Visual categorization of natural and abstract items in forest monkeys and humans

A preference for novelty paradigm was used to investigate whether mangabeys (Lophocebus albigena), an arboreal non-human primate species, were able to discriminate and to categorize different visual stimuli belonging to natural (food items) and abstract (non-food items) categories. In a comparative perspective human subjects were tested with the same procedure and the same stimuli. Two out of four mangabeys and three out of the four humans showed significant preference for novelty when comparing food versus non-food items. Hence they discriminated between these two sets of items. The two mangabeys and one non-adult human subject sorted the food items in one category, showing no preference for novelty when comparing known and unknown food-items and different views of the same food items. In contrast the two adult human subjects who showed preference for novelty in the between-category, did not show preference for novelty when comparing known and unknown food-items but did show such a preference when comparing different views of the same food items. Compared to human performances, the results suggest that mangabeys are able to form at least a perceptual category of natural, ecologically relevant stimuli.