based on perception of the highly variable synchronization error (SE) rather than of the local change in stimulus period, then it could be based solely on SEs that exceed the temporal order threshold. However, that hypothesis is ruled out by additional analyses of Exp. 1 and the results of Exp. 2, a combined synchronization and temporal order judgment task. Experiments 3–5 further show that three factors that affect the detectability of local deviations from stimulus isochrony do not inhibit effective compensation for such deviations in synchronized tapping. Experiment 5, a combined synchronization and detection task, shows directly that compensation for timing perturbations does not depend on explicit detection. Overall, the results suggest that the automatic processes involved in the temporal control of action have access to more accurate timing information than do the conscious decision processes of auditory temporal judgment. Received: 19 November 1998 / Accepted: 18 March 1999