Familiarity, Active Memory And Pressure During A Delayed Matching-To-Sample Task In Tufted Capuchin Monkeys (Sapajus [Cebus] Apella)

Delayed matching-to-sample (DMTS) tasks are commonly used in the field of comparative cognition to study memory, including working memory. However, specific task demands vary across studies and species, and as such, DMTS tasks may engage different memory systems when features such as the available stimulus pool differ. Further, individual or species-wide differences in response to pressure to perform may increase variation within a species. We explored how task features, memory systems, and pressure interact in tufted capuchin monkeys (Sapajus [Cebus] apella) to influence performance on a DTMS task by varying the size of the possible stimulus pool across testing blocks. We also varied the amount of pressure within a testing block by training monkeys to associate a background color change with a more difficult, but more highly rewarded, trial, as we had done in previous work. In accordance with previous literature (Basile & Hampton, 2013), we found that performance greatly decreased when the possible stimulus pool was limited as compared to a large possible stimulus pool, likely because monkeys could not rely on passive familiarity memory to complete the task. However, we found no overall species tendency to fail under pressure in either the limited- or large-set conditions; instead, we found a surprising tendency to thrive under higher pressure. Taken together, our results further highlight the importance of considering DMTS task features when studying specific memory systems in non-human species and suggest that the DTMS task might not be the best paradigm for testing pressure effects without consideration of individual differences.