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

Abstract

It has been demonstrated that neural encoding of pitch in the auditory brainstem is shaped by longterm 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 in order 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 pitchtracking 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.

Language-experience plasticity in neural representation of changes in pitch salience

“…The increase in pitch relevant neural activity in the FFR suggests that an increase in the neural periodicity strength results from increasing temporal regularity of the stimulus (Krishnan et al, 2010a; Krishnan et al, 2010b). This interpretation is consistent with perceptual (Patterson et al, 1996; Yost, 1996a) and physiologic (Sayles and Winter, 2007; Shofner, 1999) data indicating that the pitch of static and dynamic IRN stimuli is based on an autocorrelation-like temporal processing.…”

“…Of special relevance to this study, FFR neural periodicity strength increases with increasing pitch salience and accurately predicts the perceptual salience of IRN pitch (Krishnan et al, 2010a). FFRs further reveal that experience-dependent brainstem mechanisms for pitch are especially sensitive to those attributes of pitch contours that provide cues of high perceptual saliency in degraded as well as normal listening conditions (Krishnan et al, 2010b). …”

Investigation of auditory processing disorder and language impairment using the speech-evoked auditory brainstem response

“…Several studies of the brainstem encoding of speech sounds have been conducted in native English, Arabic, Hebrew, and Chinese speakers (Russo et al, 2004a;Karawani and Banai, 2010;Krishnan et al, 2010). As a consequence of the specific characteristics of acoustic signals that are maintained and reflected with remarkable precision in the subcortical pathway, those studies were able to provide direct information on how speech syllables are neuronally encoded by the auditory system (Chandrasekaran and Kraus, 2010;Johnson et al, 2005Johnson et al, , 2008Russo et al, 2004).…”

Experience-dependent enhancement of pitch-specific responses in the auditory cortex is limited to acceleration rates in normal voice range

“…This heightened sensitivity to sections characterized by rapid changes in pitch is maintained even in severely degraded stimuli (Krishnan et al, 2010a). Particularly relevant here are our previous results (Krishnan et al, 2010b) that exhibit more robust brainstem representation of pitch relevant information in Chinese listeners, relative to English, across a four-step acceleration rate continuum where the lowest rate was equivalent to Mandarin Tone 2 (T2) and the fastest rate fell well outside the normal range of dynamic pitch.…”