Reconstructing wholes from parts: effects of modality, age, and hearing loss on word recognition.

OBJECTIVE: In this study, the effects of age, hearing loss, and modality on the ability to integrate partial information in degraded stimuli, either speech or text, were examined using isolated words. It was hypothesized that the ability to make use of partial information in speech diminishes with age. It was also hypothesized that additional contributions of cochlear pathology underlying hearing loss would be manifest as a further decrement in performance for older adults with hearing loss, relative to older adults with normal hearing. Furthermore, it was hypothesized that, if the ability to integrate partial information in speech is amodal, then recognition performance for degraded speech would be associated with recognition performance for parallel measures of degraded text. Last, it was hypothesized that, if the nature of the amodal ability to integrate partial information is cognitive, then the performance on auditory and visual measures of word recognition would be correlated with performance on measures of working memory.
DESIGN: Twenty-five young adults with normal hearing, 20 older adults with normal hearing, and 21 older adults with hearing loss participated in this study. All participants completed three auditory and two parallel visual tasks consisting of listening to or reading degraded words or text. Older participants also completed a working-memory test battery. Group effects were examined for each of the auditory and visual measures. Performance of older participants on cognitive measures was compared with available data from a younger group participating in a different study in our laboratory (with similar protocol). Correlations between auditory and visual measures of speech recognition were examined for all participants. In addition, correlations between perceptual and cognitive measures were computed for the older participants. Finally, the relationship between dependent auditory measures and other independent measures in older adults were further examined using stepwise linear regression analyses.
RESULTS: Of the 10 possible comparisons between the young and the two older groups for the five primary dependent measures, the young performed significantly better than the elderly did, 8 of the 10 times. The two older groups performed similarly for most tasks. In young adults, performance among the auditory tasks and between the two visual tasks was significantly and moderately to strongly correlated. In addition, performance on one of the visual tasks was weakly to moderately significantly correlated with performance on each of the three auditory tasks. Similar moderate to strong correlations were found within the auditory and visual modalities in older adults. However, none of the between-modality correlations were significant in the elderly.
CONCLUSIONS: In summary, the results of this study suggest that the ability to integrate partial information in degraded words diminishes with age. Once audibility is accounted for, this ability does not seem to diminish with cochlear pathology. In young adults, both modality-specific factors and amodal cognitive factors seem to contribute to this ability. In older adults, although modality-specific factors continue to be important, it seems that the perceptual mechanisms that underlie the processing of degraded speech and text are separate, at least for isolated words. Our results suggest that, when peripheral factors are accounted for, some higher-level, yet-to-be identified, age-related factors contribute to speech-communication difficulties in the elderly.