Trained Quantity Abilities in Horses (Equus caballus): A Preliminary Investigation

Abstract

Once believed to be a human prerogative, the capacity to discriminate between quantities now has also been reported in several vertebrates. To date, only two studies investigated numerical abilities in horses (Equus caballus) but reported contrasting data. To assess whether horses can be trained to discriminate between quantities, I have set up a new experimental protocol using operant conditioning. One adult female was trained to discriminate between 1 and 4 (Test 1) in three different conditions: non-controlled continuous variables (numerical and continuous quantities that co-vary with number are simultaneously available), 50% controlled continuous variables (intermediate condition), and 100% controlled continuous variables (only numerical information available). The subject learned the discrimination in all conditions, showing the capacity to process numerical information. When presented with a higher numerical ratio (2 vs. 4, Test 2), the subject still discriminated between the quantities but its performance was statistically significant only in the non-controlled condition, suggesting that the subject used multiple cues in presence of a more difficult discrimination. On the whole, the results here reported encourage the use of this experimental protocol as a valid tool to investigate the capacity to process numerical and continuous quantities in horses in future research.

Susceptibility to Size Visual Illusions in a Non-Primate Mammal (Equus caballus)

“…There are multiple evidences that horses exhibit quantificational abilities. Horses can discriminate the larger group of food items [19] or the larger set of dots in a bi-dimensional figure [20]. Also, they are capable of discriminating between continuous quantities.…”

Use of ordinal information by fish

“…The numerical skill involved in the above mentioned examples is commonly called ‘relative numerosity judgment 6 7 and consists in the capacity to discriminate which groups of objects are less and more numerous. Such a capacity has been described in species as diverse as chimpanzees, Pan troglodytes 8 , rhesus monkeys, Macaca mulatta 9 , dogs, Canis lupus familiaris 10 , horses, Equus caballus 11 , parrots, Psittacus erithacus 12 , chicks, Gallus gallus 13 , and guppies, Poecilia reticulata 14 .…”

Advances in Animal Cognition

“…However, quantity abilities had not been extensively studied in equines, or hoofstock of any kind. Petrazzini [5] developed a novel method to investigate quantity judgements in horses. This method can be adapted to study a variety of cognitive capacities, which is an important development considering that little is known about cognition in horses, despite the fact that they are readily available and have been bred to work closely with humans.…”

“…There is still much work to be done testing domestic species, which can be accessed more readily. The horse tested by Petrazzini [5] for example, resided in a private riding stable.…”

“…This Special Issue presents a series of papers that embody the innovation and breadth embraced by scientists currently investigating animal cognition. Papers are presented on species ranging from bumblebees [2], to North Island robins [3], Jamaican fruit bats [4], domestic horses [5], sun bears [6], and non-human primates [7,8,9,10,11]. The research reported in this issue was conducted in a range of wild and captive environments, including laboratories, zoos, and conservation organizations.…”