Brainstem correlates of concurrent speech identification in adverse listening conditions

Abstract

When two voices compete, listeners can segregate and identify concurrent speech sounds using pitch (fundamental frequency, F0) and timbre (harmonic) cues. Speech perception is also hindered by the signal-to-noise ratio (SNR). How clear and degraded concurrent speech sounds are represented at early, pre-attentive stages of the auditory system is not well understood. To this end, we measured scalp-recorded frequency-following responses (FFR) from the EEG while human listeners heard two concurrently presented, steady-state (time-invariant) vowels whose F0 differed by zero or four semitones (ST) presented diotically in either clean (no noise) or noise-degraded ( + 5dB SNR) conditions. Listeners also performed a speeded double vowel identification task in which they were required to identify both vowels correctly. Behavioral results showed that speech identification accuracy increased with F0 differences between vowels, and this perceptual F0 benefit was larger for clean compared to noise degraded ( + 5dB SNR) stimuli. Neurophysiological data demonstrated more robust FFR F0 amplitudes for single compared to double vowels and considerably weaker responses in noise. F0 amplitudes showed speech-on-speech masking effects, along with a non-linear constructive interference at 0ST, and suppression effects at 4ST. Correlations showed that FFR F0 amplitudes failed to predict listeners’ identification accuracy. In contrast, FFR F1 amplitudes were associated with faster reaction times, although this correlation was limited to noise conditions. The limited number of brain-behavior associations suggests subcortical activity mainly reflects exogenous processing rather than perceptual correlates of concurrent speech perception. Collectively, our results demonstrate that FFRs reflect pre-attentive coding of concurrent auditory stimuli that only weakly predict the success of identifying concurrent speech.

Bilinguals’ speech perception in noise: Perceptual and neural associations

“…The changes in F0 amplitudes and the shifts in the latency of V peak did not predict accuracy among monolingual listeners. These results align with those of Yellamsetty and Bidelman [ 98 ], who showed that F0 amplitudes failed to predict the accuracy of listeners’ identification, but contradict with others (e.g., [ 34 , 76 , 128 ]) who found a relationship between subcortical neural processing and perceptual performance in noise among monolingual speakers. We suggest that the main reason for not finding a significant perceptual-neural correlation among monolinguals in the current study is that noise deteriorated their perception to a lesser extent compared to bilinguals.…”

“…From the physiological aspect, the responses elicited in noise were diminished and degraded, consistent with previous findings [ 30 , 47 , 76 , 77 , 97 – 99 ]. This reduction can reflect neural desynchronization [ 98 , 100 ] and less efficient efferent processing [ 20 ]. Neural group differences were reflected in noise, where earlier neural latencies were observed in bilinguals compared to their monolingual peers.…”

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

“…The FFR provides insight into the peripheral representation of speech and is a useful tool for investigating temporal processing deficits (Basu et al, 2010;Hornickel et al, 2012;Kraus et al, 2017). In addition, the FFR may be used to investigate the robustness of speech representations in noise or a dual stream paradigm (Yellamsetty and Bidelman, 2019). The FFR is believed to detect the integrated activity of several nonlinear processing stages along the auditory pathway, and hence various nonlinear features of the stimulus can contribute to the FFR (Lerud et al, 2014).…”

Readiness to Learn English for Early Childhood

“…Intellectual factors also influence the readiness of children to learn English (Giroud et al, 2020). Intellectual factors can also affect how children learn a language (Grogan et al, 2012;Yellamsetty & Bidelman, 2019). Children who have an average IQ need more time to understand the contents of the reading compared to children with a high IQ (Bonifacci & Tobia, 2016).…”