Aging and Word Retrieval: How Aging-Related Gains in Semantic Knowledge and Loss of Access to Linguistic Information are Expressed in Connected Speech.

摘要

As people age, they accumulate word knowledge, or vocabulary, yet their ability to access individual words at a given moment decreases. Indeed, in studies of naturalistic connected speech, or discourse, older adults are found to produce more unique words than younger adults; yet they are also more likely to experience tip-of-the-tongue occurrences and produce more errors in speech. Evidence from laboratory studies suggests that degradation of neural networks may underlie these word-access deficits. The purpose of the present study was to determine whether older adults produce more atypical language than younger adults because they must compensate for word-retrieval errors by substituting less normative language, or because they are better equipped to maximize their available vocabulary on account of more experience with communication. Additional analyses were directed to test the hypotheses that older adults would be least likely to produce words of low lexical frequency as well as words subject to high levels of semantic competition. To address these questions, 60 younger and 60 older adults described two neutral photographs. Their words were assessed for accuracy and precision by a second sample of 48 high-vocabulary younger and older adults. For each word, the proportion of participants who used that word to describe a particular object or action depicted in the pictures ( normativeness) was determined. Additionally the overall frequency of use in the English language and level of semantic competition were assessed based on available published norms. As predicted, older adults produced non-normative words at a greater rate than younger adults. However, there was evidence that they did so both to maximize their available vocabulary but also as a way of compensating for word-access failures. Overall, older adults did not struggle to produce words that were low-frequency or subject to high levels of competition. However, when they exhibited evidence of deliberating over word choice, they failed to produce such words. Moreover, the quality of their word choice also suffered from deliberative searches. These findings are discussed in relation to the neural-network models posed by Node-Structure Theory (Mackay & Burke, 1990) and lexical competition accounts of word production and aging (e.g., Levelt, Roelofs, & Meyer, 1999).