Free-ranging rhesus monkeys spontaneously individuate and enumerate small numbers of non-solid portions

Abstract

Fundamental questions in cognitive science concern the origins and nature of the units that compose visual experience. Here, we investigate the capacity to individuate and store information about non-solid portions, asking in particular whether free-ranging rhesus monkeys (Macaca mulatta) quantify portions of a non-solid substance presented in discrete pouring actions. When presented with portions of carrot pieces poured from a cup into opaque boxes, rhesus picked the box with the greatest number of portions for comparisons of 1 vs. 2, 2 vs. 3, and 3 vs. 4, but not for comparisons of 4 vs. 5 and 3 vs. 6. Additional experiments indicate that rhesus based their decisions on both the number of portions and the total amount of food. These results show that the capacity to individuate non-solid portions is not unique to humans, and does not depend on structures of natural language. Further, the fact that rhesus' ability to represent non-solid portions is constrained by the same 4-item limit typically ascribed to the system of parallel individuation that operates over solid objects suggests that the visual system recruits common working memory processes for retaining information about solid objects and non-solid portions. We discuss our results with respect to theories of visual processing, as well as to the role that the human language faculty may have played in both the evolution and development of quantification.3

When quantity trumps number: discrimination experiments in cotton-top tamarins (Saguinus oedipus) and common marmosets (Callithrix jacchus)

“…Rhesus monkeys, on the other hand, appear to base their decision on number-when presented with one large apple slice and three apple slices equal in volume, rhesus prefer the container that received three slices. Although it remains untested whether rhesus can attend to total amount over number under these condition as do human infants, a recent study shows that rhesus attend to both number and total amount when presented with small numbers of non-solid collections (carrot pieces) that are poured from one container into another (Wood et al 2007). The fact that human infants and adults demonstrate a similar limit in a variety of tasks (Feigenson et al 2002;Luck and Vogel 1997;Pylyshyn and Storm 1988), again suggests continuity of this mechanism across ontogeny and phylogeny.…”

Perceptual consciousness overflows cognitive access

“…The same number (though decreased slightly for infants) shows up in a variety of experiments that track memory of ongoing events [63,64]. For example, if a monkey sees an experimenter ostentatiously place a small number of pieces of apple in one bucket, one at a time, and a small number in another bucket, again one at a time, when the experimenter withdraws, the monkey reliably goes to the bucket with more pieces if the numbers of pieces in both buckets are 4 or fewer [65,66]. However, if the number of pieces in one of the buckets exceeds 4, the monkey's choices are at chance level: for instance, in the case of 3 vs. 4, monkeys reliably pick 4, but in the case of 3 vs. 8, they choose randomly.…”

Evidence for a non-linguistic distinction between singular and plural sets in rhesus monkeys

“…If it is, then the signatures of PI should be found when small sets are presented one individual at a time, as in previous studies that document limits of PI in rhesus monkeys (Hauser & Carey, 2003;Hauser et al, 2000;Wood et al, 2008) and in human infants (Barner et al, 2007;Cheries et al, 2006;Feigenson & Carey, 2005;Feigenson et al, 2002). To explore this, we tested rhesus monkeys on the numerical comparisons of Experiment 1, but presented apples as independently moving objects that were hidden individually.…”

“…We adapted a forced-choice foraging paradigm that has provided evidence of PI representations in previous studies (Hauser et al, 2000;Wood et al, 2008) Subjects were allowed to choose one of two sets of apples that were hidden in two boxes. In previous studies, food objects were introduced into the boxes one at a time.…”

“…The PI system has a limited capacity, and permits the parallel representation of 3 (human infants) or 4 (adult humans and adult rhesus) individuals per set (Barner, Thalwitz, Wood, Yang, & Carey, 2007;Cheries, Wynn, & Scholl, 2006;Feigenson & Carey, 2003;Feigenson & Carey, 2005;Feigenson et al, 2004;Hauser & Carey, 2003;Hauser, Carey, & Hauser, 2000;Jiang, Olson, & Chun, 2000;Luck & Vogel, 1997;Pylyshyn, 2003;Vogel, Woodman, & Luck, 2001;Wood, Hauser, Glynn, & Barner, 2008; see also Uller, Jaeger, & Guidry, 2003, for evidence of a set-size limit in salamanders). The limits of PI are likely subject to individual differences (e.g., possibly due to different training histories; see Vogel et al, 2001) and may also be affected by contextual factors that interfere with PI representations (see Cheries et al, 2006).…”