Psychometric function for NU-6 word recognition in noise: effects of first language and dominant language

The present study attempted to establish psychometric function in individuals whose first language is not English. Psychometric function was obtained for one of the most commonly used clinical tests, the Northwestern University Auditory Test No. 6 (Tillman & Carhart 1966), so that findings could be directly applied to everyday clinical practice.

Five groups of 14 normal-hearing, adult listeners differing in their first language and dominant language (English monolinguals, English- and Arabic-dominant Arabic-English bilinguals, and English- and Russian-dominant Russian-English bilinguals) participated. Both forms of the Northwestern University Auditory Test No. 6 test (8 lists of 50 monosyllabic English words) were presented. The lists were randomly assigned to eight signal-to-noise ratios (-3 to 18 dB in 3 dB steps). Listeners responded verbally and in writing. Psychometric functions were derived via logistic regression and described by two parameters: the 50% correct performance level (θ) and the slope (k).

Both English-dominant bilingual groups obtained psychometric functions comparable with monolinguals. The θ and k of the functions for these three groups of participants were consistent with the literature. Compared with these three groups, non-English-dominant bilinguals' functions grew significantly more gradually (i.e., a significantly higher θ and a significantly lower k). No differences in either θ or k were found between bilinguals with the same dominant language but different first languages.

Bilinguals reporting themselves to be dominant in English generate monolingual-like psychometric functions. By contrast, a different set of psychometric properties describes the function of bilinguals dominant in their first language. Because first language did not appear to be a significant factor in determining bilinguals' functions, it is concluded that English learning history and English proficiency are more important variables than first language for clinicians to consider when administering English word-recognition tests to their bilingual clients. When working with bilingual clients who are dominant in their first language, clinicians are advised to refer to the normative data reported here specifically for these individuals.