Global/local processing of hierarchical visual stimuli in a conflict–choice task by capuchin monkeys (Sapajus spp.)
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In the last two decades, comparative research has addressed the issue of how the global and local levels of structure of visual stimuli are processed by different species, using Navon-type hierarchical figures, i.e. smaller local elements that form larger global configurations. Determining whether or not the variety of procedures adopted to test different species with hierarchical figures are equivalent is of crucial importance to ensure comparability of results. Among non-human species, global/local processing has been extensively studied in tufted capuchin monkeys using matching-to-sample tasks with hierarchical patterns. Local dominance has emerged consistently in these New World primates. In the present study, we assessed capuchins’ processing of hierarchical stimuli with a method frequently adopted in studies of global/local processing in non-primate species: the conflict–choice task. Different from the matching-to-sample procedure, this task involved processing local and global information retained in long-term memory. Capuchins were trained to discriminate between consistent hierarchical stimuli (similar global and local shape) and then tested with inconsistent hierarchical stimuli (different global and local shapes). We found that capuchins preferred the hierarchical stimuli featuring the correct local elements rather than those with the correct global configuration. This finding confirms that capuchins’ local dominance, typically observed using matching-to-sample procedures, is also expressed as a local preference in the conflict–choice task. Our study adds to the growing body of comparative studies on visual grouping functions by demonstrating that the methods most frequently used in the literature on global/local processing produce analogous results irrespective of extent of the involvement of memory processes.
KeywordsVisual perception Global/local processing Hierarchical stimuli Long-term memory New World monkeys
We thank two anonymous reviewers for their thoughtful suggestions and constructive comments on the manuscript. We are also grateful to Tyrone Lucon Xiccato for his helpful statistical suggestions. We wish to thank Cinzia Trapanese, Francesca Cosentino and Adrian Soldati for help with data collection. We acknowledge Arianna Manciocco, Massimiliano Bianchi and Simone Catarinacci for help with animal management and for technical help with the apparatus. We also thank the Comune di Roma-Museo Civico Zoologia and the Fondazione Bioparco for hosting the Unit of Cognitive Primatology and the Primate Center.
Compliance with ethical standards
The research protocol for this study was approved by the Italian Health Ministry (Central Direction for the Veterinary Service, approvals n. 11/2011-C and n. DM132/2014-C to V. Truppa). All procedures were in accordance with the ethical standards of National Research Council of Italy, where the study was conducted.
Conflict of interest
The authors declare that they have no conflict of interest.
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