Cognitive resources during sentence processing in Alzheimer's disease.
This study assessed sentence comprehension in Alzheimer's disease (AD) while minimizing executive resource demands. AD patients (n=17) and healthy elderly control subjects (n=17) were asked to detect a word in a sentence. Unbeknownst to subjects, the target word at times followed an incorrect grammatical or semantic agreement. Control subjects took significantly longer to respond to a target word when it immediately followed an agreement violation compared to a coherent agreement, a difference that was not evident when the target word followed the agreement by several syllables. AD patients did not demonstrate a discrepancy between a violation and a coherent agreement in the immediate vicinity of the agreement, but demonstrated a significant delay in their response to a target word when it followed an agreement violation--particularly a violation of a grammatical agreement--by several syllables. Analyses of individual patient performance profiles revealed the pattern of delayed sensitivity to agreements in a majority of AD patients. Correlation and regression analyses associated AD patients' sensitivity to agreement violations over an abnormally delayed time course with a measure of inhibitory control, although weaker associations were also evident with measures of planning and short-term memory. We hypothesize that difficulty understanding grammatically complex sentences in AD is related to slowed information processing speed that restricts the timely construction of a sentence's structure and limits inhibition of canonical sentence interpretations such as first-noun-is-subject.
Grossman
M
M
Department of Neurology - 3 Gates, University of Pennsylvania Medical Center, 3400 Spruce Street, Philadelphia, PA 19104-4283, USA. mgrossma@mail.med.upenn.edu
Rhee
J
J
D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000523:psychology*; D016022:Case-Control Studies; D003071:Cognition; D016002:Discriminant Analysis; D005260:Female; D006801:Humans; D007266:Inhibition, Psychological; D008297:Male; D008570:Memory, Short-Term; D009483:Neuropsychological Tests; D012660:Semantics; D012720:Severity of Illness Index