Isochronous Tone Sequences Research Articles

Memory-Paced Tapping to Auditory Rhythms: Effects of Rate, Speech, and Motor Engagement.

Humans have a near-automatic tendency to entrain their motor actions to rhythms in the environment. Entrainment has been hypothesized to play an important role in processing naturalistic stimuli, such as speech and music, which have intrinsically rhythmic properties. Here, we studied two facets of entraining one's rhythmic motor actions to an external stimulus: (a) synchronized finger tapping to auditory rhythmic stimuli and (b) memory-paced reproduction of a previously heard rhythm. Using modifications of the Synchronization-Continuation tapping paradigm, we studied how these two rhythmic behaviors were affected by different stimulus and task features. We tested synchronization and memory-paced tapping for a broad range of rates, from stimulus onset asynchrony of subsecond to suprasecond, both for strictly isochronous tone sequences and for rhythmic speech stimuli (counting from 1 to 10), which are more ecological yet less isochronous. We also asked what role motor engagement plays in forming a stable internal representation for rhythms and guiding memory-paced tapping. Our results show that individuals can flexibly synchronize their motor actions to a very broad range of rhythms. However, this flexibility does not extend to memory-paced tapping, which is accurate only in a narrower range of rates, around ~1.5 Hz. This pattern suggests that intrinsic rhythmic defaults in the auditory and/or motor system influence the internal representation of rhythms, in the absence of an external pacemaker. Interestingly, memory-paced tapping for speech rhythms and simple tone sequences shared similar "optimal rates," although with reduced accuracy, suggesting that internal constraints on rhythmic entrainment generalize to more ecological stimuli. Last, we found that actively synchronizing to tones versus passively listening to them led to more accurate memory-paced tapping performance, which emphasizes the importance of action-perception interactions in forming stable entrainment to external rhythms.

Effect of Auditory Predictability on the Human Peripheral Auditory System.

Auditory perception is facilitated by prior knowledge about the statistics of the acoustic environment. Predictions about upcoming auditory stimuli are processed at various stages along the human auditory pathway, including the cortex and midbrain. Whether such auditory predictions are processed also at hierarchically lower stages—in the peripheral auditory system—is unclear. To address this question, we assessed outer hair cell (OHC) activity in response to isochronous tone sequences and varied the predictability and behavioral relevance of the individual tones (by manipulating tone-to-tone probabilities and the human participants’ task, respectively). We found that predictability alters the amplitude of distortion-product otoacoustic emissions (DPOAEs, a measure of OHC activity) in a manner that depends on the behavioral relevance of the tones. Simultaneously recorded cortical responses showed a significant effect of both predictability and behavioral relevance of the tones, indicating that their experimental manipulations were effective in central auditory processing stages. Our results provide evidence for a top-down effect on the processing of auditory predictability in the human peripheral auditory system, in line with previous studies showing peripheral effects of auditory attention.

Beat-induced fluctuations in auditory cortical beta-band activity: using EEG to measure age-related changes.

People readily extract regularity in rhythmic auditory patterns, enabling prediction of the onset of the next beat. Recent magnetoencephalography (MEG) research suggests that such prediction is reflected by the entrainment of oscillatory networks in the brain to the tempo of the sequence. In particular, induced beta-band oscillatory activity from auditory cortex decreases after each beat onset and rebounds prior to the onset of the next beat across tempi in a predictive manner. The objective of the present study was to examine the development of such oscillatory activity by comparing electroencephalography (EEG) measures of beta-band fluctuations in 7-year-old children to adults. EEG was recorded while participants listened passively to isochronous tone sequences at three tempi (390, 585, and 780 ms for onset-to-onset interval). In adults, induced power in the high beta-band (20–25 Hz) decreased after each tone onset and rebounded prior to the onset of the next tone across tempo conditions, consistent with MEG findings. In children, a similar pattern was measured in the two slower tempo conditions, but was weaker in the fastest condition. The results indicate that the beta-band timing network works similarly in children, although there are age-related changes in consistency and the tempo range over which it operates.

Hear it playing low and slow: How pitch level differentially influences time perception

Variations in both pitch and time are important in conveying meaning through speech and music, however, research is scant on perceptual interactions between these two domains. Using an ordinal comparison procedure, we explored how different pitch levels of flanker tones influenced the perceived duration of empty interstimulus intervals (ISIs). Participants heard monotonic, isochronous tone sequences (ISIs of 300, 600, or 1200ms) composed of either one or five standard ISIs flanked by 500Hz tones, followed by a final interval (FI) flanked by tones of either the same (500Hz), higher (625Hz), or lower (400Hz) pitch. The FI varied in duration around the standard ISI duration. Participants were asked to determine if the FI was longer or shorter in duration than the preceding intervals. We found that an increase in FI flanker tone pitch level led to the underestimation of FI durations while a decrease in FI flanker tone pitch led to the overestimation of FI durations. The magnitude of these pitch-level effects decreased as the duration of the standard interval was increased, suggesting that the effect was driven by differences in mode-switch latencies to start/stop timing. Temporal context (One vs. Five Standard ISIs) did not have a consistent effect on performance. We propose that the interaction between pitch and time may have important consequences in understanding the ways in which meaning and emotion are communicated.

