Relationships among speech perception, production, language, hearing loss, and age in children with impaired hearing

Eighty-seven primary-school children with impaired hearing were evaluated using speech perception, production, and language measures over a 3-year period. Forty-seven children with a mean unaided pure-tone-average hearing loss of 106 dB HL used a 22-electrode cochlear implant, and 40 with a mean unaided pure-tone-average hearing loss of 78 dB HL were fitted with hearing aids. All children were enrolled in oral/aural habilitation programs, and most attended integrated classes with normally hearing children for part of the time at school. Multiple linear regression was used to describe the relationships among the speech perception, production, and language measures, and the trends over time. Little difference in the level of performance and trends was found for the two groups of children, so the perceptual effect of the implant is equivalent, on average, to an improvement of about 28 dB in hearing thresholds. Scores on the Peabody Picture Vocabulary Test (PPVT) and the Clinical Evaluation of Language Fundamentals showed an upward trend at about 60% of the rate for normally hearing children. Rates of improvement for individual children were not correlated significantly with degree of hearing loss. The children showed a wide scatter about the average speech production score of 40% of words correctly produced in spontaneous conversations, with no significant upward trend with age. Scores on the open-set Consonant-Nucleus-Consonant (CNC) monosyllabic word test and the Bench-Kowal-Bamford (BKB) sentence test were strongly related to language level (as measured by an equivalent age on the PPVT) and speech production scores for both auditory-visual and auditory test conditions. After allowing for differences in language, speech perception scores in the auditory test condition showed a slight downward trend over time, which is consistent with the known biological effects of hearing loss on the auditory periphery and brainstem. Speech perception scores in the auditory condition also decreased significantly by about 5% for every 10 dB of hearing loss in the hearing aid group. The regression analysis model allows separation of the effects of language, speech production, and hearing levels on speech perception scores so that the effects of habilitation and training in these areas can be observed and/or predicted. The model suggests that most of the children in the study will reach a level of over 90% sentence recognition in the auditory-visual condition when their language becomes equivalent to that of a normally hearing 7-year-old, but they will enter secondary school at age 12 with an average language delay of about 4 or 5 years unless they receive concentrated and effective language training.