Shared System for Ordering Small and Large Numbers in Monkeys and Humans

Abstract

There is increasing evidence that animals share with adult humans and perhaps human infants a system for representing objective number as psychological magnitudes that are an analogue of the quantities they represent. Here we show that rhesus monkeys can extend a numerical rule learned with the values 1 through 9 to the values 10, 15, 20, and 30, which suggests that there is no upper limit on a monkey's numerical capacity. Instead, throughout the numerical range tested, both accuracy and latency in ordering two numerical values were systematically controlled by the ratio of the values compared. In a second experiment, we directly compared humans' and monkeys' performance in the same ordinal comparison task. The qualitative and quantitative similarity in their performance provides the strongest evidence to date of a single nonverbal, evolutionarily primitive mechanism for representing and comparing numerical values.

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

“…However, a wide range of non-human primate species certainly can deploy them for sets this size (Beran, 2007;Beran & Beran, 2004;Brannon & Terrace, 1998, 2000Call, 2000;Cantlon & Brannon, 2006, 2007Dehaene, 1997;Lewis, Jaffe, & Brannon, 2005). There were several significant differences between our study and these previous reports.…”

“…The ratio-limit signature of AM representations has been found in human adults, infants, rats, and various other species (Barth, Kanwisher, & Spelke, 2003;Brannon, Abbott, & Lutz, 2004;Brannon & Terrace, 1998;Brannon & Terrace, 2000;Cantlon & Brannon, 2006;Cordes, Gelman, & Gallistel, 2002;Gallistel, 1990;McCrink & Wynn, 2004;Platt & Johnson, 1971;Shettleworth, 1998;Whalen, Gallistel, & Gelman, 1999;Xu, 2003;Xu & Spelke, 2000;Xu, Spelke, & Goddard, 2005). Several studies document AM representations in rhesus monkeys (Brannon & Terrace, 1998, 2000Cantlon & Brannon, 2006;Flombaum, Junge, & Hauser, 2005). For example, looking-time studies reveal a capacity to discriminate 4 objects from 8, but a failure to discriminate comparisons where the ratio between sets is smaller, such as 4 vs. 6 (Flombaum et al, 2005).…”

“…We do not claim that AM is a ''large number'' system and PI a ''small number'' system. Experiments from various species make it clear that AM is defined for small sets as well as large sets (e.g., Beran, 2007;Beran & Beran, 2004;Brannon & Terrace, 1998, 2000Call, 2000;Cantlon & Brannon, 2006;Cantlon & Brannon, 2007;Dehaene, 1997;Lewis, Jaffe, & Brannon, 2005;vanMarle, Aw, McCrink, & Santos, 2006;vanMarle & Wynn, 2003). 3 Our interpretation of the literature, instead, is that there are two different ways of representing numerical information, distinguishable by their distinctive processing signatures (see Feigenson et al, 2004, for review).…”

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

“…First, animals can discriminate between approximate numerosities via a system of analog magnitudes, in which performance is limited by the ratio between the quantities independent of absolute value. Cantlon and Brannon (2006), for example, demonstrated that in operantly trained rhesus monkeys, ratio determined numerical discrimination between quantities ranging from 1 to 30 items. Human infants and adults also represent large approximate numbers and show similar signature ratio limits (Barth et al 2003;Cantlon and Brannon 2006;Xu and Spelke 2000), suggesting a common system of numerical representation.…”

Exploring the numerical mind by eye-tracking: a special issue

“…Wynn (1992) showed that infants look longer at a single doll that is revealed from behind an occluder when they previously observed an addition scenario (i.e., a second doll was added to an initial single doll, thus the expected solution would be ''two'') than when they previously observed a subtraction scenario (i.e., one doll was subtracted from a pair of dolls, thus the expected solution would be ''one''). Moreover, the time infants (and also monkeys) spend looking at visual arrays follows Weber's Law (Cantlon & Brannon, 2006;Libertus & Brannon, 2010). Furthermore, newborn infants preferentially look at arrays of visually presented objects that numerically match the number of auditory phonemes to which they have previously been familiarized (Izard, Sann, Spelke, & Streri, 2009).…”