Comparing Geometric Shape Representations in Humans and Baboons: A Language of Thought Perspective

In various cultures, across history and at many different spatial scales, humans produce a rich variety of geometric shapes. Recent work has put forward a concrete proposition for a Language of Thought (LoT) underlying the mental representation of geometric shapes in contemporary humans. Initial experiments, based on a comparison of baboon and human performance in an intruder task, suggested that this ability could be unique to humans. Here, to deepen our understanding of the evolutionary origins of geometric representations, we compared humans and baboons (Papio papio) in a delayed geometric match-to-sample task with a broad array of shapes. Crucially, the presentation speed was manipulated so that, on slow-paced trials, animals were given more time to understand the shapes. The shapes were sampled from our proposed LoT and spanned a range of predicted geometric complexity under that model. Although the overall pattern of behavior was still strikingly different in humans and baboons, when presentations were slower, we did find a small contribution of the LoT representations in baboons, though weaker than in humans. In both species, longer looking time increased the effect of the LoT-based predictor. While humans used the ability to self-pace to modulate their looking time, thus benefiting from longer exposure times for more complex shapes and rendering this geometric complexity effect visible, baboons did not.