It is often difficult to distinguish between the cognitive deficits due to dementia, depression, and normal aging in older adults. This is especially true at the early stages of dementia and with mild depression. It is possible that neuropsychological tests which measure specific dimensions of cognitive functioning may detect differences between these groups. Particularly, measures of recognition memory using signal detection analyses and analysis of trial by trial judgment may be helpful.

This study attempted to discover whether mild depression affects cognitive functioning differently than mild dementia or normal aging using a standardized neuropsychological battery and four experimental measures including a metamemory scale, a stimulus judgment task and two recognition tasks. The recognition tasks utilized positively and negatively toned words and smiling and non-smiling faces. The tasks were administered to 51 older adults who were categorized into mildly depressed, mildly demented, mildly demented and depressed, and non-demented/non-depressed groups and 50 young adults who were categorized into depressed and non-depressed groups.

Demented subjects clearly had poorer performance on the standardized battery, including a measure of discrimination calculated from one subtest. Demented subjects also had poorer discrimination on the experimental wordlist task. Unexpectedly, demented older adults rated their memories lower than non-demented and depressed older adults.

Depression appeared to have an effect on discrimination for non-smiling faces as both young and older depressed adults had better memory for the non-smiling faces than did non-depressed subjects. An interaction was noted between depression and dementia on the measures of response bias for the recognition tasks.

While the young adults had better discrimination for both recognition tasks, scores on the stimulus judgment task and the metamemory scale did not differ across age.

These results suggest that even mild levels of dementia have a strong effect on cognitive functioning. Mild levels of depression may affect memory for nonverbal affective material. Previous research indicating that older adults have a more conservative response bias than young adults, and that demented subjects have a more liberal response bias than non-demented adults, were not supported.