The Effects of Bilingualism on Speech Evoked Brainstem Responses Recorded in Quiet and in Noise
The main objective of the present study was to investigate the effect of sensory enrichment, such as bilingualism, on the subcortical processing in quiet and adverse listening conditions such as in the presence of noise. More specifically, the aim of this investigation was to identify some neural biomarkers at brainstem level distinguishing bilinguals from monolinguals. Forty-one 18- to 25-year-old adults participated in the study: 19 monolinguals and 22 bilinguals. Their language fluency was assessed with the Language Experience and Proficiency (LEAP) questionnaire. Auditory Brainstem Responses (ABRs) were recorded using click and speech /da/ stimuli in quiet and also in noise for the latter. No significant differences between the two groups were observed for click-evoked ABR. The speech-evoked ABR transient waves (V, C) and the periodic region (D and F) latencies were longer for the monolinguals compared to the bilingual group. The Frequency Following Responses (F0 and F1) of the speech-evoked ABR were similar for the two groups in quiet and in noise. Results suggested that monolinguals need more time to process speech stimuli than their bilingual peers. Early in the auditory system, the neural responses related to speech processing in the absence or the presence of background noise seem to be less resilient when compared to those of adults who are fluent in two languages. Bilingualism could stimulate the automatic sound processing abilities of the auditory system in a way that makes it highly efficient. Furthermore, this study demonstrated the applications of speech-ABR and its potential usefulness as a clinical biomarker.
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