Development of a standard test to assess negative reinforcement learning in horses

https://doi.org/10.1016/j.applanim.2015.05.005Get rights and content

Highlights

  • Negative reinforcement learning was evaluated in a pressure-release task using an algometer.

  • Force required for a correct response decreased with repetition on the first day.

  • More force was generally required on the right compared to the left side of the horse.

  • Horses appear unable to transfer learned responses to a tactile cue from one side to the other.

Abstract

Most horses are trained by negative reinforcement. Currently, however, no standardised test for evaluating horses’ negative reinforcement learning ability is available. The aim of this study was to develop an objective test to investigate negative reinforcement learning in horses. Twenty-four Icelandic horses (3 years old) were included in this study. The horses were tested in a pressure-release task on three separate days with 10, 7 and 5 trials on each side, respectively. Each trial consisted of pressure being applied on the hindquarter with an algometer. The force of the pressure was increased until the horse moved laterally away from the point of pressure. There was a significant decrease in required force over trials on the first test day (P < 0.001), but not the second and third day. The intercepts on days 2 and 3 differed significantly from day 1 (P < 0.001), but not each other. Significantly stronger force was required on the right side compared to the left (P < 0.001), but there was no difference between first and second side tested (P = 0.56). Individual performance was evaluated by median-force and the change in force over trials on the first test day. These two measures may explain different characteristics of negative reinforcement learning. In conclusion, this study presents a novel, standardised test for evaluating negative reinforcement learning ability in horses.

Introduction

The value of domestic horses is dependent on their ability to learn the various tasks set by humans. The horse sector would therefore benefit from the development of standardised methods to measure learning in horses. Equine learning ability has been investigated mainly in tests based on positive reinforcement (Nicol, 2002), including visual discrimination tasks (Gabor and Gerken, 2010), target touching and following (Christensen et al., 2012, Valenchon et al., 2013) and detour learning (Baragli et al., 2011). In contrast, most horse training is based on negative reinforcement (McGreevy and McLean, 2010). Studies have shown that horses’ general learning ability cannot be evaluated based on performance in one test alone (Visser et al., 2003, Wolff and Hausberger, 1996). Rather, learning ability appears to be specific to the learning mechanism targeted, thus, performance in a test based on positive reinforcement does not necessarily predict performance in a negatively reinforced test. Consequently, investigations of horses’ ability to learn through negative reinforcement and factors influencing this ability require a test based on negative reinforcement.

Negative reinforcement is an instrumental learning mechanism, where the instrumental response turns off an aversive stimulus (Domjan, 2010). By turning off the aversive stimulus the animal is rewarded for the instrumental response and will be more likely to perform the same response when it encounters the same aversive stimulus in the future.

In horse training the aversive stimulus is often some kind of pressure to the body of the horse, such as leg pressure or rein tension. The force of the pressure is increased until the correct response is obtained and rewarded by release of the pressure (McGreevy and McLean, 2010). Currently, no standardised test for evaluating equine learning ability through negative reinforcement is available, and the present study aimed to develop an objective test in this area. Learning was evaluated in a pressure-release task, where the pressure was applied in a standardised manner by an algometer, which also measured the force of the required pressure.

We hypothesised that the force required for the horse to respond correctly would decrease with repetition within as well as between days.

Section snippets

Materials and methods

The experiment was conducted during November 2012 and conformed to the Guidelines for ethical treatment of animals in applied animal behaviour and welfare research [http://www.applied-ethology.org/ethical_guidelines.html].

Results

The applied force ranged from 0.04 N to the actuator limit of 30 N (median [25; 75% quartile]: 17.83 N [8.22; 30]). There was one instance of what could have been interpreted as a threat to kick, but generally the horses tried to avoid the pressure by moving sideways or forward or backwards, the two latter being prohibited by the handler. Some horses moved only one leg in response to the pressure, whereas others took several steps sideways; both types of response were rewarded. The horses had

Discussion

The results confirmed our main hypothesis. There was a significant decrease in force through the trials within the first day and the regression intercept was significantly higher on the first day compared to the second and third day. This indicates that the horses learned the task through negative reinforcement. Learning occurred primarily on the first day whereas the lower intercept on day 2 compared to day 1 indicates that the horses remembered the task. Hence, we present a novel,

Acknowledgements

We would like to thank the horse owners for kindly allowing us to use their horses; Anna Feldberg Marsbøll and Maria Vilain Rørvang for help with the experiments. This study was funded by The Independent Danish Research Council|Technology and Production (grant no. 11-107010) and The Graduate School of Science and Technology, Aarhus University.

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