Horses (Equus caballus) select the greater of two quantities in small numerical contrasts

Abstract

The ability to select the greater numerosity over another in small sets seems to stem from the calculation of which set contains more, and has been taken as evidence of a primordial representation at the roots of the primate numerical system. We tested 56 horses (Equus caballus) in a paradigm previously used with human infants and nonhuman primates. Horses saw two quantities paired in contrasts-2 versus 1, 3 versus 2, 6 versus 4 and a control for volume, 2 versus 1 big-and had to make a choice by snout touching the container holding the numerosity selected. The horses spontaneously selected the greater of the two quantities when the numerosities were small. These results add to evidence showing spontaneous quantity assessment in a variety of species.

Quantity discrimination in salamanders

“…While data from animals in their natural environment are restricted to a few studies, e.g. lions (McComb, 1994), chimpanzees (Wilson et al, 2001) and coots (Lyon, 2003), a wealth of evidence comes from laboratory experiments, which characterize spontaneously available numerical abilities mainly in human infants (Uller et al, 1999;Xu and Spelke, 2000;Feigenson and Carey, 2003;Xu et al, 2005) and non-human primates (Hauser et al, 2003;Flombaum et al, 2005;Lewis et al, 2005;Santos et al, 2005), but also in horses (Uller and Lewis, 2009), birds (Hunt et al, 2008;Rugani et al, 2009), fish (Agrillo et al, 2007;Agrillo et al, 2008), salamanders (Uller et al, 2003) and insects (Carazo et al, 2009;Gross et al, 2009). Results suggest two systems: one system for small sets (≤4) that is precise but limited, as it works by keeping track of individual entities; and one system for larger sets that is independent of absolute set size, works on imprecise analogue magnitudes and hence is subject to Weber's Law, i.e.…”

Numerical assessment in the wild: insights from social carnivores

“…Researchers in these fields have found that the ability to discriminate between different numbers of objects appears to be a foundational cognitive ability and have documented this ability in numerous species across the Animal Kingdom. For example, quantity discrimination has been demonstrated experimentally in several species of fish [5,11,[19][20][21], amphibians [8,22,23], birds [18,[24][25][26][27][28][29][30][31][32][33][34][35], mammals [9,[36][37][38][39][40][41], primates [42][43][44][45], human infants [46][47][48][49] and even some invertebrates [50][51][52]. The only study testing quantity discrimination in a reptile found that although ruin lizards (Podarcis sicula) do spontaneously select the larger quantity of food, they do not spontaneously select the option with a higher number of food items [53].…”

Evolution of working memory

“…Similar tests have been conducted with horses, showing that they can distinguish between a bucket into which two apples have been placed and one containing three apples and fail to distinguish between buckets containing four apples and six apples, respectively (34). In such experiments, it seems unlikely that the animals could benefit from chunking because all of the items are of the same type.…”