Impact of adult age and Alzheimer's disease on levels of neural noise for letter matching.
We tested healthy young and older adults as well as higher-scoring (Mini-Mental State Exam, MMSE, scores between 14-20) and lower-scoring patients diagnosed with probable Alzheimer's disease (AD) on a letter-matching task. Subjects were instructed to respond "same" if two simultaneously presented letters were identical, or "different" if the letters did not match. Healthy older adults showed a larger "fast-same" effect than healthy young adults. Also, higher-scoring AD patients showed a large "false-different" effect for errors, but lower-scoring AD patients showed a large "false-same" effect. These data indicate that older adults exhibit higher neural noise levels than younger adults. The cross-over error pattern for AD suggests that moderately demented AD patients show evidence of forming degraded visual percepts whereas more severely demented AD patients show evidence of forming incomplete percepts.
Allen
P A
PA
Department of Psychology, Cleveland State University, OH 44115.
Namazi
K H
KH
Patterson
M B
MB
Crozier
L C
LC
Groth
K E
KE
D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D000544:Alzheimer Disease / Q000503:physiopathology* / Q000523:psychology; D006801:Humans; D009410:Nerve Degeneration; D009474:Neurons / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation; D011930:Reaction Time / Q000502:physiology