Production of Supra-regular Spatial Sequences by Macaque Monkeys

• Published in: Current biology 2018-06, Vol.28 (12), p.1851-1859.e4
• Main Authors: Jiang, Xinjian, Long, Tenghai, Cao, Weicong, Li, Junru, Dehaene, Stanislas, Wang, Liping
• Format: Article
• Language: English
• Subjects: abstract rule; Animals; center-embedded structure; Child; Child, Preschool; China; comparative; Female; hierarchical sequence; human uniqueness; Humans; language; Learning; Linguistics; Macaca mulatta - psychology; macaque monkey; Male; Memory; push-down stack; sequence learning; supra-regular grammar
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2018.04.047

Understanding and producing embedded sequences in language, music, or mathematics, is a central characteristic of our species. These domains are hypothesized to involve a human-specific competence for supra-regular grammars, which can generate embedded sequences that go beyond the regular sequences engendered by finite-state automata. However, is this capacity truly unique to humans? Using a production task, we show that macaque monkeys can be trained to produce time-symmetrical embedded spatial sequences whose formal description requires supra-regular grammars or, equivalently, a push-down stack automaton. Monkeys spontaneously generalized the learned grammar to novel sequences, including longer ones, and could generate hierarchical sequences formed by an embedding of two levels of abstract rules. Compared to monkeys, however, preschool children learned the grammars much faster using a chunking strategy. While supra-regular grammars are accessible to nonhuman primates through extensive training, human uniqueness may lie in the speed and learning strategy with which they are acquired. •Monkeys can flexibly reproduce a spatial sequence in forward or mirror order•Monkeys generalize the supra-regular mirror grammar to novel sequences•Preschool children learn the mirror grammar much faster using a chunking strategy•Human uniqueness may lie in the speed and strategy for sequence learning Jiang, Long, et al. demonstrate that macaques can be trained to produce center-embedded spatial sequences. Preschool children quickly learn the grammar using chunking and geometric structure to compress the information. The human brain may possess additional computational devices to efficiently represent sequences during inductive learning.