Electrical Brain Responses to Beat Irregularities in Two Cases of Beat Deafness.

Beat deafness, a recently documented form of congenital amusia, provides a unique window into functional specialization of neural circuitry for the processing of musical stimuli: Beat-deaf individuals exhibit deficits that are specific to the detection of a regular beat in music and the ability to move along with a beat. Studies on the neural underpinnings of beat processing in the general population suggest that the auditory system is capable of pre-attentively generating a predictive model of upcoming sounds in a rhythmic pattern, subserved largely within auditory cortex and reflected in mismatch negativity (MMN) and P3 event-related potential (ERP) components. The current study examined these neural correlates of beat perception in two beat-deaf individuals, Mathieu and Marjorie, and a group of control participants under conditions in which auditory stimuli were either attended or ignored. Compared to control participants, Mathieu demonstrated reduced behavioral sensitivity to beat omissions in metrical patterns, and Marjorie showed a bias to identify irregular patterns as regular. ERP responses to beat omissions reveal an intact pre-attentive system for processing beat irregularities in cases of beat deafness, reflected in the MMN component, and provide partial support for abnormalities in later cognitive stages of beat processing, reflected in an unreliable P3b component exhibited by Mathieu-but not Marjorie-compared to control participants. P3 abnormalities observed in the current study resemble P3 abnormalities exhibited by individuals with pitch-based amusia, and are consistent with attention or auditory-motor coupling accounts of deficits in beat perception.

Excitability of the motor system: A transcranial magnetic stimulation study on singing and speaking.

The perception of movements is associated with increased activity in the human motor cortex, which in turn may underlie our ability to understand actions, as it may be implicated in the recognition, understanding and imitation of actions. Here, we investigated the involvement and lateralization of the primary motor cortex (M1) in the perception of singing and speech. Transcranial magnetic stimulation (TMS) was applied independently for both hemispheres over the mouth representation of the motor cortex in healthy participants while they watched 4-s audiovisual excerpts of singers producing a 2-note ascending interval (singing condition) or 4-s audiovisual excerpts of a person explaining a proverb (speech condition). Subjects were instructed to determine whether a sung interval/written proverb, matched a written interval/proverb. During both tasks, motor evoked potentials (MEPs) were recorded from the contralateral mouth muscle (orbicularis oris) of the stimulated motor cortex compared to a control task. Moreover, to investigate the time course of motor activation, TMS pulses were randomly delivered at 7 different time points (ranging from 500 to 3500 ms after stimulus onset). Results show that stimulation of the right hemisphere had a similar effect on the MEPs for both the singing and speech perception tasks, whereas stimulation of the left hemisphere significantly differed in the speech perception task compared to the singing perception task. Furthermore, analysis of the MEPs in the singing task revealed that they decreased for small musical intervals, but increased for large musical intervals, regardless of which hemisphere was stimulated. Overall, these results suggest a dissociation between the lateralization of M1 activity for speech perception and for singing perception, and that in the latter case its activity can be modulated by musical parameters such as the size of a musical interval.

Language familiarity, expectation, and novice musical rhythm production.

The music of expert musicians reflects the speech rhythm of their native language. Here, we examine this effect in amateur and novice musicians. English- and French-speaking participants were both instructed to produce simple "English" and "French" tunes using only two keys on a keyboard. All participants later rated the rhythmic variability of English and French speech samples. The rhythmic variability of the "English" and "French" tunes that were produced reflected the perceived rhythmic variability in English and French speech samples. Yet, the pattern was different for English and French participants and did not correspond to the actual measured speech rhythm variability of the speech samples. Surprise recognition tests two weeks later confirmed that the music-speech relationship remained over time. The results show that the relationship between music and speech rhythm is more widespread than previously thought and that musical rhythm production by amateurs and novices is concordant with their rhythmic expectations in the perception of speech.

Losing the beat: deficits in temporal coordination.

Tapping or clapping to an auditory beat, an easy task for most individuals, reveals precise temporal synchronization with auditory patterns such as music, even in the presence of temporal fluctuations. Most models of beat-tracking rely on the theoretical concept of pulse: a perceived regular beat generated by an internal oscillation that forms the foundation of entrainment abilities. Although tapping to the beat is a natural sensorimotor activity for most individuals, not everyone can track an auditory beat. Recently, the case of Mathieu was documented (Phillips-Silver et al. 2011 Neuropsychologia 49, 961-969. (doi:10.1016/j.neuropsychologia.2011.02.002)). Mathieu presented himself as having difficulty following a beat and exhibited synchronization failures. We examined beat-tracking in normal control participants, Mathieu, and a second beat-deaf individual, who tapped with an auditory metronome in which unpredictable perturbations were introduced to disrupt entrainment. Both beat-deaf cases exhibited failures in error correction in response to the perturbation task while exhibiting normal spontaneous motor tempi (in the absence of an auditory stimulus), supporting a deficit specific to perception-action coupling. A damped harmonic oscillator model was applied to the temporal adaptation responses; the model's parameters of relaxation time and endogenous frequency accounted for differences between the beat-deaf cases as well as the control group individuals.

