Training rhesus monkeys to perform the delayed matching-to-sample task on a touchscreen monitor

Abstract

The delayed matching-to-sample task (DMTS) is often used in animal working memory studies. In the classical DMTS paradigm, an animal is presented with a sample (three-dimensional object or image), and after some time—from seconds to minutes—with two stimuli, one of which is identical to the sample, while the other one is new. The animal gets reinforcement for choosing a stimulus identical to the sample. In non-human primate studies, researchers often use computerized versions of this test, with a touchscreen monitor for presenting stimuli and recording animal responses. However, these researchers do not normally discuss the process of teaching animals to perform this task on a touchscreen monitor, which is often a challenge for the experimenter. In this work, we describe the procedure for teaching rhesus monkeys (Macaca mulatta) to perform the DMTS task, using a computerized setup with a touchscreen monitor for stimulus presentation (geometric shapes of different colours). To teach monkeys, we used a training version of the task, where the sample is not just replaced by stimuli for matching, but shifts in the direction of one of the positions of stimuli for matching. With this training version of the task, it took us only one experimental session to teach six male monkeys to perform the DMTS task with a moving stimulus. Furthermore, we gradually increased task complexity by increasing the number of samples simultaneously presented for memorisation. Five out of six monkeys learned the more complex version of the task with two samples and proceeded to performing the task with three samples. This procedure for teaching monkeys to perform the DMTS task with varying numbers of samples presented for memorisation will promote the use of sensor screens for this test instead of actual physical objects, which will expand the opportunities for cognitive research on monkeys.