Implicit and explicit category learning by capuchin monkeys (Cebus apella)

J. David Smith*, Matthew J. Crossley, Joseph Boomer, Barbara A. Church, Michael J. Beran, F. Gregory Ashby

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

22 Citations (Scopus)


Current theories of human categorization differentiate an explicit, rule-based system of category learning from an implicit system that slowly associates regions of perceptual space with response outputs. The researchers extended this theoretical differentiation to the category learning of New World primates. Four capuchins (Cebus apella) learned categories of circular sine-wave gratings that varied in bar spatial frequency and orientation. The rule-based and information-integration tasks, respectively, had onedimensional and two-dimensional solutions. Capuchins, like humans, strongly dimensionalized the stimuli and learned the rule-based task more easily. The results strengthen the suggestion that nonhuman primates have some structural components of humans' capacity for explicit categorization, which in humans is linked to declarative cognition and consciousness. The results also strengthen the primate contrast to other vertebrate species that may lack the explicit system. Therefore, the results raise important questions about the origins of the explicit categorization system during cognitive evolution and about its overall phylogenetic distribution.

Original languageEnglish
Pages (from-to)294-304
Number of pages11
JournalJournal of Comparative Psychology
Issue number3
Publication statusPublished - Aug 2012
Externally publishedYes


  • explicit categorization
  • primate cognition
  • comparative cognition
  • category learning
  • capuchin monkeys


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