Research reportEffects of brief time delays on matching-to-sample abilities in capuchin monkeys (Sapajus spp.)

- We examine capuchin monkeys' ability to match visual stimuli after brief delays.
- 0.5 s intervals do not affect either response accuracy or response time.
- 1.0 s intervals do not affect response accuracy but increase response time.
- 2.0 and 3.0 s intervals decrease response accuracy and increase response time.
- Effects consistent with those ascribed to iconic memory in humans.

Traditionally, studies of delayed matching-to-sample (DMTS) tasks in nonhuman species have focused on the assessment of the limits of the retrieval of information stored in short- and long-term memory systems. However, it is still unclear if visual recognition in these tasks is affected by very brief delay intervals, which are typically used to study rapidly decaying types of visual memory. This study aimed at evaluating if tufted capuchin monkeys' ability to recognise visual stimuli in a DMTS task is affected by (i) the disappearance of the sample stimulus and (ii) the introduction of delay intervals (0.5, 1.0, 2.0 and 3.0 s) between the disappearance of the sample and the presentation of the comparison stimuli. The results demonstrated that the simple disappearance of the sample and the introduction of a delay of 0.5 s did not affect capuchins' performance either in terms of accuracy or response time. A delay interval of 1.0 s produced a significant increase in response time but still did not affect recognition accuracy. By contrast, delays of 2.0 and 3.0 s determined a significant increase in response time and a reduction in recognition accuracy. These findings indicate the existence in capuchin monkeys of processes enabling a very accurate retention of stimulus features within time frames comparable to those reported for humans' sensory memory (0.5-1.0 s). The extent to which such processes can be considered analogous to the sensory memory processes observed in human visual cognition is discussed.