Competitive control of cognition in rhesus monkeys

The brain has evolved different approaches to solve problems, but the mechanisms that determine which approach to take remain unclear. One possibility is that control progresses from simpler processes, such as associative learning, to more complex ones, such as relational reasoning, when the simpler ones prove inadequate. Alternatively, control could be based on competition between the processes. To test between these possibilities, we posed the support problem to rhesus monkeys using a tool-use paradigm, in which subjects could pull an object (the tool) toward themselves to obtain an otherwise out-of-reach goal item. We initially provided one problem exemplar as a choice: for the correct option, a food item placed on the support tool; for the incorrect option, the food item placed off the tool. Perceptual cues were also correlated with outcome: e.g., red, triangular tool correct, blue, rectangular tool incorrect. Although the monkeys simply needed to touch the tool to register a response, they immediately pulled it, reflecting a relational reasoning process between themselves and another object (Rself-other), rather than an associative one between the arbitrary touch response and reward (Aresp-reward). Probe testing then showed that all four monkeys used a conjunction of perceptual features to select the correct option, reflecting an associative process between stimuli and reward (Astim-reward). We then added a second problem exemplar and subsequent testing revealed that the monkeys switched to using the on/off relationship, reflecting a relational reasoning process between two objects (Rother-other). Because behavior appeared to reflect Rself-other rather than Aresp-reward, and Astim-reward prior to Rother-other, our results suggest that cognitive processes are selected via competitive control dynamics.