Response bias for picture recognition in patients with Alzheimer disease.

Objective—To investigate whether changing recognition stimuli from words to pictures would alter response bias in patients with Alzheimer's disease (AD). Background—Response bias is an important aspect of memory performance in patients with AD, as they show an abnormally liberal response bias compared to healthy older adults. We have previously found that despite changes in discrimination produced by varying the study and test list length, response bias remained remarkably stable in both patients with AD and older adult controls. Methods—Patients with mild AD and healthy older adults underwent two separate study-test sessions of pictures and words. For both pictures and words, increasing study-test list lengths were used to determine whether bias changed as a factor of discrimination or task difficulty. Results—Consistent with apriori hypotheses, healthy older adults showed increased discrimination and shifted to a more liberal response bias for pictures compared to words. In contrast, despite their higher level of discrimination for pictures, patients with AD showed a similar response bias for both pictures and words. Bias was consistent across varying study-test lengths for both groups. Conclusions—These results suggest that response bias is a relatively invariant factor of an individual with AD that remains liberal regardless of discrimination or stimulus type.