The resolution of lexical ambiguity with reference to context in dementia of the Alzheimer's type

The present study investigated how a dementing illness such as Alzheimer's disease, might affect an individual's recourse to higher order contextual i nformation in the access and integration of lexical material in on-line dis course comprehension. More specifically, the experiment investigated the pr iming of homophones in a discourse context, by use of a cross-modal lexical decision task, and compared the performances of a group of six subjects wi th mild to moderate dementia of the Alzheimer's type (DAT) with those of a matched control group. The subjects listened to 2-sentence paragraphs and p erformed a lexical decision on visually presented targets that followed amb iguous prime words (or homophones) at two inter-stimulus intervals (ISIs): 330 and 1000 msec. When the target was a word, it was either an associate o f the prime word, a probable inference suggested by the discourse, or an un related word. The control subjects primed both the discourse-appropriate an d discourse-inappropriate associate of the homophone at short (330 msec) IS Is (but not an appropriate inference word), a finding which supports the ex haustive access model of ambiguity resolution. As the ISI was lengthened to 1000 msec, however, the discourse-appropriate inference word was primed, a nd reflects the operation of attention-dependent integrative strategies. Th e subjects with DAT primed both appropriate associates and inference words at the short ISI. At ISI of 1000 msec, the DAT subjects primed the appropri ate associate and showed substantial inhibition priming of the inappropriat e associate. These results point to disturbances in the selective automatic activation of lexical material, and in the conscious integration and elabo ration of lexical material in ongoing discourse comprehension in persons wi th DAT.