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Abstract:
Difficulty naming objects increases with age and dementia. To
investigate the effects of age and Alzheimer's Disease (AD) on the
link between an object and its name, we are using the N400
component of the event-related brain potential (ERP). Because N400
is larger to unprimed than primed words, it is elicited by a word
that does not name an object preceding it. This effect should be
reduced when knowledge of an object's name is degraded by age or
AD. We report preliminary data from 11 AD patients, 7 old controls
(OC), and 6 young controls (YC). Subjects saw line-drawings of
objects followed 1.5 sec later by words that either named (press
one response key) or did not name the objects (press other key).
Items were split according to frequency in English. Early
components at occipital sites (P1 at 100 msec, N1 at 150 msec) to
both words and pictures were not affected by age or disease. Primed
words were associated with faster reaction times (RTs) than
unprimed words. Both age and disease slowed RTs, but neither
affected RT priming. As expected, N400 was larger to unprimed than
primed words, especially at right and midline scalp sites. Age and
disease effects on N400 priming depended on item frequency; N400
indicated strong associations between objects and their names for
all items in YC, only for high frequency items in OC, and for
neither in AD. NIMH (MH40052, MH40041 and MH30854), CA Alzheimer's
Disease Program, DVA.
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