The present study sought to identify factors that would be associated with speech understandingin noise (SUN) ability in monolingual and bilingual listeners. The Ease of LanguageUnderstanding (ELU) model predicts that mismatches between the speech signal andphonological representations stored in long-term memory (LTM) will result in greater explicitprocessing effort and, as a consequence, decreased comprehension. Such mismatches can be theresult of signal degradations or imprecise lexical representations in LTM. Based on the lexicalquality hypothesis (Perfetti & Hart, 2002; Perfetti, 2007), it was hypothesized that the quality oflexical representations would differ within speakers as a function of word frequency and betweenspeakers a function of overall language experience, operationalized here as vocabularyknowledge. From these assumptions it followed that bilingual speakers would have less preciselexical representations than monolinguals because of their reduced language experience as aresult of speaking two languages. A second hypothesis was that the same relationship betweenvocabulary knowledge and SUN exists in monolingual and bilingual speakers.The present study tested these predictions in a sample of 53 English monolingual and 48early Spanish-English bilingual speakers with a mean age of 20.7 years (SD = 2.6, range = 18-31). All participants completed two subtests of verbal ability (picture vocabulary and verbalanalogies) from the Woodcock-Muñoz Language Survey (WMLS), a standardized test ofEnglish. In addition, participants completed tests that were believed to be associated with SUN, averbal WM test, a nonlinguistic test of auditory attention, and a consonant perception in noisetest. SUN was tested using sentences from a previously published test, the Speech Perception inNoise (SPIN) test (Bilger, Nuetzel, Rabinowitz, & Rzeczkowski, 1984), at two signal-to-noiseratios (SNR; 3 dB and -2dB), using multi-talker background babble as the noise masker. Theparticipants’ task was to type the last word of the sentence, which was either predictable fromcontext (e.g., The ship sailed along the coast) or nonpredictable (e.g., Mrs. Brown did notconsider the coast).When looking at group differences, the results replicated previous studies, showing thatbilinguals recognized target words with lower accuracy relative to monolinguals. In addition,monolinguals benefitted more from a predictive context than bilinguals. The results from theWMLS showed that bilinguals scored significantly lower than monolinguals. When Englishproficiency was used as a covariate, higher proficiency was associated with higher SUNaccuracy in both groups. In addition, an analysis of word frequency showed that groupdifferences were largest for low frequency words. However, the frequency effect was modulatedby English proficiency in the bilingual group. Assuming that both the frequency effect andlanguage proficiency are closely related to exposure to English, the present results suggest thatthe bilingual disadvantage in SUN results from reduced exposure to English, which is aconsequence of being exposed to two languages.In conclusion, the results confirmed the predictions of the ELU, showing that both signaldegradations and receiver limitations (less precise phonological representations of words inLTM) resulted in less accurate SUN ability.
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