Can nonhuman primates use tokens to represent and sum quantities?

Abstract

It is unclear whether nonhuman animals can use physical tokens to flexibly represent various quantities by combining token values. Previous studies showed that chimpanzees (Pan troglodytes) and a macaque (Macaca mulatta) were only partly successful in tests involving sets of different-looking food containers representing different food quantities, while some capuchin monkeys (Cebus apella) have shown greater success in tests involving sets of various concrete objects representing different food quantities. Some of the discrepancy in results between these studies may be attributed to the different methods employed. In an effort to reconcile these discrepancies, we presented two primates species, chimpanzees and capuchin monkeys, with two token tasks. The critical test in each task involved summing the value of multiple tokens of different types to make accurate quantity judgments. We found that, using either method, individuals of both species learned to associate individual tokens with specific quantities, as well as successfully compare individual tokens to one another or to sets of visible food items. However, regardless of method, only a few individuals exhibited the capacity to sum multiple tokens of different types and then use those summed values to make an optimal response. This suggests that flexible combination of symbolic stimuli in quantity judgments tasks is within the abilities of chimpanzees and capuchins but does not characterize the majority of individuals. Furthermore, the results suggest the need to carefully examine specific methodological details that may promote or hinder such possible representation.

Sequential responding and planning in capuchin monkeys (Cebus apella)

“…Capuchin monkeys often perform similarly as great apes and rhesus macaques in tests of physical cognition (Beran 2008; Beran et al 2008a, 2008b; D’Amato and Colombo 1988; Evans, Beran and Addessi 2010; Evans and Westergaard 2004; Flemming 2011; Judge, Evans and Vyas 2005; Kennedy and Fragaszy 2008; McGonigle, Chalmers and Dickinson 2003; Poti et al 2010; Wright and Katz 2006; Yocum and Boysen 2010). However, this New World monkey species has also demonstrated significant differences from other species in higher-order cognitive processes such as memory monitoring and metacognition (e.g., Beran et al 2009; Fujita 2009).…”

“…In many respects, they are considered the “poor person’s chimpanzee” with cognitive skills closely in line with those shown by apes and Old World monkey species in a variety of tasks including, but not limited to, tests of quantity judgment, self control, tool use, concept formation, analogical reasoning, and spatial representations (Beran 2008; Beran et al 2008a, 2008b; D’Amato and Colombo 1988; Evans, Beran and Addessi 2010; Evans and Westergaard 2004; Flemming 2011; Judge, Evans and Vyas 2005; Kennedy and Fragaszy 2008; McGonigle, Chalmers and Dickinson 2003; Poti et al 2010; Wright and Katz 2006; Yocum and Boysen 2010). But, recent research has indicated that capuchin monkeys lack one capacity that both apes and Old World monkeys (and perhaps even other species) have been argued to possess: metacognition.…”

Chimpanzees (Pan troglodytes) transfer tokens repeatedly with a partner to accumulate rewards in a self-control task

“…In an earlier series of studies, one chimpanzee (Sherman) had experience requesting and exchanging tools and food items with a conspecific using the lexigram system (see Savage-Rumbaugh et al 1978a, 1978b). All four chimpanzees also have been tested previously in tasks involving tokens representing different quantities of foods as well as one task involving the choice between immediately consumable rewards and lexigram tokens exchangeable later for better rewards (Beran and Evans 2012; Beran et al 2011; Evans et al 2010). …”

Language‐Trained Chimpanzees (Pan troglodytes) Delay Gratification by Choosing Token Exchange Over Immediate Reward Consumption

“…Beran, ; Beran et al, ; Evans & Beran, ]. The chimpanzees had also participated in multiple previous studies involving token exchange [Beran et al, ; Brosnan & Beran, ; Evans et al, , ].…”