Language experience enhances early cortical pitch-dependent responses

AbstractPitch processing at cortical and subcortical stages of processing is shaped by language experience. We recently demonstrated that specific components of the cortical pitch response (CPR) index the more rapidly-changing portions of the high rising Tone 2 of Mandarin Chinese, in addition to marking pitch onset and sound offset. In this study, we examine how language experience (Mandarin vs. English) shapes the processing of different temporal attributes of pitch reflected in the CPR components using stimuli representative of within-category variants of Tone 2. Results showed that the magnitude of CPR components (Na–Pb and Pb–Nb) and the correlation between these two components and pitch acceleration were stronger for the Chinese listeners compared to English listeners for stimuli that fell within the range of Tone 2 citation forms. Discriminant function analysis revealed that the Na–Pb component was more than twice as important as Pb–Nb in grouping listeners by language affiliation. In addition, a stronger stimulus-dependent, rightward asymmetry was observed for the Chinese group at the temporal, but not frontal, electrode sites. This finding may reflect selective recruitment of experience-dependent, pitch-specific mechanisms in right auditory cortex to extract more complex, time-varying pitch patterns. Taken together, these findings suggest that long-term language experience shapes early sensory level processing of pitch in the auditory cortex, and that the sensitivity of the CPR may vary depending on the relative linguistic importance of specific temporal attributes of dynamic pitch

Phase locked neural activity in the human brainstem predicts preference for musical consonance.

When musical notes are combined to make a chord, the closeness of fit of the combined spectrum to a single harmonic series (the 'harmonicity' of the chord) predicts the perceived consonance (how pleasant and stable the chord sounds; McDermott, Lehr, & Oxenham, 2010). The distinction between consonance and dissonance is central to Western musical form. Harmonicity is represented in the temporal firing patterns of populations of brainstem neurons. The current study investigates the role of brainstem temporal coding of harmonicity in the perception of consonance. Individual preference for consonant over dissonant chords was measured using a rating scale for pairs of simultaneous notes. In order to investigate the effects of cochlear interactions, notes were presented in two ways: both notes to both ears or each note to different ears. The electrophysiological frequency following response (FFR), reflecting sustained neural activity in the brainstem synchronised to the stimulus, was also measured. When both notes were presented to both ears the perceptual distinction between consonant and dissonant chords was stronger than when the notes were presented to different ears. In the condition in which both notes were presented to the both ears additional low-frequency components, corresponding to difference tones resulting from nonlinear cochlear processing, were observable in the FFR effectively enhancing the neural harmonicity of consonant chords but not dissonant chords. Suppressing the cochlear envelope component of the FFR also suppressed the additional frequency components. This suggests that, in the case of consonant chords, difference tones generated by interactions between notes in the cochlea enhance the perception of consonance. Furthermore, individuals with a greater distinction between consonant and dissonant chords in the FFR to individual harmonics had a stronger preference for consonant over dissonant chords. Overall, the results provide compelling evidence for the role of neural temporal coding in the perception of consonance, and suggest that the representation of harmonicity in phase locked neural firing drives the perception of consonance

Effects of reverberation on brainstem representation of speech in musicians and non-musicians

Perceptual and neurophysiological enhancements in linguistic processing in musicians suggest that domain specific experience may enhance neural resources recruited for language specific behaviors. In everyday situations, listeners are faced with extracting speech signals in degraded listening conditions. Here, we examine whether musical training provides resilience to the degradative effects of reverberation on subcortical representations of pitch and formant-related harmonic information of speech. Brainstem frequency-following responses (FFRs) were recorded from musicians and non-musician controls in response to the vowel /i/ in four different levels of reverberation and analyzed based on their spectro-temporal composition. For both groups, reverberation had little effect on the neural encoding of pitch but significantly degraded neural encoding of formant-related harmonics (i.e., vowel quality) suggesting a differential impact on the source-filter components of speech. However, in quiet and across nearly all reverberation conditions, musicians showed more robust responses than non-musicians. Neurophysiologic results were confirmed behaviorally by comparing brainstem spectral magnitudes with perceptual measures of fundamental (F0) and first formant (F1) frequency difference limens (DLs). For both types of discrimination, musicians obtained DLs which were 2-4 times better than non-musicians. Results suggest that musicians\u27 enhanced neural encoding of acoustic features, an experience-dependent effect, is more resistant to reverberation degradation which may explain their enhanced perceptual ability on behaviorally relevant speech and/or music tasks in adverse listening conditions. © 2010 Elsevier B.V. All rights reserved

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. Copyright © 2009 Society for Neuroscience

Auditory brainstem correlates of basilar membrane nonlinearity in humans

A behavioral measure of the basilar membrane response can be obtained by comparing the growth in forward masking for maskers at, and well below, the signal frequency. Since the off-frequency masker is assumed to be processed linearly at the signal place, the difference in masking growth with level is thought to reflect the compressive response to the on-frequency masker. The present experiment used an electrophysiological analog of this technique, based on measurements of the latency of wave V of the auditory brain-stem response elicited by a 4-kHz, 4-ms pure tone, presented at 65 dB SPL. Responses were obtained in quiet and in the presence of either an on-frequency (4 kHz) or an off-frequency (1.8 kHz) pure-tone forward masker. Wave V latency increased with masker level, although the increase was greater for the off-frequency masker than for the on-frequency masker, consistent with a more compressive response to the latter. Response functions generated from the data showed the characteristic shape, with a nearly linear response at lower levels and 4: 1 compression at higher levels. However, the breakpoint between the linear region and the compressive region was at about 60 dB SPL, higher than expected on the basis of previous physiological and psychophysical measures

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 \u3eminor \u3e\u3ediminished \u3eaugmented). Moreover, neural response magnitudes showed high correspondence with listeners\u27 perceptual ratings of the same chords. Results suggest that preattentive stages of pitch processing may contribute to perceptual judgments of musical harmony. © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins

Neural encoding in the human brainstem relevant to the pitch of complex tones

Psychoacoustic studies have shown that complex tones containing resolved harmonics evoke stronger pitches than complex tones with only unresolved harmonics. Also, unresolved harmonics presented in alternating sine and cosine (ALT) phase produce a doubling of pitch. We examine here whether the temporal pattern of phase-locked neural activity reflected in the scalp recorded human frequency following response (FFR) preserves information relevant to pitch strength, and to the doubling of pitch for ALT stimuli. Results revealed stronger neural periodicity strength for resolved stimuli, although the effect of resolvability was weak compared to the effect observed behaviorally; autocorrelation functions and FFR spectra suggest a different pattern of phase-locked neural activity for ALT stimuli with resolved and unresolved harmonics consistent with the doubling of pitch observed in our behavioral estimates; and the temporal pattern of neural activity underlying pitch encoding appears to be similar at the auditory nerve (auditory nerve model response) and the rostral brainstem level (FFR). These findings suggest that the phase-locked neural activity reflected in the scalp recorded FFR preserves neural information relevant to pitch that could serve as an electrophysiological correlate of the behavioral pitch measure. The scalp recorded FFR may provide for a non-invasive analytic tool to evaluate neural encoding of complex sounds in humans