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This article was submitted to Auditory Cognitive Neuroscience, a section of the journal Frontiers in Psychology.
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Why do some people have problems “feeling the beat”? Here we investigate participants with congenital impairments in musical rhythm perception and production. A web-based version of the Montreal Battery of Evaluation of Amusia was used to screen for difficulties with rhythmic processing in a large sample and we identified three “dysrhythmic” individuals who scored below cut-off for the rhythm subtest, but not the pitch-based subtests. Follow-up testing in the laboratory was conducted to characterize the nature of both rhythm perception and production deficits in these dysrhythmic individuals. We found that they differed from control participants when required to synchronize their tapping to an external stimulus with a metrical pulse, but not when required to tap spontaneously (with no external stimulus) or to tap in time to an isochronous stimulus. Dysrhythmics exhibited a general tendency to tap at half the expected tempo when asked to synchronize to the beat of strongly metrical rhythms. These results suggest that the individuals studied here did not have motor production problems, but suffer from a selective rhythm perception deficit that influences the ability to entrain to metrical rhythms.
Rhythm perception and entrainment abilities develop early in human life (
The ability to perceive and entrain to a regular beat is considered to be a common and highly automatized human ability that can be measured using perceptual and motor tasks, both behaviourally and with neuroimaging techniques (
The most simple form of entrainment to a sensory (typically auditory) rhythmic stimulus involves perceiving and synchronizing movements with an isochronous beat with one level of periodicity, such as that produced by a metronome (
The induction of a perceived beat, or meter, in the listener by the use of temporal cues alone (i.e., in the absence of changes in pitch or sound intensity) has been demonstrated to rely upon certain phenomenal principles. Phenomenal accents are found to occur on tones that are followed or preceded by a relatively long “pause,” i.e., time between consecutive event onsets or inter-onset-intervals. The feeling of a meter can be induced by rather simple rhythmic sequences of identical tones, if those phenomenal accents occur regularly at a multiple of the underlying beat unit, for instance on every fourth beat (
Individuals with a developmental disorder termed “congenital amusia,” or “tone deafness,” are characterized by deficits in the perception of pitch-related features in musical melodies, which may or may not be accompanied by deficits in the perception of rhythm-related features. The diagnostic tool, the Montreal Battery of Evaluation of Amusia (MBEA;
Efforts to seek out people whose predominant difficulty lies in keeping in time, be it in conjunction with pitch deficits or in isolation, have been few and far between. A recent study reported on individuals who had problems with synchronization but not with rhythm perception (
In the present study we sought out individuals who exhibited specific impairments in rhythm perception according to the MBEA (administered on-line) and also self-reported difficulties with rhythm in everyday life. These individuals, whom we subsequently refer to as “dysrhythmic” were then tested to assess their ability to produce an isochronous tapping pulse (i) spontaneously, (ii) in time to isochronous stimulus sequences, and (iii) to sequences with strongly and weakly metrical-beats. In order to investigate the impact of pitch on these synchronization abilities, all three types of sequence were presented with and without pitch variation.
The MBEA was used to identify individuals with impairments that were specific to the rhythm subtest of the MBEA and associated with normal performance on the pitch-related subtests (scale, contour, interval). An online version of the scale and rhythm subtests was taken by 89,000 participants, and individuals scoring below the published cut-off scores for the rhythm subtest and above the cut-off score for the scale test (
Thirty eight control participants (18M, 20F; age range 19–61, mean = 38.92) were also identified from the online database for further inclusion in the present study. These individuals had scored above the published cut-off scores, both for the online MBEA subtests (scale and rhythm) as well as during laboratory-based testing (scale, contour, interval, rhythm subtests). In the tapping tasks, data for two dysrhythmic participants were not recorded for one trial due to a technical error; similarly, data were not recorded for eight trials in one control participant so that particular participant’s data are not included in any synchronization task analysis. All participants were reimbursed for travel expenses, and additionally received £7.50 for their time (approximately one hour).
All tapping tasks were performed using a DELL XPS M1530 computer running MAX/MSP 4.5 software. Stimuli were played to participants using an external Alesis IO2 soundcard and Sennheiser HD 265-1 headphones. Participants tapped on the computer keyboard using their preferred hand.
