Alzheimer patients show a sensitivity decrement over time on a tonic alertness task.

Tonic alertness was investigated in Alzheimer patients and normal elderly subjects. Sensitivity and criterion shifts were investigated across 45 min of continuous testing using a high event rate test with very low target probability. Alzheimer patients showed a significant sensitivity decrement over time that was unrelated to dementia severity. These results suggest that tonic alertness is impaired by Alzheimer's disease even in its early stages.