Seen left, Ana Knighten (2020) demonstrates how we used both auditory and visual cues to train monkeys to find a treat in one of two cups. She demonstrates that we show visually and shake each cup in succession, and the cup with the treat is the one that shows a treat on top and sounds like it rattles with treats inside. We did this so that we could use either a visual or an auditory cue to represent presence or absence of a treat and could use those to test inclusion and exclusion logic used by monkeys.
Can monkeys reason? Many studies have shown a simple use of logic by many monkey species in that they will select a cup that has been shown to have a treat or sounds like it has a treat (inclusion), and they can use exclusion to guess when a cup does not appear to have a treat or has a noiseless sound, that the other cup must have the treat. Still, researchers have argued that the monkeys who select well may not use logic, but rather are just avoiding an empty cup and seeking reward (approach/avoidance hypothesis). We tested these ideas both with visual and auditory presence and absence cues when 2 cups were used, and we complicated things by increasing the number of cups to 4, using a barrier to block 2 of the cups from a trial, and offering 1 or 2 cues of inclusion or exclusion. The result? The monkey data fit predicted logical outcome probabilities better than simply eliminating empty cups and/or guessing. We are in the revision stages of trying to publish these data now (2022).
Read the published article on reasoning here (Neiworth, Knighten, & Leppink-Shands, 2023)
Citation: Neiworth, J. J., Knighten, A. D., & Leppink-Shands, C. (2023). Is inferential reasoning a distinctly human cognitive feature? Testing reasoning in cotton-top tamarins (Saguinus oedipus). Journal of Comparative Psychology. Advance online publication. https://doi.org/10.1037/com0000356
Click on it to view the poster below of analogical reasoning, Experiment 1, presented at Psychonomics in November of 2021.