Povinelli, D. J., & Henley, T. (2020). More rope tricks reveal why more task variants will never lead to strong inferences about higher-order causal reasoning in chimpanzees. Animal Behavior and Cognition, 7(3), 392-418. doi: https://doi.org/10.26451/abc.07.03.08.2020

When chimpanzees (and other animals) use tools to pound, crack open, retrieve, soak up, pry apart, probe into, and/or dig up other objects (just to name a few of the operations of which they are capable), are these actions modulated by higher-order, structural, role-based representations of , , , and so forth? We report a study that was designed to shed light on what chimpanzees understand about and between objects. We presented expert tool-using chimpanzees with very familiar objects (ropes) in a very familiar testing context (hooking and retrieving an object containing food). We investigated whether they could transfer the known operation (hooking and pulling) to two distinct setups involving ropes (a looped rope that could effectuate the transfer of force, and a draped length of rope that could not¾unless both ends were grasped at the same time). We show that first-order, perceptually-based relational reasoning is both necessary and sufficient to explain not only the impressive pattern of results we did obtain, but any possible pattern of results we could have obtained. If correct, any claim that higher-order reasoning is necessary to explain the results of such a test would, by definition, be false. More importantly, we show that this is not an idiosyncratic limitation of this experiment. Instead, we show that all experimental protocols claiming to assay higher-order reasoning in animals rest upon an extremely suspect, and ultimately unprincipled, titration. Specifically, researchers implicitly assume that the tasks are perceptually similar enough to what their subjects have previously encountered to allow them make sense of the problem, but perceptually different enough that the subjects must (somehow) rely upon higher-order reasoning to navigate their way through it. We show why such assumptions are false.

Causal cognition, Chimpanzees, Tool use, Physical cognition