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Kerry E. Jordan, Evan L. MacLean, Elizabeth M. Brannon; Monkeys match sequentially presented sets with simultaneously presented arrays based on numerosity. Journal of Vision 2006;6(6):186. doi: 10.1167/6.6.186.
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© ARVO (1962-2015); The Authors (2016-present)
Recent studies demonstrate profound similarities between the nonverbal number representations of humans and nonhuman primates. For instance, monkeys' accuracy and reaction time in making numerical judgments are modulated by ratio (e.g., Cantlon & Brannon, in press; Jordan and Brannon, submitted). Monkeys also detect numerical correspondences between sets presented in different formats or sensory modalities (e.g., Hauser et al., 2003; Jordan et al., 2005); however, these studies have tested untrained animals in tasks that assess spontaneous looking or orienting to stimuli. It remains unknown whether monkeys can make explicit matches based on numerical correspondences across different stimulus formats or modalities. As a first step toward answering this question, we trained two rhesus monkeys to numerically match visual stimuli presented in different formats on a touch-sensitive monitor in a match-to-sample task. Samples were sequences of sequentially presented visual elements, whereas the two choice stimuli were arrays of simultaneously presented elements. The choices were presented after the last element in the sample array, and correct responses were rewarded with juice. Results indicate that choices were based on number regardless of other varying parameters such as total sample sequence duration, rate, individual sample element duration, inter-element interval, cumulative surface area, and perimeter. Accuracy was also modulated by the ratio between the sample and the distracter numerosities. Results thus show that monkeys can explicitly match number across presentation format in the visual modality. Future studies will assess monkeys' abilities to explicitly match number across sensory modalities.
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