Linking Auditory Processing and Lexical Representation Via Phonological Discrimination
Objectives: The purpose of this project is to study the connections between auditory processing and language learning using a phonological discrimination task, which by hypothesis links early auditory processing and macro-level language competency. The overarching goal is to understand the role of consistency of sound processing in early word learning by looking at its effect on phonological discrimination.
Methods: Sixteen children participated in the study, eight typically developing (TD) (two girls) with a mean age of 11.25 (1.9) years and eight diagnosed with ASD (one girl) with a mean age of 12.5 (3.59) years. All participants were first screened for normal hearing thresholds. ABRs were recorded in response to a “da” stimulus (10.9/sec, 6000 trials) presented at 80 dB SPL. To assess phonological discrimination, pairs of bisyllabic CVC-CVC (consonant-vowel-consonant) novel words that differed by only one phonemic unit (biskar vs. bisdar) or were identical (selzim vs. selzim) were presented, and the child was asked if they were the same or different. Current language ability was measured using four subtests of the Clinical Evaluation of Language Fundamentals 5 (CELF-5); Word Classes, Formulated Sentences, Repeated Sentences, and Following Directions.
Results: The TD group performed significantly more accurately on phonological discrimination than the ASD group (t(14)= 2.84, p= 0.023). Neural response consistency was positively correlated with phonological discrimination ability in the ASD group (r=0.825, p= 0.014) but not in the TD group (r= 0.213, ns). Bivariate correlations including both groups found that children with better phonological discrimination also had higher standard scores on all CELF 5 subtests (rs> 0.747, ps < 0.001). The relationship between neural response consistency and language ability (Formulated Sentences and Word Classes) was mediated by phonological discrimination, as indicated by a Sobel test (z’s>2.28, ps <0.02).
Conclusions: Phonological discrimination appears to mediate the relationship between neural response consistency to speech sounds and current language ability. Neural consistency may engender firmer phonological representations that encourage word-learning as well as more advanced language development. As group differences were not observed between TD and ASD this may indicate that similar processes are at work in both typical and atypical populations. Greater heterogeneity within the ASD sample may account for more pronounced relationships between phonological discrimination and neural responses.