PP514 - Neural Measures of Speech Discrimination in English Monolinguals and Spanish-English Bilinguals

With a growing population of Spanish-English bilinguals in the United States, a better understanding of how differences in auditory processing, age of second language acquisition, and language experience can shape how bilinguals process their auditory environment. This leads to the question of “what is the relationship between auditory processing and speech perception as it relates to bilingualism?” The present study explores the automaticity of speech perception between English monolingual and Spanish-English bilingual listeners of temporally-cued contrasts in vowels using a neurophysiological measure known as mismatch negativity (MMN).  

Werker and Tees (1984) found that non-native listeners often show poor discrimination and identification of speech sounds that are non-contrastive in the native language (L1). When non-native listeners attempt to discriminate speech sounds not pertinent to their native language, they will not be able to discriminate and identify those sounds as readily as others, as those sounds hold little importance in understanding the language. Recent research with Spanish-English Bilinguals (BIs) and English Monolinguals have shown that Spanish-English BIs use perceptual-acoustic properties during English speech perception differently from English Monolinguals (Hisagi et al., 2021; Hisagi et al., 2022). These differences may manifest as differences in automaticity of speech perception of temporarily cued contrast. Thus, we hypothesize that there will be a difference in neural responses between monolinguals and Spanish-English BIs.  

In this experiment, we measured Spanish-English BIs and Monolingual English speakers' ability to discriminate between the nonsense Japanese words of /tado/ and /taado/ using a passive listening task during an electroencephalogram (EEG) recording. The words /tado/ and /taado/ are contrasted by the differing duration lengths of the vowels /a/ and /aa/. This difference in vowel length holds linguistic significance in the English language. For example, the vowels /a/ and /æ/ are linguistically and durationally different. However, in Spanish, vowel durations are not linguistically significant. The stimuli were presented in a categorical oddball paradigm with /taado/ presented as the standard and /tado/ presented as the deviant. Long Latency Response (LLR), MMN, were recorded via Brain Vision through an electrode cap as the participant held their attention to a silent movie and listened to the speech sounds passively.  

The result revealed a difference in neural responses between monolinguals and Spanish-English BIs. Monolinguals have a larger MMN, indicating that their speech perception is highly automatic which differs compared to the Spanish-English BIs who presented with small MMNs. Through this difference we can conclude this happens because English monolinguals are accustomed to the temporally-cued contrasts as it is present in the language. 

These findings contribute to our understanding of how changes associated with bilingualism lead to language processing differences and how these changes may impact individuals. This understanding could give Audiologists a better understanding of how bilingualism may affect routine diagnostic clinical evaluations of speech perception. A future direction will be to examine how degraded representation of temporal information due to aging in older populations contributes to impaired speech-perception abilities by evaluating the nature of degradation in the neural encoding of acoustic features.