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Proops, L., Walton, M., & McComb, K. (2010). The use of human-given cues by domestic horses, Equus caballus, during an object choice task. Anim. Behav., 79(6), 1205–1209.
Abstract: Selection pressures during domestication are thought to lead to an enhanced ability to use human-given cues. Horses fulfil a wide variety of roles for humans and have been domesticated for at least 5000 years but their ability to read human cues has not been widely studied. We tested the ability of 28 horses to attend to human-given cues in an object choice task. We included five different cues: distal sustained pointing, momentary tapping, marker placement, body orientation and gaze (head) alternation. Horses were able to use the pointing and marker placement cues spontaneously but not the tapping, body orientation and gaze alternation cues. The overall pattern of responding suggests that horses may use cues that provide stimulus enhancement at the time of choice and do not have an understanding of the communicative nature of the cues given. As such, their proficiency at this task appears to be inferior to that of domestic dogs, Canis lupus familiaris, but similar to that of domestic goats, Caprus hircus.
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Sankey, C., Richard-Yris, M. - A., Leroy, H., Henry, S., & Hausberger, M. (2010). Positive interactions lead to lasting positive memories in horses, Equus caballus. Anim. Behav., 79(4), 869–875.
Abstract: Social relationships are important in social species. These relationships, based on repeated interactions, define each partner's expectations during the following encounters. The creation of a relationship implies high social cognitive abilities which require that each partner is able to associate the positive or negative content of an interaction with a specific partner and to recall this association. In this study, we tested the effects of repeated interactions on the memory kept by 23 young horses about humans, after 6 and 8 months of separation. The association of a reward with a learning task in an interactional context induced positive reactions towards humans during training. It also increased contact and interest, not only just after training, but also several months later, despite no further interaction with humans. In addition, this ‘positive memory’ of humans extended to novel persons. Overall, positive reinforcement enhanced learning and memorization of the task itself. These findings suggest remarkable social cognitive abilities that can be transposed from intraspecific to interspecific social contexts.
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Schneider, G., & Krueger, K. (2012). Third-party interventions keep social partners from exchanging affiliative interactions with others. Anim. Behav., 83(2), 377–387.
Abstract: Third-party interventions are defined as the interruption of dyadic interactions by third animals through direct physical contact, interposing or threats. Previous studies focused on the analysis of interventions against agonistic encounters. However, there have been no evaluations of interventions against affiliative behaviours, particularly in relation to the intervening animal�s social relationships and its social and spatial position. Horses, Equus caballus, are an interesting model species, as interventions against affiliative interactions occur more frequently than against agonistic interactions. In this study, 64 feral horses displayed 67 interventions in affiliative interactions and eight interventions in agonistic interactions within the observation period. We analysed the interventions in affiliative encounters, and found that it was mainly higher-ranking females that intervened in the affiliative interactions of group mates in the stable horse harems. The intervening animals took an active part in affiliative and agonistic encounters within the group, but did not occupy particular social roles or spatial positions. They intervened in affiliative interactions in which group mates with which they had social bonds interacted with other members of the group. They targeted the nonbonded animal and approached the one with which they were socially bonded. We suggest some species use third-party interventions in affiliative interactions to prevent competition for preferred social interaction partners from escalating into more costly agonistic encounters.
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Austin, N. P., & Rogers, L. J. (2012). Limb preferences and lateralization of aggression, reactivity and vigilance in feral horses, Equus caballus. Anim. Behav., 83(1), 239–247.
Abstract: Observational field studies were conducted on two remote populations of feral horses in Australia to determine whether lateralization is a characteristic of Equus caballus as a species or results from handling by humans. Group 1 had been feral for two to five generations and Group 2 for 10–20 generations. In both groups, left-side biases were present during agonistic interactions and in reactivity and vigilance. Therefore, as in other vertebrates, the right hemisphere appears to be specialized to control agonistic behaviour and responses to potential threats. The leftwards bias was stronger in measures of behaviour involving more aggression and reactivity. Preferences to place one forelimb in front of the other during grazing were also determined. No population bias of forelimb preference was found, suggesting that such limb preferences present in domestic horses may be entrained. Since stronger individual limb preferences were found in immature than in adult feral horses, limb preference may be modified by maturation or experience in the natural habitat. Stronger limb preference was associated significantly with elevated attention to the environment but only in younger feral horses. No sex differences in lateralization were found. The findings are evidence that horses show visual lateralization, as in other vertebrates, not dependent on handling by humans. Limb preference during grazing, by contrast, does appear to depend on experience.
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Hanggi, E. B., & Ingersoll, J. F. (2009). Long-term memory for categories and concepts in horses (Equus caballus). Anim. Cogn., 13(3), 451–462.
Abstract: Three horses (Equus caballus) with a history of performing cognitive tasks including discrimination learning, categorization, and concept use were tested to evaluate their long-term memory (LTM) in three experiments. In addition, use of LCD multi-displays for stimulus presentation was incorporated into cognition testing protocol for the first time with horses. Experiment 1 tested LTM for discrimination learning that originally occurred 6 years earlier. Five sets of stimuli were used and the two horses tested showed no decrement in performance on four of the sets; however, both horses did score below chance on one set. Experiment 2 examined long-term categorization recall 10 years after horses had demonstrated the ability to make stimulus selections based on shared characteristics within a given category. The horse tested for LTM after the decade-long interval immediately and consistently applied the previously learned categorization rule to not only familiar but also novel sets of stimuli. Experiment 3 tested another horse for LTM for a relative size concept. This horse had originally demonstrated concept rule use in order to select stimuli based on their relative size to one another. More than 7 years later and without further training, this horse reliably applied the previously established size concept to both familiar and novel sets of stimuli. These findings are the first reports of long-term categorical and conceptual memory in horses and are consistent with observations of domestic and wild horses, which indicate that behavioral and ecological events may be remembered for long periods of time. These studies also demonstrate the adaptive nature of horses with regard to their ability to generalize over several different testing conditions.
