Simple Discrimination and Matching-to-sample with Two-Dimensional Stimuli in Infant Capuchin Monkeys

Abstract

This study investigated the possibility of teaching repeated shifts of simple discrimination (RSSD) and identity matching to sample (IDMTS) using two-dimensional stimuli in two experimentally naive infant capuchin monkeys (Sapajus sp.; subjects M24 and M25). RSSD training occurred by alternating trials in which only one stimulus was presented (single stimulus trial) with trials in which two or more stimuli were presented simultaneously. The reinforcement probability was gradually reduced in single-stimulus trials, making this training gradually more similar to the IDMTS procedure. Fifty-nine sessions were conducted with subject M24, and 52 sessions were conducted with subject M25 until the criterion was reached. The subjects then underwent IDMTS training, beginning with two choices and gradually moving to four choices. Forty-eight sessions were conducted with M24, and 50 sessions were conducted with M25 until the criterion was reached. The results showed that infant capuchins can acquire these repertoires. The present results were compared to previous studies that used the same kind of task in adult capuchin monkeys and compared to data obtained in the same task using three-dimensional objects as stimuli in adult and infant capuchins.   Keywords: Simple discrimination; identity matching-to-sample; infant capuchin monkeys