Interactive effects of linguistic abstraction and stimulus statistics in the online modulation of neural speech encoding

Abstract

Speech processing is highly modulated by context. Prior studies examining frequency-following responses (FFRs), an electrophysiological 'neurophonic' potential that faithfully reflects phase-locked activity from neural ensembles within the auditory network, have demonstrated that stimulus context modulates the integrity of speech encoding. The extent to which context-dependent encoding reflects general auditory properties or interactivities between statistical and higher-level linguistic processes remains unexplored. Our study examined whether speech encoding, as reflected by FFRs, is modulated by abstract phonological relationships between a stimulus and surrounding contexts. FFRs were elicited to a Mandarin rising-tone syllable (/ji-TR/, 'second') randomly presented with other syllables in three contexts from 17 native listeners. In a contrastive context, /ji-TR/ occurred with meaning-contrastive high-level-tone syllables (/ji-H/, 'one'). In an allotone context, TR occurred with dipping-tone syllables /ji-D/, a non-meaning-contrastive variant of /ji-TR/. In a repetitive context, the same /ji-TR/ occurred with other speech tokens of /ji-TR/. Consistent with prior work, neural tracking of /ji-TR/ pitch contour was more faithful in the repetitive condition wherein /ji-TR/ occurred more predictably (p = 1) than in the contrastive condition (p = 0.34). Crucially, in the allotone context, neural tracking of /ji-TR/ was more accurate relative to the contrastive context, despite both having an identical transitional probability (p = 0.34). Mechanistically, the non-meaning-contrastive relationship may have augmented the probability to /ji-TR/ occurrence in the allotone context. Results indicate online interactions between bottom-up and top-down mechanisms, which facilitate speech perception. Such interactivities may predictively fine-tune incoming speech encoding using linguistic and statistical information from prior context.

Frequency-Following Responses to Speech Sounds Are Highly Conserved across Species and Contain Cortical Contributions

“…The syllable /yi/ with four different pitch patterns (tones) were used to elicit the FFRs. These pitch patterns are linguistically relevant in Mandarin and have been extensively used to examine experience-dependent auditory plasticity ( Krishnan et al, 2010a , 2012 ; Lau et al, 2017 , 2019 ; Llanos et al, 2017 ; Reetzke et al, 2018 ). The minimally contrastive F0 patterns are phonetically described as T1 (high-level, F0 = 129 Hz), T2 (low-rising, F0 ranging from 109 to 133 Hz), T3 (low-dipping, F0 ranging from 89 to 111 Hz), and T4 (high-falling, F0 ranging from 140 to 92 Hz).…”

Deconstructing the Cortical Sources of Frequency Following Responses to Speech: A Cross-species Approach

“…These pitch patterns are linguistically-relevant in Mandarin and have been extensively used to examine experience-dependent auditory plasticity (Krishnan et al, 2010b(Krishnan et al, , 2012Lau et al, 2017Lau et al, , 2018Llanos et al, 2017;Reetzke et al, 2018). The minimally contrastive F0 patterns are phonetically described as T1 (high-level, F0 = 129 Hz), T2 (low-rising, F0 ranging from 109 to 133 Hz), T3 (low-dipping, F0 ranging from 89 to 111 Hz), and T4 (high-falling, F0 ranging from 140 to 92 Hz).…”

“…We used four-pitch variants of the vowel /yi/ (Fig 1B ), referred to as Mandarin tones to elicit the FFRs (Fig 1C). These Mandarin tones have been extensively used to record FFRs to study the neurophysiology of pitch processing and associated plasticity in humans (Krishnan et al, 2010a;Llanos et al, 2017;Lau et al, 2018;Reetzke et al, 2018). The Mandarin tones are phonetically described as; T1 (high-level F0), T2 (low-rising F0), T3 (low-dipping F0), and T4 (high-falling F0).…”

“…We harmonized EEG recording procedures and elicited robust FFRs to timevarying pitch patterns across species. Cross-species translation is facilitated by using identical (and unfamiliar) speech stimuli (Mandarin tone patterns) that have extensively been used in prior work to elicit the FFR (49)(50)(51)(52)(53)(54). Representational similarity analysis (RSA) served as a translational bridge (55,56), allowing us to quantify similarities in pitch encoding across species despite inherent fundamental anatomical differences and arousal states.…”

“…We further demonstrate, using layerspecific FFR recordings, that neurons in the thalamorecipient layers of the primary auditory cortex We used four-pitch variants of the vowel /yi/ (Fig 1B ), referred to as Mandarin tones to elicit the FFRs (Fig 1C). Mandarin tones have been extensively used to record FFRs to study the neurophysiology of pitch processing and associated plasticity in humans (50,52,53,58). The Mandarin tones are phonetically described as; T1 (high-level F0), T2 (low-rising F0), T3 (lowdipping F0), and T4 (high-falling F0).…”