A Bayesian Framework for the Perceived Timing of Rhythmic Stimuli

Sequences of regularly spaced stimuli carry information about the timing and properties of future stimuli. Here we investigated how these expectations can affect the perceived time of stimuli and we propose a model based on the Bayesian framework. Expectation of when a future stimulus is to occur is modelled as the prior probability of a stimulus over future time. The prior is integrated with the current sensory evidence (likelihood function) to give rise to our perception, which is based on the posterior distribution. Stimuli appearing earlier than expected should then be perceptually delayed towards the peak of the prior distribution whereas stimuli presented later than expected should be anticipated. As expectations increase, for example when longer sequences are presented, the prior should become steeper and should have more influence on the perceived timing of stimuli. A second assumption of the model is that the prior should be built within every trial and is not only formed over the course experiment.In order to test the predictions of the model, we presented participants with isochronous tone sequences with an inter-stimulus interval (ISI) of 700ms. Participants reported whether the last stimulus was presented before or after a visual temporal probe. In such a way we could find the audiovisual asynchrony at which the two stimuli are perceived to be synchronous and measure any temporal distortion due to the prior. Importantly, the final stimulus was presented slightly earlier, on time, or later than expected to measure the effect of the prior.In accordance with the predictions, we find that stimuli presented earlier than expected are indeed delayed, and stimuli presented late are perceptually anticipated. However, we also find that stimuli that are presented on time are anticipated, a prediction not directly evident in the model. This could be due to a general anticipation of expected stimuli by an effect similar to prior entry, which is absent for stimuli presented too early. This effect could be modelled as the reliance on a hazard function, rather than on probability distributions. As the number of repeated stimuli increases, we observe that both the delay and the anticipation effects increase in magnitude following the predictions of the model.In another experiment we tested whether prior expectations can be built within a single trial by presenting sequences of 4 stimuli spaced at 3 different ISIs (400, 700, and 1000ms). The ISIs were randomly selected at every trial. Although participants could not know which ISI will be presented based on the previous trial, they could still generate an expectation for when a stimulus should occur based on the timing of the sequence presented on the trial. Results showed the same type of effect, namely a shift of stimuli towards expectation thus suggesting that the brain ‘resets’ after each sequence and calculates temporal expectations within each trial at least to some extent.

Rhythm sensitivity in macaque monkeys

This study provides evidence that monkeys are rhythm sensitive. We composed isochronous tone sequences consisting of repeating triplets of two short tones and one long tone which humans perceive as repeating triplets of two weak and one strong beat. This regular sequence was compared to an irregular sequence with the same number of randomly arranged short and long tones with no such beat structure. To search for indication of rhythm sensitivity we employed an oddball paradigm in which occasional duration deviants were introduced in the sequences. In a pilot study on humans we showed that subjects more easily detected these deviants when they occurred in a regular sequence. In the monkeys we searched for spontaneous behaviors the animals executed concomitant with the deviants. We found that monkeys more frequently exhibited changes of gaze and facial expressions to the deviants when they occurred in the regular sequence compared to the irregular sequence. In addition we recorded neuronal firing and local field potentials from 175 sites of the primary auditory cortex during sequence presentation. We found that both types of neuronal signals differentiated regular from irregular sequences. Both signals were stronger in regular sequences and occurred after the onset of the long tones, i.e., at the position of the strong beat. Local field potential responses were also significantly larger for the durational deviants in regular sequences, yet in a later time window. We speculate that these temporal pattern-selective mechanisms with a focus on strong beats and their deviants underlie the perception of rhythm in the chosen sequences.

Anticipatory phase correction in sensorimotor synchronization

Studies of phase correction in sensorimotor synchronization often introduce timing perturbations that are unpredictable with regard to direction, magnitude, and position in the stimulus sequence. If participants knew any or all of these parameters in advance, would they be able to anticipate perturbations and thus regain synchrony more quickly? In Experiment 1, we asked musically trained participants to tap in synchrony with short isochronous tone sequences containing a phase shift (PS) of −100, −40, 40, or 100ms and provided advance information about its direction, position, or both (but not about its magnitude). The first two conditions had little effect, but in the third condition participants shifted their tap in anticipation of the PS, though only by about ±40ms on average. The phase correction response to the residual PS was also enhanced. In Experiment 2, we provided complete advance information about PSs of various magnitudes either at the time of the immediately preceding tone (“late”) or at the time of the tone one position back (“early”) while also varying sequence tempo. Anticipatory phase correction was generally conservative and was impeded by fast tempo in the “late” condition. At fast tempi in both conditions, advancing a tap was more difficult than delaying a tap. The results indicate that temporal constraints on anticipatory phase correction resemble those on reactive phase correction. While the latter is usually automatic, this study shows that phase correction can also be controlled consciously for anticipatory purposes.

