Abstract
The present study investigated how stress affects instrumental learning performance in horses (Equus caballus) depending on the type of reinforcement. Horses were assigned to four groups (N = 15 per group); each group received training with negative or positive reinforcement in the presence or absence of stressors unrelated to the learning task. The instrumental learning task consisted of the horse entering one of two compartments at the appearance of a visual signal given by the experimenter. In the absence of stressors unrelated to the task, learning performance did not differ between negative and positive reinforcements. The presence of stressors unrelated to the task (exposure to novel and sudden stimuli) impaired learning performance. Interestingly, this learning deficit was smaller when the negative reinforcement was used. The negative reinforcement, considered as a stressor related to the task, could have counterbalanced the impact of the extrinsic stressor by focusing attention toward the learning task. In addition, learning performance appears to differ between certain dimensions of personality depending on the presence of stressors and the type of reinforcement. These results suggest that when negative reinforcement is used (i.e. stressor related to the task), the most fearful horses may be the best performers in the absence of stressors but the worst performers when stressors are present. On the contrary, when positive reinforcement is used, the most fearful horses appear to be consistently the worst performers, with and without exposure to stressors unrelated to the learning task. This study is the first to demonstrate in ungulates that stress affects learning performance differentially according to the type of reinforcement and in interaction with personality. It provides fundamental and applied perspectives in the understanding of the relationships between personality and training abilities.
Highlights
How stress affects learning processes is a major question in behavioural science but has been extensively studied in a restricted array of species, mainly primates and rodents
When stressors unrelated to the learning task were added, learning performance significantly decreased with positive reinforcement and tended to decrease with negative reinforcement (Dunn test positive reinforcements (PR) vs. PR+external stressors (ES): Ptrials to reach stage 1 = 0.03, Pstages reached = 0.04; Dunn test negative reinforcements (NR) vs. NR+ES: Ptrials to reach stage 1 = 0.06, Pstages reached = NS; Fig 3A and 3B)
The present study contributes to a better understanding of the influence of stress on learning performance by showing the importance of the nature of the stress and personality
Summary
How stress affects learning processes is a major question in behavioural science but has been extensively studied in a restricted array of species, mainly primates and rodents (synthesis: [1,2,3,4]). These studies aimed to determine whether stress affects cognitive performance and if it acts as either a stimulant or detriment for performance. One of the most common representations of this relationship is the well-known ‘Yerkes and Dodson law’ that has been encountered in various studies [1] It describes an inverted U-shaped relationship between an individual’s state of stress and performance in a cognitive task. On the opposite, when a stressor is unrelated to the cognitive task, the cognitive performance is more likely to be impaired by the individual’s state of stress
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