This study involved twelve adult Black-handed spider monkeys, with ages ranging from 4 to 20 years. The monkeys, a mix of both free-ranging and captive, were housed at a field station of the Universidad Veracruzana in Mexico. The captive monkeys were accustomed to participating in studies. and the free-ranging ones were also familiar with human interactions and adapted well to the study environment. Data were collected from May to October 2022.
Our test apparatus comprised a metal bar fitted with two boxes, each having a laminated card of either black or white color. Each box had the potential to contain a food reward. The main task for the monkeys was to understand and learn which color (black or white) was associated with a food reward. Once the monkeys had learned this association, we ‘reversed’ the reward-color link. If black was previously the rewarded color, it was now white, and vice versa. The monkeys’ adaptability to this reversal was a primary focus of our assessment.
We used the same apparatus as in Experiment 1, but with a slight modification: the boxes were fitted with cards that exhibited different black-and-white shapes instead of solid colors. The monkeys were tested on their capability to associate specific shapes with a food reward and we monitored how quickly they could learn these associations across a set of 20 different and ordered shape pairs.
For this test, we used the same apparatus but fitted the boxes with cards displaying the first pair of shapes used in the learning-set formation task: after a 12-week gap, we aimed to assess whether the monkeys were capable of remembering the first shape-reward association in a single-trial test.