A neurophysiological study into the foundations of tonal harmony

Relationship between early neural responses to syntactic and acoustic irregularities in music

Humans can detect various anomalies in a sound sequence without attending to each dimension explicitly. Event-related potentials (ERPs) have been used to examine the processes of auditory deviance detection. Previous research has shown that music-syntactic anomalies elicit early right anterior negativity (ERAN), whereas more general acoustic irregularities elicit mismatch negativity (MMN). Although these ERP components occur in a similar latency range with a similar scalp topography, the relationship between the detection processes they reflect remains unclear. This study compared these components by manipulating music-syntactic (chord progression) and acoustic (intensity) irregularities orthogonally in two experiments. Non-musicians (Experiment 1: N = 39; Experiment 2: N = 24) were asked to listen to chord sequences, each consisting of 5 four-voice chords, as they watched a silent video clip. Standard, harmonic-deviant, intensity-deviant and double-deviant chords occurred at the final position in each sequence. Deviant stimuli were presented infrequently (p = .10) in Experiment 1 and equiprobably (p = .25) in Experiment 2. Regardless of deviance probability, both harmonic and intensity deviants elicited similar negativities, which were indistinguishable in terms of latency or scalp distribution. When the two deviant types occurred simultaneously, the negativity increased in an additive manner; that is, the amplitude of the double-deviant ERP was as large as the sum of the single-deviant ERPs. These findings suggest that the detection of music-syntactic and acoustic irregularities works independently, based on different regularity representations.

Asymmetries in the processing of vowel height

PURPOSE

Speech perception can be described as the transformation of continuous acoustic information into discrete memory representations. Therefore, research on neural representations of speech sounds is particularly important for a better understanding of this transformation. Speech perception models make specific assumptions regarding the representation of mid vowels (e.g., [ε]) that are articulated with a neutral position in regard to height. One hypothesis is that their representation is less specific than the representation of vowels with a more specific position (e.g., [æ]).

METHOD

In a magnetoencephalography study, we tested the underspecification of mid vowel in American English. Using a mismatch negativity (MMN) paradigm, mid and low lax vowels ([ε]/[æ]), and high and low lax vowels ([i]/[æ]), were opposed, and M100/N1 dipole source parameters as well as MMN latency and amplitude were examined.

RESULTS

Larger MMNs occurred when the mid vowel [ε] was a deviant to the standard [æ], a result consistent with less specific representations for mid vowels. MMNs of equal magnitude were elicited in the high-low comparison, consistent with more specific representations for both high and low vowels. M100 dipole locations support early vowel categorization on the basis of linguistically relevant acoustic-phonetic features.

CONCLUSION

We take our results to reflect an abstract long-term representation of vowels that do not include redundant specifications at very early stages of processing the speech signal. Moreover, the dipole locations indicate extraction of distinctive features and their mapping onto representationally faithful cortical locations (i.e., a feature map).

Brainstem correlates of behavioral and compositional preferences of musical harmony

Certain chords are preferred by listeners behaviorally and also occur with higher regularity in musical composition. Event-related potentials index the perceived consonance (i.e., pleasantness) of musical pitch relationships providing a cortical neural correlate for such behavioral preferences. Here, we show correlates of these harmonic preferences exist at subcortical stages of audition. Brainstem frequency-following responses were measured in response to four prototypical musical triads. Pitch salience computed from frequency-following responses correctly predicted the ordering of triadic harmony stipulated by music theory (i.e., major >minor >>diminished >augmented). Moreover, neural response magnitudes showed high correspondence with listeners' perceptual ratings of the same chords. Results suggest that preattentive stages of pitch processing may contribute to perceptual judgments of musical harmony.

Neural correlates of consonance, dissonance, and the hierarchy of musical pitch in the human brainstem

Consonant and dissonant pitch relationships in music provide the foundation of melody and harmony, the building blocks of Western tonal music. We hypothesized that phase-locked neural activity within the brainstem may preserve information relevant to these important perceptual attributes of music. To this end, we measured brainstem frequency-following responses (FFRs) from nonmusicians in response to the dichotic presentation of nine musical intervals that varied in their degree of consonance and dissonance. Neural pitch salience was computed for each response using temporally based autocorrelation and harmonic pitch sieve analyses. Brainstem responses to consonant intervals were more robust and yielded stronger pitch salience than those to dissonant intervals. In addition, the ordering of neural pitch salience across musical intervals followed the hierarchical arrangement of pitch stipulated by Western music theory. Finally, pitch salience derived from neural data showed high correspondence with behavioral consonance judgments (r = 0.81). These results suggest that brainstem neural mechanisms mediating pitch processing show preferential encoding of consonant musical relationships and, furthermore, preserve the hierarchical pitch relationships found in music, even for individuals without formal musical training. We infer that the basic pitch relationships governing music may be rooted in low-level sensory processing and that an encoding scheme that favors consonant pitch relationships may be one reason why such intervals are preferred behaviorally.