Working memory in older subjects: dealing with ongoing and stored information in language comprehension

The purpose of this experiment was to investigate the role of aging in working memory (WM), or at least the part involved in language comprehension, e.g., a double function of processing the ongoing information and keeping in memory the product of this processing. Young and older subjects were asked to simultaneously detect incongruities in sentences and keep increasing longer series of words (3, 4, or 5) in memory. The difficulty of incongruity detection was manipulated by variation of the number of intervening words (0, 6, or 12) between two critical words. Incongruity detection was assumed to be linked to the processing of information function of working memory. The concurrent mnemonic load consisted of material previously processed, and was assumed to be linked to the storage function of WM. Results showed that an increment in incongruity-detection difficulty led to a greater decrement in accuracy in older than in young subjects, indicating an impairment in the information-processing function. On the other hand, an increment in concurrent mnemonic load led to a slightly smaller decrement in accuracy in older subjects. Furthermore, fewer words from this mnemonic load were recalled in older subjects. It is suggested that older subjects are impaired in coping with both requirements of the task, and tend to sacrifice the storage of information recently processed to devote their resources to the immediate processing component of the task. These results are discussed in relation to their implications for language comprehension.