No Sustained Sound Illusion in Rhythmic Sequences

Recent research has shown that subdivision of intervals between beats makes the beat tempo seem slower—a "divided time illusion" (DTI) in music. Another temporal illusion described in the psychophysical literature is that a sustained sound seems longer than a silent interval of the same duration. This "sustained sound illusion" (SSI) may be due to acceleration of an internal pacemaker by continuous sound, or it may result from slower perception of sound offsets than of sound onsets. Experiment 1 tested the pacemaker acceleration hypothesis in a rhythmic context by asking musicians to compare or reproduce the tempi of isochronous tone sequences played legato ("filled") or staccato ("unfilled"). There was no indication that legato sequences were perceived as slower than staccato sequences. Experiment 2 tested the delayed offset perception hypothesis by asking musicians to judge the relative time of occurrence of abrupt or decaying tone offsets in the interonset intervals of isochronous sequences. There was no evidence of delayed perception of abrupt offsets, and decaying offsets were perceived only slightly late. These results suggest that the SSI, unlike the DTI, does not occur in rhythmic contexts and thus is probably not of musical relevance. More generally, the results challenge some proposed explanations of this illusion and call for further research on the conditions under which it does occur.

No Sustained Sound Illusion in Rhythmic Sequences

Recent Research has shown that subdivision of intervals between beats makes the beat tempo seem slower—a "divided time illusion" (DTI) in music. Another temporal illusion described in the psychophysical literature is that a sustained sound seems longer than a silent interval of the same duration. This "sustained sound illusion" (SSI) may be due to acceleration of an internal pacemaker by continuous sound, or it may result from slower perception of sound offsets than of sound onsets. Experiment 1 tested the pacemaker acceleration hypothesis in a rhythmic context by asking musicians to compare or reproduce the tempi of isochronous tone sequences played legato ("filled") or staccato ("unfilled"). There was no indication that legato sequences were perceived as slower than staccato sequences. Experiment 2 tested the delayed offset perception hypothesis by asking musicians to judge the relative time of occurrence of abrupt or decaying tone offsets in the interonset intervals of isochronous sequences. There was no evidence of delayed perception of abrupt offsets, and decaying offsets were perceived only slightly late. These results suggest that the SSI, unlike the DTI, does not occur in rhythmic contexts and thus is probably not of musical relevance. More generally, the results challenge some proposed explanations of this illusion and call for further research on the conditions under which it does occur.

Age-related differences in discrimination of temporal intervals in accented tone sequences

The study measured listener sensitivity to increments of a target inter-onset interval (IOI) embedded within isochronous tone sequences that featured a single accented tonal component. The sequences consisted of six 1000-Hz tone bursts separated by silent intervals to establish equal tonal IOIs of 200 ms within the sequence. Tone burst durations within the sequences were 50 ms, except one tone had a longer duration of 100 ms to produce a perception of accent. Duration DLs in ms for increments of a single sequence IOI were measured adaptively by adjusting the duration of the silent interval between two tones. Sequence position of the target IOI differed across conditions. Listeners included young normal-hearing adults and older adults with and without hearing loss. Discrimination performance of the two older listener groups was equivalent and significantly poorer than that of the younger listeners in each discrimination condition. The age-related discrimination deficits were independent of sequence locations of both the target interval and the accented tonal component. Comparative DLs collected for target intervals in unaccented tone sequences with equal tone durations revealed that the detrimental effects of accent on temporal discrimination were primarily restricted to the older listeners.

Picking up the pace: Effects of global temporal context on sensitivity to the tempo of auditory sequences

This article continues a line of research examining factors affecting listeners' auditory tempo sensitivities. Of particular interest is the question of whether listeners are sensitive to the overall (global) pace of their auditory environment and how this sensitivity may affect their perceptions of sequence timing. To address this question, we manipulated the set of sequence tempi (between 300 and 700 msec) that listeners experienced over the course of a 1-h period (i.e., the global temporal context) while they performed a tempo-discrimination task involving standard-comparison pairs of isochronous tone sequences. Overall findings show systematic distortions in perceived tempo that are consistent with the view that listeners adapt to the global pace of their auditory environments. Moreover, general support was found for the hypothesis that increasing the number of equal intervals in a standard sequence produces greater improvements in tempo sensitivity when the standard sequence tempo is different from the global pace than when it is at the global pace. Implications of these findings for models of timing and temporal processing are discussed.

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.

