Language experience-dependent advantage in pitch representation in the auditory cortex is limited to favorable signal-to-noise ratios

Abstract

Long-term experience enhances neural representation of temporal attributes of pitch in the brainstem and auditory cortex in favorable listening conditions. Herein we examine whether cortical pitch mechanisms shaped by language experience are more resilient to degradation in background noise, and exhibit greater binaural release from masking (BRM). Cortical pitch responses (CPR) were recorded from Mandarin- and English-speaking natives using a Mandarin word exhibiting a high rising pitch (/yi2/). Stimuli were presented diotically in Quiet, and in noise at +5, and 0 dB SNR. CPRs were also recorded in binaural conditions, SONO (where signal and noise were in phase at both ears); or S0Nπ (where signal was in phase and noise 180 degrees out of phase at each ear), using 0 dB SNR. At Fz, both groups showed increase in CPR peak latency and decrease in amplitude with increasing noise level. A language-dependent enhancement of Na–Pb amplitude (Chinese > English) was restricted to Quiet and +5 dB SNR conditions. At T7/T8 electrode sites, Chinese natives exhibited a rightward asymmetry for both CPR components. A language-dependent effect (Chinese > English) was restricted to T8. Regarding BRM, both CPR components showed greater response amplitude for the S0Nπ condition compared to S0N0 across groups. Rightward asymmetry for BRM in the Chinese group indicates experience-dependent recruitment of right auditory cortex. Restriction of the advantage in pitch representation to the quiet and +5 SNR conditions, and the absence of group differences in the binaural release from masking, suggest that language experience affords limited advantage in the neural representation of pitch-relevant information in the auditory cortex under adverse listening conditions.

Tone language experience-dependent advantage in pitch representation in brainstem and auditory cortex is maintained under reverberation

“…This suggests that long-term experience shapes pitch mechanisms in order to preserve a gain in signal-to-noise ratio in the presence of reverberation. Such findings add to the extant literature on experience-dependent, compensatory adjustment to deleterious effects of adverse listening conditions on both subcortical and cortical representation of complex sounds (Bidelman, 2018;Bidelman et al, 2018;Krishnan et al, 2010a;Parbery-Clark et al, 2009;Suresh et al, 2017).…”

“…Pb-Nb may be more susceptible to reverberation-induced degradation compared to a temporal window indexing the earlier slow-acceleration segment of the pitch contour (Na-Pb). Consistent with this view, the later integration window (Pb-Nb) has also been shown to be more susceptible to noise degradation (Suresh et al, 2017).…”

“…In our view, the Chinese group's enhancement represents modulation of early sensory pitch mechanisms in the brainstem and auditory cortex that interact with extrasensory processes at a higher hierarchical level in the auditory cortex (see also Krishnan et al, 2016, p. 111). Such adaptive pitch mechanisms are also essential to sharpen neural response properties to optimally capture temporal attributes of pitch in reduced SNR conditions (Suresh et al, 2017).…”

“…As such, they provide physiologic windows to evaluate the hierarchical organization of pitch processing along the auditory pathway. FFR reflects sustained phase-locked neural activity in a population of neural elements primarily within the rostral brainstem (Chandrasekaran & Kraus, 2010;Krishnan, 2007;Suresh et al, 2017). Pitch-relevant neural activity preserved in the FFR is strongly correlated with behavioral measures of pitch (Bidelman & Krishnan, 2010;Krishnan & Plack, 2009;Krishnan et al, 2010b;Parbery-Clark et al, 2009).…”

“…Neuroanatomic (Saldana et al, 1996) and physiologic evidence (Suga et al, 2003) support enhanced neural representation in subcortical structures mediated by corticofugal pathways suggesting a well-coordinated interplay between brainstem and cortical processes mediating pitch processing. There is indirect evidence to suggest that experience-dependent pitch representations at cortical and subcortical levels are relatively more resistant to stimulus degradation; for example, rapid pitch change (Krishnan et al, 2015a), reduced pitch salience (Krishnan et al, 2016), and background noise (Suresh et al, 2017). Similarly, brainstem neural representation of voice fundamental frequency (F0) and the first formant frequency (F1) in musicians show greater resilience to degradative effects of noise (Parbery-Clark et al, 2009) and reverberation (Bidelman & Krishnan, 2010).…”