Strong evidence indicates that non-human primates possess a numerical representation system, but the inherent nature of that system is still debated. Two cognitive mechanisms have been proposed to account for non-human primate numerical performance: (1) a discrete object-file system limited to quantities <4, and (2) an analog system which represents quantities comparatively but is limited by the ratio between two quantities. To test the underlying nature of non-human primate quantification, we asked eight experiment-naive olive baboons (Papio anubis) to discriminate between number pairs containing small (<4), large (>4), or span (small vs. large) numbers of food items presented simultaneously or sequentially. The prediction from the object-file hypothesis is that baboons will only accurately choose the larger quantity in small pairs, but not large or span pairs. Conversely, the analog system predicts that baboons will be successful with all numbers, and that success will be dependent on numerical ratio. We found that baboons successfully discriminated all pair types at above chance levels. In addition, performance significantly correlated with the ratio between the numerical values. Although performance was better for simultaneous trials than sequential trials, evidence favoring analog numerical representation emerged from both conditions, and was present even in the first exposure to number pairs. Together, these data favor the interpretation that a single, coherent analog representation system underlies spontaneous quantitative abilities in primates.
Keywords: numerosity, primates, baboons, object-file, analog magnitude
Citation: Barnard AM, Hughes KD, Gerhardt RR, DiVincenti L Jr, Bovee JM and Cantlon JF (2013) Inherently analog quantity representations in olive baboons (Papio anubis). Front. Psychol. 4:253. doi: 10.3389/fpsyg.2013.00253
Received: 01 August 2012; Accepted: 16 April 2013;
Published online: 02 May 2013.
Edited by:Michael Beran, Georgia State University, USA
Reviewed by:Stephen V. Shepherd, Princeton University, USA
Copyright: © 2013 Barnard, Hughes, Gerhardt, DiVincenti, Bovee and Cantlon. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.
*Correspondence: Jessica F. Cantlon, Department of Brain and Cognitive Sciences, University of Rochester, Meliora Hall, PO Box 270268, Rochester, NY 14627, USA. e-mail: firstname.lastname@example.org