McGuire, M.C., & Vonk, J. (2018). Gorillas (Gorilla gorilla gorilla) fail to learn abstract cues of differential outcomes in a novel cognitive bias test. Animal Behavior and Cognition, 5(1), 103-117. https://doi.org/10.26451/abc.05.01.08.2018

In order to assess mood state in three male western lowland gorillas housed in a bachelor group, we developed a novel version of a cognitive bias task. The background color of a touchscreen presented a conditional ‘if, then…” rule relating to outcomes involving differential amounts of food rewards. The gorillas struggled to reach a criterion of 80% responding required for testing. In follow-up experiments, we assessed whether the gorillas did in fact prefer three pieces of food to one piece of food when presented with images of food quantities and actual food quantities. Gorillas did not learn to select the stimulus that indicated three food items over one food item when we used images of actual quantities of the rewarded food but they did prefer three actual pieces of food. Thus, like other primates, gorillas may respond differently to quantities of edible and inedible items. In addition, they may struggle with learning conditional discriminations when cues to differential responses and outcomes are arbitrary rather than intuitively connected. These studies highlight the importance of methodology when devising tests to assess cognition or affect in nonhuman primates.

Gorillas, Affect, Cognitive bias, Quantity, Conditional discrimination