The strongly and weakly metrical rhythms used in the tapping tasks were of the same type as those developed by
Across all synchronization trials, the underlying tempo of rhythms was varied between 600ms and 700ms – both of these have been deemed to be comfortable tapping rates (
Random pitch variation was introduced throughout half of the trials to determine whether dysrhythmic participants experience further distraction given a pitch variation or not. Each sequence was presented once at a constant pitch and once with the random pitch variation. Random pitch variation was generated during the task and notes could take any semitone value within a two-octave scale. A full list of trial types is given in
Characteristics of the twelve rhythms used in the synchronization tapping tasks.
Trial | Rhythm | Tempo | Random pitch |
---|---|---|---|
1 | Isochronous | 600 | No |
2 | Isochronous | 700 | No |
3 | Isochronous | 600 | Yes |
4 | Isochronous | 700 | Yes |
5 | Strong no. 706 | 600 | No |
6 | Strong no. 737 | 700 | No |
7 | Strong no. 706 | 600 | Yes |
8 | Strong no. 737 | 700 | Yes |
9 | Weak no. 960 | 600 | No |
10 | Weak no. 1858 | 700 | No |
11 | Weak no. 960 | 600 | Yes |
12 | Weak no. 1858 | 700 | Yes |
Spontaneous tapping data were collected for all participants before they engaged in the synchronization tasks using acoustic stimuli. Participants were asked to tap at a comfortable pace and to make 40 taps (of which the first 10 were excluded from analysis).
In the synchronization tests, the instruction was to tap out a regular beat in synchrony with the rhythmic sequences that were played. This meant that for the sequences with an isochronous beat, participants were required to tap on every auditory event. For the strongly and weakly metrical rhythms in contrast, participants were required to extract the underlying beat and tap in time with this, meaning that not every tap made would align with an auditory event. The twelve different trials as outlined in
Each trial started with the presentation of eight initial beats during which the participant could listen to the stimulus and start tapping along if they wished to, but during which their tapping was not recorded. A timer bar on the screen indicated this familiarization period, at the end of which tapping started to be recorded.
Scores on the MBEA are given in
MBEA scores for dysrhythmic participants.
Subject | Scale | Contour | Interval | Rhythm | % Correct pitch (amalgamated) | % Correct rhythm |
---|---|---|---|---|---|---|
SS | 29 | 25 | 24 | 22 | 87 | 73 |
SWI | 28 | 30 | 27 | 21 | 94 | 70 |
VPO | 29 | 26 | 27 | 20 | 82 | 68 |
For the spontaneous tapping task, in which participants were asked to tap a regular beat in the absence of an acoustic stimulus, we analyzed the mean tapping rate, and variability in tapping rate for each individual. The first 10 taps were excluded from analysis, in order to given an adequate “lead-in” time for participants to start tapping at a regular rate. The individual mean tapping rate (in ms) was calculated for each participant. The standard deviation of the inter-tap-intervals (ITIs) for each participant was used as a measure of variance (in ms), and this value was divided by the individual’s mean tapping rate for that stimulus to give the coefficient of variation (CV) for spontaneous ITIs.
A summary of spontaneous tapping data from the dysrhythmic individuals compared to the controls is given in
We used a circular statistics approach to derive the mean asynchrony (a measure of tap time accuracy) of synchronization trials. The onset-asynchrony for each tap was captured as an error value relative to the position of the corresponding downbeat (i.e., how late or early the participant tapped in relation to the 40 downbeat locations in the acoustic stimuli). The individual tap-to-onset-asynchrony was transformed into a circular asynchrony by dividing by the most recent ITI and multiplying by 360. Circular statistics (e.g.,
To assess the ability to tap at the intended rate along to the stimuli we calculated the mean tapping rate and regularity of tapping rate. This was done by first dividing ITIs by the tempo of the trial to give relative tapping rates and enable comparison across the two tempi (excluding all outliers of more than 2.5 standard deviations from the sample mean ITI). One control participant’s data was excluded entirely, due to two trials in which all ITIs were outliers relative to the remaining participants’ data. Mean relative tapping rates for each condition are summarized in
The standard deviation of relative tapping rate (as calculated above) was used to measure an individual’s tapping stability within a trial. After log transformation in order to obtain normally distributed data samples, control data were compared across different conditions using a 3 (rhythm type: isochronous, strong, weak) × 2 (pitch: random variation, no pitch change) ANOVA, with Greenhouse–Geisser correction for non-sphericity. A significant main effect of rhythm condition was identified,
The dysrhythmics’ synchronization tapping data exhibited a qualitative difference in performance, identifiable at a gross level; while all three dysrhythmics often produced the correct number of taps for the isochronous sequences, they typically produced only half as many taps as there were downbeats for the strongly metrical rhythms. This might indicate that the dysrhythmics were tapping at half the tempo of the intended meter. The number of “missed beats,” i.e., the discrepancy between the 40 presented downbeats in the stimuli and the number of taps produced on each trial, are given in
Number of missed beats and mean ITIs in the dysrhythmic participants compared to the control group.
