Bilingualism and Speech Understanding in Noise: Auditory and Linguistic Factors.

Abstract

Bilingual speakers often have difficulty understanding speech in noisy and acoustically degraded conditions. The first aim was to examine the potential source(s) of the difficulties that English-proficient bilingual listeners experience when hearing English speech in noise. The second aim was to assess how bilingual listeners perform on a battery of central auditory processing tests. A mixed design was used in this study. Normal-hearing college students (n = 24) participated in this study. The bilingual participants (n = 12) self-reported that they learned a second language before age 9 and the monolingual participants reported that they only knew American English. All participants considered themselves to be native speakers of American English. Participants were administered the Revised Speech Perception in Noise (R-SPIN) test to assess whether bilingual listeners' speech understanding in noise reflects auditory factors, linguistic factors, or a combination of the two. To minimize the influence of short-term memory and motor movements, only the final word of a sentence is repeated for this test. Sentence-final words were presented in two linguistic contexts: in the high-predictability condition, the final word can be deduced from the context created by the preceding words, and in the low-predictability condition, it cannot. The R-SPIN test was administered at two signal-to-noise ratios (SNRs) (0 and 3 dB). In addition, the participants were given a reading comprehension test to measure their ability to use context when linguistic stimuli are delivered to the visual, not auditory, modality. The central auditory test battery consisted of three tests: Competing Sentences, Dichotic Digits, and NU-6 Time-Compressed Speech with Reverberation. All test materials were given in American English. The bilingual and monolingual groups performed similarly in the low-context condition of the R-SPIN test. However, in comparison to the age-matched monolingual group, the bilingual group did not derive the same level of benefit from contextual cues, as seen by a smaller improvement in performance between the low- and high-predictability R-SPIN conditions. The bilingual and monolingual groups showed a similar decrement in performance when the SNR dropped. In addition, bilingual individuals underperformed on the Competing Sentences test when instructed to attend to the left ear. However, the bilingual and monolingual groups performed equally well on the reading comprehension test, as well as on the Time-Compressed Speech with Reverberation and Dichotic Digits tests. We show that individuals who are exposed to two languages from an early age, and self-report as having a high level of proficiency in English, perform like their monolingual counterparts in acoustically degraded conditions where context is not facilitative, but they underperform in conditions where sentence-level linguistic context is facilitative to understanding. We conclude that deficits observed in noise are likely not due to a perceptual deficit or a lack of linguistic competence, but instead reflect a linguistic system that performs inefficiently in noise. In addition, we do not find evidence of an auditory processing weakness or advantage in our bilingual cohort; however, the use of speech materials to assess auditory processing is a confound.