Influences of working memory and audibility on word learning in children with hearing loss

As a group, children with hearing loss demonstrate delays in language development relative to their peers with normal hearing. Early intervention has a profound impact on language outcomes in children with hearing loss. Data examining the relationship between degree of hearing loss and language outcomes are variable. Two approaches are used in the current study to examine this variability. The first approach compares the working memory system of children with hearing loss to that of children with normal hearing. The second approach uses regression analyses to determine whether aided speech audibility or pure tone threshold is a stronger predictor of language outcomes.;Sixteen children with mild to moderately-severe hearing loss fit with bilateral amplification (CMML) and 24 children with normal hearing (CNH) between 6 and 9 years of age participated in the study. Over two visits, participants underwent a battery of tests including measures of auditory perception, working memory, word learning, and vocabulary level. Parents completed questionnaires about their child's behavior and executive skills.;There was little difference between CMML and CNH on measures of working memory involving phonologically predictable stimuli (i.e., numbers), including forward and backward digit span and phonological coding bias. Regardless of hearing status, children with poorer executive skills demonstrated reduced efficiency on the forward digit span task. Compared to CNH, CMML had a slower articulation rate, an index of phonological working memory efficiency, and poorer performance on nonword repetition, a working memory task of higher phonological complexity than digit span.;The measure of speech audibility, the aided Speech Intelligibility Index (SII), was a stronger predictor of nonword repetition score and receptive vocabulary level than pure-tone average, spectral peak resolution, age of identification, or age of intervention. The robust predictive value of aided SII is attributed to the incorporation of speech band importance and hearing aid response in its algorithm.;As a group, CMML do not demonstrate the degree of working memory deficits seen in children with profound hearing loss [Pisoni, D. B., & Geers, A. E. (2000). Working memory in deaf children with cochlear implants: correlations between digit span and measures of spoken language processing. Annals of Otology, Rhinology and Laryngology, 185s, 92-93.]. Of the variables included in this study, decreased audibility had the most devastating effects on word recognition and vocabulary development. The results support the recommendation that audibility measurements be used as an independent variable in research on CMML language development. Aided SII should be calculated for all children fit with hearing aids and used to flag children at risk for delayed vocabulary development.