Measure | Participant | Trial 1 | Trial 2 | Trial 3 | Trial 4 | Trial 5 | Trial 6 | Trial 7 | Trial 8 | Trial 9 | Trial 10 | Trial 11 | Trial 12 |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Missed | SS | 0 | 0 | 9 | 0 | 11 | * | 13 | |||||
taps | SWI | 0 | 0 | 0 | 0 | * | 10 | 9 | 9 | ||||
VPO | 1 | 0 | 0 | 7 | 0 | 1 | 0 | 11 | 12 | 6 | 12 | ||
Control mean | 0.05 | 0.29 | 0.05 | 0.11 | 0.87 | 1.16 | 0.87 | 0.26 | 6.32 | 5.97 | 6.76 | 6.47 | |
Mean | SS | 600 | 704 | 770 | 701 | 389 | * | 882 | |||||
ITI (ms) | SWI | 605 | 704 | 604 | 703 | * | 943 | 795 | 926 | ||||
VPO | 614 | 713 | 600 | 1223 | 601 | 717 | 721 | 337 | 381 | 723 | 386 | ||
Control mean | 604 | 713 | 606 | 707 | 595 | 678 | 596 | 700 | 718 | 816 | 703 | 818 |
In weakly metrical trials, performance was comparably poor for all participants, with beats being “missed” frequently in both participant groups. It is clear from
The current study investigates individuals with what we are terming “dysrhythmia”: a congenital, selective deficit in rhythm perception and production. This deficit appears to be much rarer than the form of amusia that has been characterized as a selective pitch impairment. Importantly, the dysrhythmic participants studied here did not demonstrate a general problem with spontaneous tapping, indicating that these individuals are unlikely to suffer from motor deficits that could explain synchronization performance. Their difficulties with tapping along to the beat of different types of rhythm are thus likely to specifically relate to issues with extracting rhythmic information. In the present cases, both rhythm perception and production tasks revealed anomalies relative to the performance of the controls, including both an impairment in musical rhythm perception, measured via the MBEA, and abnormal tapping behavior when required to extract the beat from a rhythmic sequence.
If beat-based rhythm production was generally impaired in dysrhythmic subjects then we would expect to also find difficulties in the maintenance of a self-paced steady beat. However, no difference in spontaneous tapping rate was found between control subjects and the dysrhythmics, apart from slightly larger variability in tapping rate for one dysrhythmic compared to the controls. Overall, the normal ability of these individuals to produce a self-paced steady beat demonstrates that rhythmic difficulties cannot be ascribed to motor deficits with generating and maintaining a steady beat. One might expect, therefore, that dysrhythmics would be able to perform normally if required to continue tapping out an isochronous beat after entraining with an acoustic stimulus. Their problem seems to lie specifically in extracting the correct (intended) meter from non-isochronous metrical rhythms. This differentiation merits future investigation.
Consistent with the notion of a close-to normal ability to produce a steady beat, basic sensorimotor entrainment was largely preserved: for synchronization with an isochronous beat, tapping rates in dysrhythmic participants (
The finding of entraining at an unexpected metrical level is very similar to that of
Either way, this problem is quite different from “poor synchronizers” as identified by
To our knowledge, this is the first report of a type of musical deficit that demonstrates impaired rhythm perception and beat extraction in the face of intact pitch perception, in neurologically intact individuals. This pattern is the opposite of that which has previously been reported in individuals termed congenitally amusic, according to the MBEA, where as many as half are reported to have pitch deficits in the face of normal scores on the rhythm test (
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.