Neural Encoding Of Pitch Research Articles

Lifelong Tone Language Experience does not Eliminate Deficits in Neural Encoding of Pitch in Autism Spectrum Disorder.

Atypical pitch processing is a feature of Autism Spectrum Disorder (ASD), which affects non-tone language speakers' communication. Lifelong auditory experience has been demonstrated to modify genetically-predisposed risks for pitch processing. We examined individuals with ASD to test the hypothesis that lifelong auditory experience in tone language mayeliminate impaired pitch processing in ASD. We examined children's and adults' Frequency-following Response (FFR), a neurophysiological component indexing early neural sensory encoding of pitch. Univariate and machine-learning-based analytics suggest less robust pitch encoding and diminished pitch distinctions in the FFR from individuals with ASD. Contrary to our hypothesis, results point to a linguistic pitch encoding impairment associated with ASD that may not be eliminated even by lifelong sensory experience.

ERP correlates of pitch error detection in complex Tone and Voice auditory feedback with missing fundamental

Previous studies have shown that the pitch of a sound is perceived in the absence of its fundamental frequency (F0), suggesting that a distinct mechanism may resolve pitch based on a pattern that exists between harmonic frequencies. The present study investigated whether such a mechanism is active during voice pitch control. ERPs were recorded in response to +200 cents pitch shifts in the auditory feedback of self-vocalizations and complex tones with and without the F0. The absence of the fundamental induced no difference in ERP latencies. However, a right-hemisphere difference was found in the N1 amplitudes with larger responses to complex tones that included the fundamental compared to when it was missing. The P1 and N1 latencies were shorter in the left hemisphere, and the N1 and P2 amplitudes were larger bilaterally for pitch shifts in voice and complex tones compared with pure tones. These findings suggest hemispheric differences in neural encoding of pitch in sounds with missing fundamental. Data from the present study suggest that the right cortical auditory areas, thought to be specialized for spectral processing, may utilize different mechanisms to resolve pitch in sounds with missing fundamental. The left hemisphere seems to perform faster processing to resolve pitch based on the rate of temporal variations in complex sounds compared with pure tones. These effects indicate that the differential neural processing of pitch in the left and right hemispheres may enable the audio-vocal system to detect temporal and spectral variations in the auditory feedback for vocal pitch control.

Neural Encoding of Speech and Music: Implications for Hearing Speech in Noise.

Understanding speech in a background of competing noise is challenging, especially for individuals with hearing loss or deficits in auditory processing ability. The ability to hear in background noise cannot be predicted from the audiogram, an assessment of peripheral hearing ability; therefore, it is important to consider the impact of central and cognitive factors on speech-in-noise perception. Auditory processing in complex environments is reflected in neural encoding of pitch, timing, and timbre, the crucial elements of speech and music. Musical expertise in processing pitch, timing, and timbre may transfer to enhancements in speech-in-noise perception due to shared neural pathways for speech and music. Through cognitive-sensory interactions, musicians develop skills enabling them to selectively listen to relevant signals embedded in a network of melodies and harmonies, and this experience leads in turn to enhanced ability to focus on one voice in a background of other voices. Here we review recent work examining the biological mechanisms of speech and music perception and the potential for musical experience to ameliorate speech-in-noise listening difficulties.

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' 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.

Brainstem pitch representation in native speakers of Mandarin is less susceptible to degradation of stimulus temporal regularity

It has been demonstrated that neural encoding of pitch in the auditory brainstem is shaped by long-term experience with language. To date, however, all stimuli have exhibited a high degree of pitch saliency. The experimental design herein permits us to determine whether experience-dependent pitch representation in the brainstem is less susceptible to progressive degradation of the temporal regularity of iterated rippled noise (IRN). Brainstem responses were recorded from Chinese and English participants in response to IRN homologues of Mandarin Tone 2 (T2 IRN). Six different iterations steps were utilized to systematically vary the degree of temporal regularity in the fine structure of the IRN stimuli to produce a pitch salience continuum ranging from low to high. Pitch-tracking accuracy and pitch strength were computed from the brainstem responses using autocorrelation algorithms. Analysis of variance of brainstem responses to T2 IRN revealed that pitch-tracking accuracy is higher in the native tone language group (Chinese) relative to the non-tone language group (English) except for the three lowest steps along the continuum, and moreover, that pitch strength is greater in the Chinese group even in severely degraded stimuli for two of the six 40-ms sections of T2 IRN that exhibit rapid changes in pitch. For these same two sections, exponential time constants for the stimulus continuum revealed that pitch strength emerges 2–3 times faster in the tone language than in the non-tone language group as a function of increasing pitch salience. These findings altogether suggest that experience-dependent brainstem mechanisms for pitch are especially sensitive to those dimensions of tonal contours that provide cues of high perceptual saliency in degraded as well as normal listening conditions.

The effects of tone language experience on pitch processing in the brainstem

Neural encoding of pitch in the auditory brainstem is shaped by long-term experience with language. The aim herein was to determine to what extent this experience-dependent effect is specific to a particular language. Analysis of variance of brainstem responses to Mandarin and Thai tones revealed that regardless of language identity, pitch-tracking accuracy of whole tones was higher in the two tone language groups (Chinese, Thai) compared to the non-tone language group (English), and that pitch strength of 40-ms tonal sections was generally more robust in tone relative to non-tone languages. Discriminant analysis of tonal sections, as defined by variation in direction and degree of slope, showed that moderate rising pitch was the most important variable for classifying English, Chinese, and Thai participants into their respective groups. We conclude that language-dependent enhancement of pitch representation transfers to other languages with similar phonological systems. From a neurobiological perspective, these findings suggest that neural mechanisms local to the brainstem are tuned for processing pitch dimensions that are perceptually salient depending upon the melodic patterns of a language.

Interdependent encoding of pitch, timbre, and spatial location in auditory cortex.

Because we can perceive the pitch, timbre, and spatial location of a sound source independently, it seems natural to suppose that cortical processing of sounds might separate out spatial from nonspatial attributes. Indeed, recent studies support the existence of anatomically segregated "what" and "where" cortical processing streams. However, few attempts have been made to measure the responses of individual neurons in different cortical fields to sounds that vary simultaneously across spatial and nonspatial dimensions. We recorded responses to artificial vowels presented in virtual acoustic space to investigate the representations of pitch, timbre, and sound source azimuth in both core and belt areas of ferret auditory cortex. A variance decomposition technique was used to quantify the way in which altering each parameter changed neural responses. Most units were sensitive to two or more of these stimulus attributes. Although indicating that neural encoding of pitch, location, and timbre cues is distributed across auditory cortex, significant differences in average neuronal sensitivity were observed across cortical areas and depths, which could form the basis for the segregation of spatial and nonspatial cues at higher cortical levels. Some units exhibited significant nonlinear interactions between particular combinations of pitch, timbre, and azimuth. These interactions were most pronounced for pitch and timbre and were less commonly observed between spatial and nonspatial attributes. Such nonlinearities were most prevalent in primary auditory cortex, although they tended to be small compared with stimulus main effects.