Consequences of bilingualism for speech understanding in noise

CONSEQUENCES OF BILINGUALISM FOR SPEECH UNDERSTANDING IN NOISE By Jens Schmidtke The present study sought to identify factors that would be associated with speech understanding in noise (SUN) ability in monolingual and bilingual listeners. The Ease of Language Understanding (ELU) model predicts that mismatches between the speech signal and phonological representations stored in long-term memory (LTM) will result in greater explicit processing effort and, as a consequence, decreased comprehension. Such mismatches can be the result of signal degradations or imprecise lexical representations in LTM. Based on the lexical quality hypothesis (Perfetti & Hart, 2002; Perfetti, 2007), it was hypothesized that the quality of lexical representations would differ within speakers as a function of word frequency and between speakers a function of overall language experience, operationalized here as vocabulary knowledge. From these assumptions it followed that bilingual speakers would have less precise lexical representations than monolinguals because of their reduced language experience as a result of speaking two languages. A second hypothesis was that the same relationship between vocabulary knowledge and SUN exists in monolingual and bilingual speakers. The present study tested these predictions in a sample of 53 English monolingual and 48 early Spanish-English bilingual speakers with a mean age of 20.7 years (SD = 2.6, range = 1831). All participants completed two subtests of verbal ability (picture vocabulary and verbal analogies) from the Woodcock-Muñoz Language Survey (WMLS), a standardized test of English. In addition, participants completed tests that were believed to be associated with SUN, a verbal WM test, a nonlinguistic test of auditory attention, and a consonant perception in noise test. SUN was tested using sentences from a previously published test, the Speech Perception in Noise (SPIN) test (Bilger, Nuetzel, Rabinowitz, & Rzeczkowski, 1984), at two signal-to-noise ratios (SNR; 3 dB and -2dB), using multi-talker background babble as the noise masker. The participants’ task was to type the last word of the sentence, which was either predictable from context (e.g., The ship sailed along the coast) or nonpredictable (e.g., Mrs. Brown did not consider the coast). When looking at group differences, the results replicated previous studies, showing that bilinguals recognized target words with lower accuracy relative to monolinguals. In addition, monolinguals benefitted more from a predictive context than bilinguals. The results from the WMLS showed that bilinguals scored significantly lower than monolinguals. When English proficiency was used as a covariate, higher proficiency was associated with higher SUN accuracy in both groups. In addition, an analysis of word frequency showed that group differences were largest for low frequency words. However, the frequency effect was modulated by English proficiency in the bilingual group. Assuming that both the frequency effect and language proficiency are closely related to exposure to English, the present results suggest that the bilingual disadvantage in SUN results from reduced exposure to English, which is a consequence of being exposed to two languages. In conclusion, the results confirmed the predictions of the ELU, showing that both signal degradations and receiver limitations (less precise phonological representations of words in LTM) resulted in less accurate SUN ability.