Tempo sensitivity in isochronous tone sequences: The multiple-look model revisited

Factors affecting tempo sensitivity in isochronous tone sequences were investigated in two experiments. Participants listened to tones in sequence conditions in which the number of time intervals in isochronous standard and comparison sequences was varied, and they were asked to judge the tempo of the comparison relative to the standard. When the duration of the standard interval was held constant, tempo sensitivity was affected by the number of comparison intervals, but not by the number of standard intervals. In contrast, when the duration of the standard interval was varied randomly from trial to trial, tempo sensitivity was affected by the number of intervals in both sequences. The present findings are discussed in the context of a generalized multiple-look model that posits independent contributions of both sequences to tempo sensitivity. Quantitative model fits suggest that the relative contribution of the number of the standard intervals to tempo thresholds depends on (1) the availability of a stable long-term referent for the standard tempo and (2) a priori knowledge about the number of standard intervals.

Tempo discrimination of isochronous tone sequences: The multiple-look model revisited

Previous research has shown that increasing the number of intervals in an isochronous tone sequence reduces tempo discrimination thresholds [C. Drake and M. Botte, Percept. Psychophys. 54, 277–286 (1993)]. One question that arises is whether increased tempo sensitivity in this instance is attributed to multiple looks at the standard interval, comparison interval, or both. The present study addressed this question by examining tempo discrimination using isochronous tone sequences that contained variable numbers of standard and comparison intervals. In all cases, participants judged the tempo of the comparison sequence relative to a standard sequence (responding faster or slower). Preliminary results suggest that in some cases increases in tempo sensitivity are more due to repetitions of the comparison interval than to repetitions of the standard. The implications of these findings for theories of auditory tempo discrimination will be discussed.

Periodicity, Pattern Formation, and Metric Structure

This article describes an approach to metrical structure focussing on its role as an active listening strategy. The theory postulates that metrical structure is a self-organized, dynamic structure composed of self-sustaining oscillations. The emergence of this structural representation is modeled as a pattern formation process whose the neural correlate is the formation of a spatiotemporal pattern of neural activity. The primary function of the dynamic structure is attentional. It enables anticipation of future events thus, targeting of perception, and coordination of action with exogenous events. Stability and flexibility properties arise through nonlinearities in the underlying pattern-forming dynamics. Furthermore, this dynamic representation functions in musical communication. Transient stimulus fluctuations observed in musical performance (e.g., rate changes, intonation) are not noise, but rather communicate structural information, intention, and affect. These communicative gestures are recognized as deviations from temporal expectations embodied in the metrical structure. Experiments are reviewed that investigate stimuli of varying complexity, from simple isochronous tone sequences to performed music, and the model’s success at capturing these data is assessed.

Resonance in the Perception of Musical Pulse

A number of phenomena related to the perception of isochronous tone sequences peak at a certain rate (or tempo) and taper off at both slower and faster rates. In the present paper we start from the hypothesis that the peaking finds its origin in the presence of a damped resonating oscillator in the perceptual-motor system. We assume that for pulse perception only the ‘effective’ resonance curve matters, i.e., the enhancement of the amplitude of the oscillator beyond the critical damping. On the basis of the effective resonance curve, analyses have been made of data of Vos (1973) on subjective rhythmization and of data on tapping along isochronous tone sequences (Parncutt, 1994) and polyrhythmic sequences (Handel & Oshinsky, 1981). The results show that these data can be very well approximated with the proposed model. The best results are obtained with a resonance period of 500-550 ms and a width at half height of about 400-800 ms. A comparison is made with a number of other tempo related phenomena. In the second part a preliminary effort is made to determine the distribution of perceived tempi of musical pieces heard on the radio and in recordings of several styles, by having a number of listeners tapping along these pieces. The resonance curve appears to be a good tool to characterize these distributions.

Effect of deviations from temporal expectations on tempo discrimination of isochronous tone sequences.

The effect of deviations from temporal expectations on tempo discrimination was studied in 3 experiments using isochronous auditory sequences. Temporal deviations consisted of advancing or delaying the onset of a comparison pattern relative to an "expected" onset, defined by an extension of the periodicity of a preceding standard pattern. An effect of onset condition was most apparent when responses to faster and slower comparison patterns were analyzed separately and onset conditions were mixed. Under these conditions, early onsets produced more "faster" judgments and lower thresholds for tempo increases, and late onsets produced more "slower" judgments and lower thresholds for tempo decreases. In another experiment, pattern tempo had a similar effect: Fast tempos led to lower thresholds for tempo increases and slow tempos led to lower thresholds for tempo decreases. Findings support oscillator-based approaches to time discrimination.

Effect of deviations from temporal expectations on tempo discrimination of isochronous tone sequences.

Effect of deviations from temporal expectations on tempo discrimination of isochronous tone sequences.