Monkeys, movements, and memories: Behavioral sequences and short-term memory in aged monkeys.

Abstract

Six young and six old squirrel monkeys were tested on two different short-term memory tasks. One was a two-choice problem, the other a nine-choice problem. A baseline, or one-choice, problem was also included. A video camera recorded all behaviors displayed by the monkeys during testing. Behaviors coded were turning, aggression, displacement, exploratory, huddling, orienting, locomotion, screen activities, and visual scanning. Also recorded was correct or incorrect choice and whether the animal showed evidence of seeing the cue stimulus. Old animals committed more errors during both phases of the experiment. Older animals were also more likely to engage in active behaviors, such as turning, whereas young animals were more likely to manifest less active behaviors, such as visual scanning and orienting. Young animals were also more likely to see the stimulus. A path analytic procedure was used to determine direct effects of age on performance and indirect effects mediated through behaviors manifested prior to the choice. For the two-choice problem, approximately half of the age effects on performance were attributable to indirect effects. For the nine-choice problem almost three quarters of the age effects on performance were attributable to indirect effects. These findings indicate that age differences in short-term memory performance are not direct effects of age alone. The age effect also occurs because age affects the behaviors of the monkeys and that these behaviors have a large effect on subsequent memory performance.