Abstract:

Language is a complex lifelong faculty supported by the general cognitive system as well as the dynamic interactions between comprehension and production processes within the language system. Studies reported that while normal aging impairs important aspects of language production, most core processes of comprehension are robust. However, accumulating evidence suggests a decline in comprehension when comparing older adults with young ones. Thus it is plausible to assume that there might be a general degradation in older adults’ language capacity. The information-universal theories assume that the aging of language is contributed by the declines in general cognitive abilities including processing speed, working memory and inhibitory function, while the information-specific theories highlight the unique changes of linguistic representations and their connections in the brain, which may result in decreased interplay between comprehension and production.
The current study investigated the relationships among language comprehension capacity, production capacity, and general cognitive abilities, and explored the factors that influence the aging of language processing. We employed two groups of participants (103 young adults and 114 older adults), and measured their general cognitive abilities and language capacities with different tasks. General cognitive abilities were assessed in three dimensions: processing speed by color judgment and numerical judgment tasks, working memory by digit span forward and backward tasks, and inhibitory function by STROOP color-word judgment task. Language comprehension and production capacities were measured at word, sentence and discourse processing levels, respectively.
We first compared the performance between the two age groups, and then conducted hierarchical regression analyses to examine the contributions of information-universal and information-specific factors to language performance. Results showed lower scores in older adults than their young counterparts on all measures. The first hierarchical regression analyses revealed that there were differences between the older and the young groups, which presented not only in the contributions of general cognitive abilities to language capacities but also in the contributions of comprehension and production capacities to each other. For word processing, young adults’ performance was predicted by both general cognitive abilities and the other language capacities, while the former did not predict older adults’ performance; for sentence processing, young adults’ performance was predicted by general cognitive abilities (only in comprehension) and the other language capacities, while neither of them explained older adults’ performance; for discourse processing, young adults’ comprehension scores were predicted by their production capacity, while older adults’ scores of comprehension and production were predicted by their general cognitive abilities and comprehension capacity respectively. Results of the second hierarchical regression analyses indicated that both general cognitive abilities and the other language capacities contributed to the group differences in language performance, and the contributions of the former were larger than those of the latter.
In sum, older adults show an overall age-related decline in general cognitive abilities, language comprehension and production capacities. We suggest that the aging of language processing is subject to both the information- universal factor as well as the information-specific factor, with the former reflected as the general degradation in cognitive abilities and the latter related to specific changes in the architecture of language system.

Key words: cognitive aging, general cognitive abilities, language comprehension, language production, information- universal factor, information-specific factor