Horses (Equus caballus) select the greater of two quantities in small numerical contrasts
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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.
KeywordsQuantity representation Horses Number discrimination
We would like to thank Battleswick Farm (Theresa Redding), Bull Lane Livery (Sue Adamson), Brook Farm Stables (Jo Holland), Colchester Garrison Saddle Club (Julie Doggett), Park Stables (Linda Matthews), Pitchbury Farm (Peggy Kendrew) and Writtle Agricultural College (James Ballentine and Karen Rhimes) for having kindly agreed to the testing at their establishments. We thank Soizic le Courtois and Helene Houte for assistance with the testing. We also thank Susan Carey and Simon Fitzpatrick for useful comments on a previous version of this manuscript, and three anonymous reviewers for their insightful comments. The experiments described here comply with the current local laws and all institutional guidelines on the ethical use of animals and the legal requirements of the United Kingdom.
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