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Krueger, K., & Heinze, J. (2008). Horse sense: social status of horses (Equus caballus) affects their likelihood of copying other horses` behavior. Anim. Cogn., 11(3), 431–439.
Abstract: Animals that live in stable social groups need to gather information on their own relative position in the group`s social hierarchy, either by directly threatening or challenging others, or in a less costly manner, by observing interactions among others. Such indirect inference of dominance relationships has previously been reported from primates, rats, and birds and fish. Here, we show that domestic horses, Equus caballus, are similarly capable of social cognition. Taking advantage of a specific “following behavior” that horses show towards humans in a riding arena, we investigated whether bystander horses adjust their response to an experimenter according to the observed interaction and their own dominance relationship with the horse whose reaction to the experimenter they had observed before. Horses copied the following behavior towards an experimenter after watching a dominant horse following, but did not follow after observing a subordinate horse or a horse from another social group doing so. The following behavior which horses show towards an experimenter therefore appears to be affected by the demonstrator`s behavior and social status relative to the observer.
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Maros, K., Gácsi, M., & Miklósi, Á. (2008). Comprehension of human pointing gestures in horses ( Equus caballus ). Anim. Cogn., 11(3), 457–466.
Abstract: Abstract Twenty domestic horses (Equus caballus) were tested for their ability to rely on different human gesticular cues in a two-way object choice task. An experimenter hid food under one of two bowls and after baiting, indicated the location of the food to the subjects by using one of four different cues. Horses could locate the hidden reward on the basis of the distal dynamic-sustained, proximal momentary and proximal dynamic-sustained pointing gestures but failed to perform above chance level when the experimenter performed a distal momentary pointing gesture. The results revealed that horses could rely spontaneously on those cues that could have a stimulus or local enhancement effect, but the possible comprehension of the distal momentary pointing remained unclear. The results are discussed with reference to the involvement of various factors such as predisposition to read human visual cues, the effect of domestication and extensive social experience and the nature of the gesture used by the experimenter in comparative investigations.
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Farmer, K., Krueger, K., & Byrne, R. (2010). Visual laterality in the domestic horse (Equus caballus) interacting with humans. Anim. Cogn., 13, 229–238.
Abstract: Most horses have a side on which they are easier to handle and a direction they favour when working on a circle, and recent studies have suggested a correlation between emotion and visual laterality when horses observe inanimate objects. As such lateralisation could provide important clues regarding the horse’s cognitive processes, we investigated whether horses also show laterality in association with people. We gave horses the choice of entering a chute to left or right, with and without the passive, non-interactive presence of a person unknown to them. The left eye was preferred for scanning under both conditions, but significantly more so when a person was present. Traditionally, riders handle horses only from the left, so we repeated the experiment with horses specifically trained on both sides. Again, there was a consistent preference for left eye scanning in the presence of a person, whether known to the horses or not. We also examined horses interacting with a person, using both traditionally and bilaterally trained horses. Both groups showed left eye preference for viewing the person, regardless of training and test procedure. For those horses tested under both passive and interactive conditions, the left eye was preferred significantly more during interaction. We suggest that most horses prefer to use their left eye for assessment and evaluation, and that there is an emotional aspect to the choice which may be positive or negative, depending on the circumstances. We believe these results have important practical implications and that emotional laterality should be taken into account in training methods.
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Uller, C., & Lewis, J. (2009). Horses (Equus caballus) select the greater of two quantities in small numerical contrasts. Anim. Cogn., 12(5), 733–738.
Abstract: 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.
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Krueger, K., Flauger, B., Farmer, K., & Maros, K. (2011). Horses (Equus caballus) use human local enhancement cues and adjust to human attention. Anim. Cogn., 14(2), 187–201.
Abstract: This study evaluates the horse (Equus caballus) use of human local enhancement cues and reaction to human attention when making feeding decisions. The superior performance of dogs in observing human states of attention suggests this ability evolved with domestication. However, some species show an improved ability to read human cues through socialization and training. We observed 60 horses approach a bucket with feed in a three-way object-choice task when confronted with (a) an unfamiliar or (b) a familiar person in 4 different situations: (1) squatting behind the bucket, facing the horse (2) standing behind the bucket, facing the horse (3) standing behind the bucket in a back-turned position, gazing away from the horse and (4) standing a few meters from the bucket in a distant, back-turned position, again gazing away from the horse. Additionally, postures 1 and 2 were tested both with the person looking permanently at the horse and with the person alternating their gaze between the horse and the bucket. When the person remained behind the correct bucket, it was chosen significantly above chance. However, when the test person was turned and distant from the buckets, the horses’ performance deteriorated. In the turned person situations, the horses approached a familiar person and walked towards their focus of attention significantly more often than with an unfamiliar person. Additionally, in the squatting and standing person situations, some horses approached the person before approaching the correct bucket. This happened more with a familiar person. We therefore conclude that horses can use humans as a local enhancement cue independently of their body posture or gaze consistency when the persons remain close to the food source and that horses seem to orientate on the attention of familiar more than of unfamiliar persons. We suggest that socialization and training improve the ability of horses to read human cues.
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