Relationship between age of hearing-loss onset, hearing-loss duration, and speech recognition in individuals with severe-to-profound high-frequency hearing loss.

The factors responsible for interindividual differences in speech-understanding ability among hearing-impaired listeners are not well understood. Although audibility has been found to account for some of this variability, other factors may play a role. This study sought to examine whether part of the large interindividual variability of speech-recognition performance in individuals with severe-to-profound high-frequency hearing loss could be accounted for by differences in hearing-loss onset type (early, progressive, or sudden), age at hearing-loss onset, or hearing-loss duration. Other potential factors including age, hearing thresholds, speech-presentation levels, and speech audibility were controlled. Percent-correct (PC) scores for syllables in dissyllabic words, which were either unprocessed or lowpass filtered at cutoff frequencies ranging from 250 to 2,000 Hz, were measured in 20 subjects (40 ears) with severe-to-profound hearing losses above 1 kHz. For comparison purposes, 20 normal-hearing subjects (20 ears) were also tested using the same filtering conditions and a range of speech levels (10-80 dB SPL). Significantly higher asymptotic PCs were observed in the early (<=4 years) hearing-loss onset group than in both the progressive- and sudden-onset groups, even though the three groups did not differ significantly with respect to age, hearing thresholds, or speech audibility. In addition, significant negative correlations between PC and hearing-loss onset age, and positive correlations between PC and hearing-loss duration were observed. These variables accounted for a greater proportion of the variance in speech-intelligibility scores than, and were not significantly correlated with, speech audibility, as quantified using a variant of the articulation index. Although the lack of statistical independence between hearing-loss onset type, hearing-loss onset age, hearing-loss duration, and age complicate and limit the interpretation of the results, these findings indicate that other variables than audibility can influence speech intelligibility in listeners with severe-to-profound high-frequency hearing loss.