ABC 2018, 5(1) 103-117 Animal Behavior and Cognition https://doi.org/10.26451/abc.05.01.08.2018 ©Attribution 3.0 Unported (CC BY 3.0) Gorillas (Gorilla gorilla gorilla) Fail to Learn Abstract Cues of Differential Outcomes in a Novel Cognitive Bias Test Molly C. McGuire and Jennifer Vonk* Oakland University, Department of Psychology, Rochester, MI, USA *Corresponding author (Email: vonk@oakland.edu) Citation – 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 Abstract – 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. Keywords – Gorillas, Affect, Cognitive bias, Quantity, Conditional discrimination Cognitive bias in animals (as well as humans) can be described as a bias in cognitive processing due to changes in affective state. More specifically, the tendency to interpret neutral or ambiguous stimuli in a negative manner is considered pessimism, whereas the tendency to interpret neutral or ambiguous stimuli in a positive manner is considered optimism. Humans that display a negative cognitive bias are more likely to develop and maintain mood disorders such as anxiety and depression (Hallion & Ruscio, 2011). Therefore, cognitive bias tasks may serve an important role in assessing psychological well-being. In humans, cognitive bias is often assessed using verbal exercises. Participants given ambiguous sentences (e.g., “They discussed the priest’s strong convictions”) are asked to make various judgements about the meaning of those sentences; for example, to choose between a positive interpretat ion, “They discussed the priest’s strong beliefs” or a negative interpretation, “They discussed the priest’s criminal record” (Hallion & Ruscio, 2011, p. 2). These verbal exercises have been used to assess existing cognitive biases and to manipulate cognitive biases. By manipulating the valence of the primer sentences that participants read, researchers have induced negative or positive cognitive biases in healthy populations, causing the participants to interpret ambiguous statements as either threatening or benign (Hallion & Ruscio, 2011; Mathews et al., 2000). Cognitive bias tasks such as these have even been developed into a form of cognitive bias modification therapy as a way of treating maladaptive cognitive biases in unhealthy populations (Hallion & Ruscio, 2011). Clearly, cognitive bias assessments are a useful tool in the measurement and manipulation of human biases.