Successful measurement of the mismatch negativity despite a concurrent movie soundtrack: reduced amplitude but normal component morphology.

OBJECTIVE: To examine the mechanisms responsible for the reduction of the mismatch negativity (MMN) ERP component observed in response to pitch changes when the soundtrack of a movie is presented while recording the MMN. METHODS: In three experiments we measured the MMN to tones that differed in pitch from a repeated standard tone presented with a silent subtitled movie, with the soundtrack played forward or backward, or with soundtracks set at different intensity levels. RESULTS: MMN amplitude was reduced when the soundtrack was presented either forward or backward compared to the silent subtitled movie. With the soundtrack, MMN amplitude increased proportionally to the increments in the sound-to-noise intensity ratio. CONCLUSION: MMN was reduced in amplitude but had normal morphology with a concurrent soundtrack, most likely because of basic acoustical interference from the soundtrack with MMN-critical tones rather than from attentional effects. SIGNIFICANCE: A normal MMN can be recorded with a concurrent movie soundtrack, but signal amplitudes need to be set with caution to ensure a sufficiently high sound-to-noise ratio between MMN stimuli and the soundtrack.

Listeners feel the beat: entrainment to English and French speech rhythms.

Can listeners entrain to speech rhythms? Monolingual speakers of English and French and balanced English-French bilinguals tapped along with the beat they perceived in sentences spoken in a stress-timed language, English, and a syllable-timed language, French. All groups of participants tapped more regularly to English than to French utterances. Tapping performance was also influenced by the participants' native language: English-speaking participants and bilinguals tapped more regularly and at higher metrical levels than did French-speaking participants, suggesting that long-term linguistic experience with a stress-timed language can differentiate speakers' entrainment to speech rhythm.

Early integration of vowel and pitch processing: a mismatch negativity study.

OBJECTIVE: Several studies have explored the processing specificity of music and speech, but only a few have addressed the processing autonomy of their fundamental components: pitch and phonemes. Here, we examined the additivity of the mismatch negativity (MMN) indexing the early interactions between vowels and pitch when sung. METHODS: Event-related potentials (ERPs) were recorded while participants heard frequent sung vowels and rare stimuli deviating in pitch only, in vowel only, or in both pitch and vowel. The task was to watch a silent movie while ignoring the sounds. RESULTS: All three types of deviants elicited both an MMN and a P3a ERP component. The observed MMNs were of similar amplitude for the three types of deviants and the P3a was larger for double deviants. The MMNs to deviance in vowel and deviance in pitch were not additive. CONCLUSIONS: The underadditivity of the MMN responses suggests that vowel and pitch differences are processed by interacting neural networks. SIGNIFICANCE: The results indicate that vowel and pitch are processed as integrated units, even at a pre-attentive level. Music-processing specificity thus rests on more complex dimensions of music and speech.

Integrated preattentive processing of vowel and pitch: a mismatch negativity study.

This study examines the additivity of the Mismatch Negativity (MMN) as an index of the early interactions between vowels and pitch when sung. Event-related potentials (ERPs) were recorded while participants were presented with sung vowels. Sixteen percent of stimuli deviated in pitch only, in vowel only, or in both pitch and vowel. All three kinds of deviants elicited an MMN of similar amplitude. The MMNs to vowel and pitch deviants did not show significant additivity. This suggests that vowel and pitch are processed by shared neural substrates at the preattentive level.

Processing interactions between phonology and melody: vowels sing but consonants speak.

The aim of this study was to determine if two dimensions of song, the phonological part of lyrics and the melodic part of tunes, are processed in an independent or integrated way. In a series of five experiments, musically untrained participants classified bi-syllabic nonwords sung on two-tone melodic intervals. Their response had to be based on pitch contour, on nonword identity, or on the combination of pitch and nonword. When participants had to ignore irrelevant variations of the non-attended dimension, patterns of interference and facilitation allowed us to specify the processing interactions between dimensions. Results showed that consonants are processed more independently from melodic information than vowels are (Experiments 1-4). This difference between consonants and vowels was neither related to the sonority of the phoneme (Experiment 3), nor to the acoustical correlates between vowel quality and pitch height (Experiment 5). The implication of these results for our understanding of the functional relationships between musical and linguistic systems is discussed in light of the different evolutionary origins and linguistic functions of consonants and vowels.

Spatial associations for musical stimuli: a piano in the head?

This study was aimed at examining whether pitch height and pitch change are mentally represented along spatial axes. A series of experiments explored, for isolated tones and 2-note intervals, the occurrence of effects analogous to the spatial numerical association of response codes (SNARC) effect. Response device orientation (horizontal vs. vertical), task, and musical expertise of the participants were manipulated. The pitch of isolated tones triggered the automatic activation of a vertical axis independently of musical expertise, but the contour of melodic intervals did not. By contrast, automatic associations with the horizontal axis seemed linked to music training for pitch and, to a lower extent, for intervals. These results, discussed in the light of studies on number representation, provide a new example of the effects of musical expertise on music cognition.