Recursive sequence generation in monkeys, children, U.S. adults, and native Amazonians

Abstract

The question of what computational capacities, if any, differ between humans and nonhuman animals has been at the core of foundational debates in cognitive psychology, anthropology, linguistics, and animal behavior. The capacity to form nested hierarchical representations is hypothesized to be essential to uniquely human thought, but its origins in evolution, development, and culture are controversial. We used a nonlinguistic sequence generation task to test whether subjects generalize sequential groupings of items to a center-embedded, recursive structure. Children (3 to 5 years old), U.S. adults, and adults from a Bolivian indigenous group spontaneously induced recursive structures from ambiguous training data. In contrast, monkeys did so only with additional exposure. We quantify these patterns using a Bayesian mixture model over logically possible strategies. Our results show that recursive hierarchical strategies are robust in human thought, both early in development and across cultures, but the capacity itself is not unique to humans.

Chimpanzee histology and functional brain imaging show that the paracingulate sulcus is not human-specific

“…Implicit mentalizing abilities have been described in chimpanzees and macaques 77 , 78 , and are affected by reversible lesions of the ACC in macaques 78 . Recursive thinking and counterfactual manipulation of information to guide behavior have also been observed in macaques 75 , 79 . Counterfactual reasoning was also impacted by reversible lesions of the ACC in macaques 75 .…”

Sensitivity to geometric shape regularity in humans and baboons: A putative signature of human singularity

“…A great variety of non-exclusive hypotheses have been proposed to account for human singularity, including the emergence of evolved mechanisms for social competence (1), pedagogy (2), natural language (3,4), or recursive structures across multiple domains such as language, music and mathematics (5)(6)(7)(8). Unfortunately, few experimental paradigms, mostly in the domain of artificial grammar learning, afford a direct comparison of human and non-human primate behavior using the same methods (9)(10)(11)(12)(13)(14). Here, we present experimental investigations of the differences between humans and baboons in the domain of geometry, and more specifically, the visual perception of quadrilaterals such a square, a rectangle or a parallelogram.…”

Mental compression of spatial sequences in human working memory using numerical and geometrical primitives

“…A prominent hypothesis is that the capacity to represent embedded structures may be specific to the human species (Fitch, 2014;Hauser et al, 2002). Indeed, several comparative studies found that, while human and non-human primates exhibit similar performance in sequence processing whenever sequential relations, statistical properties or simple nonadjacent dependencies suffice to perform the task (Hauser et al, 2001;Milne et al, 2016Milne et al, , 2018Newport et al, 2004;Ravignani et al, 2013;Sonnweber et al, 2015;Wilson et al, 2013Wilson et al, , 2017, important differences are observed when the sequences involve embedding or recursion (Ferrigno et al, 2020;Fitch, 2004;Jiang et al, 2018;Wang et al, 2015). For instance, in a spatial motor task, although macaque monkeys could learn a supra-regular grammar and generalize it to novel sequences, they need a training period of thousands of trials to achieve the performance level that preschool children reach in only a few trials (Jiang et al, 2018).…”

“…Thus, although the acquisition of simple embedded sequences may not be out of reach of macaque monkeys (Ferrigno et al, 2020;Jiang et al, 2018), the difference between human and non-human primates may originate, at least in part, in human's ability to rapidly acquire complex sequential rules.…”

“…For instance, in a spatial motor task, although macaque monkeys could learn a supra-regular grammar and generalize it to novel sequences, they need a training period of thousands of trials to achieve the performance level that preschool children reach in only a few trials (Jiang et al, 2018). Thus, although the acquisition of simple embedded sequences may not be out of reach of macaque monkeys (Ferrigno et al, 2020; Jiang et al, 2018), the difference between human and non-human primates may originate, at least in part, in human’s ability to rapidly acquire complex sequential rules.…”