Neural Correlates of Early Sound Encoding and their Relationship to Speech-in-Noise Perception

Abstract

Speech-in-noise (SIN) perception is a complex cognitive skill that affects social, vocational, and educational activities. Poor SIN ability particularly affects young and elderly populations, yet varies considerably even among healthy young adults with normal hearing. Although SIN skills are known to be influenced by top-down processes that can selectively enhance lower-level sound representations, the complementary role of feed-forward mechanisms and their relationship to musical training is poorly understood. Using a paradigm that minimizes the main top-down factors that have been implicated in SIN performance such as working memory, we aimed to better understand how robust encoding of periodicity in the auditory system (as measured by the frequency-following response) contributes to SIN perception. Using magnetoencephalograpy, we found that the strength of encoding at the fundamental frequency in the brainstem, thalamus, and cortex is correlated with SIN accuracy. The amplitude of the slower cortical P2 wave was previously also shown to be related to SIN accuracy and FFR strength; we use MEG source localization to show that the P2 wave originates in a temporal region anterior to that of the cortical FFR. We also confirm that the observed enhancements were related to the extent and timing of musicianship. These results are consistent with the hypothesis that basic feed-forward sound encoding affects SIN perception by providing better information to later processing stages, and that modifying this process may be one mechanism through which musical training might enhance the auditory networks that subserve both musical and language functions.

Causal relationship between the right auditory cortex and speech-evoked envelope-following response: Evidence from combined transcranial stimulation and electroencephalography

“…The current results validate the previous findings that the right auditory cortex makes significant contributions to speech-evoked FFR (Coffey et al, 2016, 2017a, 2017b; Hartmann and Weisz, 2019) by establishing a causal relationship between the two. To our knowledge, this is the first evidence for this causality and it could be essential due to the fundamental and clinical importance of the FFR.…”

“…Specifically, such effects were present only in the left ear listening condition, indicating that the changes in processing of speech periodicity information occur along the contralateral pathway (i.e., from the left ear to the right auditory cortex). The results thus agree with previous studies that have shown a close relation between the right auditory cortex and FFR (Coffey et al, 2016, 2017a, 2017b; Hartmann and Weisz, 2019) and provide the first evidence for a causal relationship.…”

“…Recent studies, however, have shown an additional source of FFR in the right auditory cortex associated with musical experience, pitch discrimination ability (Coffey et al, 2016), speech-in-noise perception (Coffey et al, 2017a) and intermodal attention (Hartmann and Weisz, 2019). FFR strength is associated with right-lateralized hemodynamic activity in the auditory cortex (Coffey et al, 2017b), consistent with the relative specialization of right auditory cortex for pitch and tonal processing (Zatorre and Berlin, 2001; Patterson et al, 2002; Hyde et al, 2008; Albouy et al, 2013; Cha et al, 2016).…”

“…As such, although after-effects were tested for all three FFR signatures, FFR ENV and FFR TFS_H2 are focused on. In addition, the main effects of Ear for FFR ENV and FFR TFS_F2F3 magnitudes may reflect the laterality of speech encoding at the subcortical (Chandrasekaran and Kraus, 2010; Bidelman, 2015, 2018) and/or cortical levels (Coffey et al, 2016, 2017b), which will be discussed further (see Discussion ).…”

High Gamma Cortical Processing of Continuous Speech in Younger and Older Listeners

“…The neural origins of the FFR have historically been thought to be mainly subcortical areas such as the inferior colliculus (Smith et al, 1975). But recent studies with MEG and EEG have shown that the FFR at ~100 Hz is not purely generated by subcortical areas, but has contributions from the auditory cortex as well (Bidelman, 2018;Coffey et al, 2017bCoffey et al, , 2017aCoffey et al, , 2016Hartmann and Weisz, 2019;Puschmann et al, 2019). Some studies have shown that this cortical contribution is stronger in the right hemisphere (Coffey et al, 2016;Hartmann and Weisz, 2019).…”