Monkeys (Macaca Mulatta and Cebus Apella) and Human Adults and Children (Homo Sapiens) Compare Subsets of Moving Stimuli Based on Numerosity

Allison Schwartz,Michael J Beran,Natasha Schultz,Scott Decker

doi:10.3389/fpsyg.2011.00061

Abstract

Two monkey species (Macaca mulatta and Cebus apella) and human children and adults judged the numerousness of two subsets of moving stimuli on a computer screen. Two sets of colored dots that varied in number and size were intermixed in an array in which all dots moved in random directions and speeds. Participants had to indicate which dot color was more numerous within the array. All species performed at high and comparable levels, including on trials in which the subset with the larger number of items had a smaller total area of coloration. This indicated a similarity across species to use the number of items in the subsets, and not dimensions such as area or volume, to guide decision making. Discrimination performance was constrained by the ratio between the subsets, consistent with other reports of numerousness judgments of stationary stimuli. These results indicate a similarity in numerical estimation ability for moving stimuli across primate species, and this capacity may be necessary for naturally occurring experiences in which moving stimuli must be summed.

Highlights

Animals show an impressive collection of quantitative abilities
Even looking at only the first 100 trials, 7 of 11 monkeys were significantly above chance (p < 0.05, binomial test), and this number of trials matches the number performed by adult humans
All groups of participants performed at high levels in the experiment. They distinguished which of two sets of moving stimuli was more numerous

Summary

Introduction

Animals show an impressive collection of quantitative abilities. When presented with stimuli in a variety of formats, they can quantify and in some cases even enumerate those stimuli. Some animals show counting-like abilities as they label or create sets to match a cardinal value (e.g., Matsuzawa, 1985; Capaldi and Miller, 1988; Boysen and Berntson, 1989; Pepperberg, 1994, 2006; Boysen et al, 1995; Beran and Rumbaugh, 2001; Xia et al, 2001; Roberts et al, 2002; Tomonaga and Matsuzawa, 2002). A number of species have shown successful performance including great apes (Boysen and Berntson, 1995; Boysen et al, 1999; Anderson et al, 2005; Hanus and Call, 2007), monkeys (Thomas and Chase, 1980; Brannon and Terrace, 2000; Judge et al, 2005; Santos et al, 2005; Brannon et al, 2006; Cantlon and Brannon, 2006; Beran, 2007; Addessi et al, 2008; Evans et al, 2009), pigeons (Roberts and Mitchell, 1994; Emmerton et al, 1997; Emmerton, 1998), dolphins (Kilian et al, 2003; Jaakkola et al, 2005), parrots (Pepperberg, 2006; Aïn et al, 2009), horses (Uller and Lewis, 2009), dogs (Ward and Smuts, 2007), voles (Ferkin et al, 2005), fish (Dadda et al, 2009), and salamanders (Uller et al, 2003)

Methods

Results

Conclusion