Regardless of whether language is written or spoken, the input to the comprehender becomes available over time and temporally discontinuous parts of the input must be related to one another for language to be understood. Thus, language comprehension must involve a temporary store or working memory system. Some decrements in language comprehension have been hypothesized to be related to decrements in working memory capacity. Working memory capacity declines with age and this decline has in turn been related to reductions in other cognitive capacities, in particular the speed with which cognitive operations can be carried out. While WM, processing speed and language comprehension are certainly related in some way, the exact nature of the connections between them is not fully understood. A basic question is the extent to which changes in language processing, WM and speed of processing are unitary vs. the extent to which they can dissociate. Some aspects of language comprehension are greatly over practiced and may not be affected by WM limitations or processing speed reductions that appear in other verbal tasks. The proposed research will investigate the relationship between language comprehension, WM and speed of processing by characterizing and relating language comprehension (at the levels of sentences and discourse), WM and processing speed in elderly participants and AD patients. The research will mainly use behavioral approaches, but will also employ functional neuroimaging to provide a different source of data regarding these relationships.
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