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

Abstract

Neural representation of pitch-relevant information at the brainstem and cortical levels of processing is influenced by language experience. A well-known attribute of pitch is its salience. Brainstem frequency following responses and cortical pitch specific responses, recorded concurrently, were elicited by a pitch salience continuum spanning weak to strong pitch of a dynamic, iterated rippled noise pitch contour—homolog of a Mandarin tone. Our aims were to assess how language experience (Chinese, English) affects i) enhancement of neural activity associated with pitch salience at brainstem and cortical levels, ii) the presence of asymmetry in cortical pitch representation, and iii) patterns of relative changes in magnitude along the pitch salience continuum. Peak latency (Fz: Na, Pb, Nb) was shorter in the Chinese than the English group across the continuum. Peak-to-peak amplitude (Fz: Na-Pb, Pb-Nb) of the Chinese group grew larger with increasing pitch salience, but an experience-dependent advantage was limited to the Na-Pb component. At temporal sites (T7/T8), the larger amplitude of the Chinese group across the continuum was both limited to the Na-Pb component and the right temporal site. At the brainstem level, F0 magnitude gets larger as you increase pitch salience, and it too reveals Chinese superiority. A direct comparison of cortical and brainstem responses for the Chinese group reveals different patterns of relative changes in magnitude along the pitch salience continuum. Such differences may point to a transformation in pitch processing at the cortical level presumably mediated by local sensory and/or extrasensory influence overlaid on the brainstem output.

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

“…This finding for Na–Pb in Quiet is consistent with previous studies showing experience-dependent enhancement of CPR components with manipulation of several different temporal attributes of pitch (Krishnan et al, 2014a; Krishnan et al, 2015a; Krishnan et al, 2015b; Krishnan et al, 2016; Krishnan et al, 2017b). Despite the presence of noise (+5 dB SNR), cortical pitch mechanisms shaped by experience are more stable and relatively less susceptible to degradative effects of noise.…”

“…Such enhancement in both Quiet and noise is likely mediated by selective recruitment of neural elements with sharper tuning, greater temporal synchronization, and improved synaptic efficiency. 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 (for additional discussion, see Krishnan et al, 2016, p. 111). These adaptive, cortical pitch mechanisms not only serve to sharpen neural response properties to optimize representation of temporal attributes of pitch in Quiet, but more importantly, are more resilient to degradation in adverse listening conditions that present a reduced SNR.…”

“…Both temporal and spectral cues for pitch are likely degraded by the background noise. Besides background noise, other manipulations of pitch stimuli that degrade SNR have also resulted in smaller CPR amplitude changes; e.g., weak pitch salience (Krishnan et al, 2016; Krishnan et al, 2012b); rapid pitch acceleration (Krishnan et al, 2015a). These degradative effects of background noise are already evident in subcortical representation of other acoustic stimuli (Bidelman & Krishnan, 2010; Bidelman & Howell, 2016; Parbery-Clark et al, 2009a).…”

“…There is indirect evidence to suggest that experience-dependent pitch representations at cortical and subcortical levels are relatively more resistant to stimulus degradation (rapid pitch change: Krishnan et al, 2015a; reduced pitch salience: Krishnan et al, 2016). 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, 2009a; higher harmonics only) and reverberation (Bidelman & Krishnan, 2010).…”

Complementary metrics of human auditory nerve function derived from compound action potentials

“…However, these responses are generated at the level of the brainstem and individual 410 differences in both central and AN function could contribute to the response. This limitation is of 411 particular importance when examining different experimental or patient populations, as both age 412 and experience are known to affect central neural function (Clinard and Tremblay 2013;Clinard 413 et al 2010;Krishnan et al 2016;Wong et al 2007). Therefore, changes observed in these 414 responses could be a consequence of a combination of AN and central factors.…”