Automatic and effortful processing in aging and dementia: event-related brain potentials.

Automatic and effortful processes were investigated using event-related brain potentials (ERPs) recorded from moderately impaired subjects with probable Alzheimer's Disease (AD), normal elderly, and normal young controls. The effects of effortful attention on ERPs to loud noises and the effects of stimulus intrusiveness on effortfully elicited ERPs were studied. First, ERPs to task relevant and irrelevant startling noises were compared. Second, ERPs to startling noises and moderate tones were compared when both were targets. The effects of age (young vs. elderly controls) and effects of dementing disease (AD subjects vs. elderly controls) were also assessed. Effortful attention augmented noise-elicited P300 amplitude in elderly subjects, but not in young. Intrusiveness augmented task-relevant P300 amplitude in young subjects, but not in elderly. Neither variable affected P300 amplitude in AD subjects. Thus, effects of age and disease depended on how P300 was elicited: when effortfully elicited, P300 amplitude was affected by disease but not age; when automatically elicited, P300 amplitude was affected by age but not disease. N1 effects differed from P300 effects.