Symbol addition by monkeys provides evidence for normalized quantity coding

Proc Natl Acad Sci U S A. 2014 May 6;111(18):6822-7. doi: 10.1073/pnas.1404208111. Epub 2014 Apr 21.

Abstract

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.

Keywords: macaque; normalization; number sense; value coding.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Behavior, Animal / physiology
  • Choice Behavior / physiology
  • Learning / physiology*
  • Macaca mulatta / physiology*
  • Macaca mulatta / psychology*
  • Male
  • Mathematical Concepts
  • Models, Neurological
  • Models, Psychological
  • Reward