Acquisition and maintenance of delayed matching-to-sample in tufted capuchin monkeys

Delayed matching-to-sample (DMTS) is a commonly used procedure to investigate short-term memory. For the study of functions of forgetting, the delay between the disappearance of the sample stimulus and appearance of choices is manipulated. The intertrial interval (ITI) is also varied to assess interference effects. Performance decrements have been observed as delay increases and, in some cases, performance recovery occurs when ITIs are increased. Other studies indicate that the higher the ITI/delay ratio, the greater the accuracy in DMTS. In this study, 2 experiments investigated DMTS performances of 3 tufted capuchin monkeys as function of delay and ITI. In Experiment 1, alternation of gradual increases of delay and ITI was effective in producing ≥90% accuracy at delays as long as 90 s. Individual monkeys differed in the highest value of delay at which this criterion was met. In Experiment 2, the monkeys were exposed to 5-s DMTS with different ITIs to assess the effects of various ITI/delay ratios on accuracy. Highest accuracy tended to occur at the higher ITI/delay ratios.