Symbol addition by monkeys provides evidence for normalized quantity coding.

Bibliographic Collection: 
Publication Type: Journal Article
Authors: Livingstone, Margaret S; Pettine, Warren W; Srihasam, Krishna; Moore, Brandon; Morocz, Istvan A; Lee, Daeyeol
Year of Publication: 2014
Journal: Proc Natl Acad Sci U S A
Volume: 111
Issue: 18
Pagination: 6822-7
Date Published: 2014 May 6
Publication Language: eng
ISSN: 1091-6490
Keywords: Animals, Behavior, Animal, Choice Behavior, Learning, Macaca mulatta, Male, Mathematical Concepts, Models, Neurological, Models, Psychological, Reward

Weber's law can be explained either by a compressive scaling of sensory response with stimulus magnitude or by a proportional scaling of response variability. These two mechanisms can be distinguished by asking how quantities are added or subtracted. We trained Rhesus monkeys to associate 26 distinct symbols with 0-25 drops of reward, and then tested how they combine, or add, symbolically represented reward magnitude. We found that they could combine symbolically represented magnitudes, and they transferred this ability to a novel symbol set, indicating that they were performing a calculation, not just memorizing the value of each combination. The way they combined pairs of symbols indicated neither a linear nor a compressed scale, but rather a dynamically shifting, relative scaling.

DOI: 10.1073/pnas.1404208111
Alternate Journal: Proc. Natl. Acad. Sci. U.S.A.