Background: In addition to declines in auditory acuity, adult aging is often also accompanied by reduced cognitive efficiency, most notably in working memory resources and a general slowing in a number of perceptual and cognitive domains. Effectiveness of speech comprehension by older adults reflects a balance between these declines and the relative preservation in healthy aging of linguistic knowledge and the procedural rules for its application.
Purpose: To examine effects of hearing acuity in older adults on intelligibility functions for sentences that varied in two degrees of syntactic complexity, with their concomitant demands on older adults' working memory resources.
Research design: Stimuli consisted of monosyllabic words presented in isolation, and nine-word sentences that varied in syntactic complexity. Two sentence types were employed: sentences with a subject-relative clause structure, and more syntactically complex sentences in which meaning was expressed with an object-relative clause structure. The stimuli were presented initially below the level of audibility and then increased in loudness in 2 dB increments until the single-word stimuli and all nine words of the sentence stimuli could be correctly reported.
Study sample: Participants were 16 older adults with good hearing acuity for their ages, 16 age-matched adults with mild-to-moderate hearing loss, and 16 young adults with age-normal hearing.
Results: Along with confirming better report accuracy for the words of meaningful sentences than for words heard in isolation, performance curves for the sentence stimuli showed a significant effect of syntactic complexity. This took the form of older adults having poorer report accuracy at any given loudness level for sentences with greater syntactic complexity. This general effect of syntactic complexity on perceptual report accuracy was further exacerbated by age and hearing loss.
Conclusions: Age-limited working memory resources are impacted both by the resource demands required for comprehension of syntactically complex sentences and by effortful listening attendant to hearing loss.