Lupine Publishers | Scholarly Journal Of Psychology And Behavioral Sciences
Abstract
The generalisation of
responses to different stimuli depends on the ability to create associations
between stimuli. Stimulus generalisation can be performed for different stimuli
or for different contexts in which the same stimulus is perceived. This study
investigated the stimulus-generalisation abilities of horses in different
contexts. Sixteen horses were involved in this study. During the learning
activity (LA), horses were given the chance to choose between two geometrical
figures (a triangle and a circle) to obtain a food reward; the circle always
corresponded to the correct choice. The rule was considered learned if a horse
was correct more than 70% of the time and made 4 consecutive correct choices.
Then, a generalisation test (GT) with ten devices (5 circles, 5 triangles) was
created to test generalisation. Only eleven horses respected the learning
criteria and were included in the generalisation test. A significant difference
in the number of correct choices between the learning activity and the generalisation
test was observed (Wilcoxon signed-rank test, S=-33; p=0.001; LA: median=6,
min=3, max=9; GT: median=3, min=0, max=5). There was no significant difference
in the number of incorrect choices between the two tests (Student’s t test,
t=-0.91; DF=10; p=0.384). A significant difference in the total number of
choices between the two tests was observed (Student’s t test, t=2.56; DF=10;
p<0.05). This experiment suggested limits in the capacity of horses to
generalise a well-known task in different contexts. Because horses are often
exposed to different environments or contexts, these results provide
interesting and applicable knowledge for equine training and management.
Keywords: Behaviour;
Equine Management; Generalisation; Horse; Learning; Welfare
Introduction
Horses are involved in
many activities that have evolved over time and have changed the human-horse
relationship [1]. Currently, horses perform sports and work activities that
require adaptation to different contexts [2,3]. Horses are continuously
challenged from physical and psychological perspectives and need to understand
information provided by different persons or in different contexts [3,4]. To
succeed in equitation, horses must learn different categories of exercises that
are demanded by riders [5]. However, rider weight and posture, as well as the
intensity applied to cues, are variable, which often results in differences in
the information perceived by the horse [6]. Nevertheless, horses have an
incredible behavioural flexibility that allows them to adapt their responses to
the intensities of the cues given by different riders [7-10]. In addition,
horses are athletes that often participate in competitions. Competition has
been shown to induce physiological modifications in horses related to stress
[5-11]. In competition, riders expect their horses to ignore external stimuli
and to perform as usual in response to trained cues, which requires horses to
generalise those cues from a training environment to a new context with
multiple stimuli, such as the presence of the public [11]. The same situation
might happen each time horses experience a change of ownership or a change in
their living conditions [12]. To summarise, equine living conditions, training
and competitions are full of different stimuli that challenge horses’ coping
strategies [13-15]. In this context, it is important to understand that the
generalisation of a stimulus implies that animals can form associations between
different stimuli (Nicol, 2005). Horses are requested to generalise their
responses to different stimuli over training, either through positive or
negative reinforcement [7]. Stimulus generalisation could be performed from a
group of stimuli with some similarities (e.g.: curved shapes) to a novel
stimulus, which share the same similarities (e.g.: a circle) [16]. However,
stimulus generalisation may also occur as the generalisation of a defined
stimulus to different contexts [17]. Stimulus generalisation to new contexts
appears to be difficult for horses [18-20].
Hence, the
generalisation of a well-known stimulus to different stimuli is a factor in
equine management and welfare [5]. This means that providing more efficient and
reliable training methods for riders and owners can increase the welfare of
horses [6,11]. Therefore, to efficiently improve horse welfare in equine
husbandry and training, riders and owners should learn from scientific
knowledge instead of following common beliefs [15]. The present study aimed to
investigate the ability of equines to generalise a learned task, based on the
same rule, to different contexts. We hypothesised that horses would show the
generalisation of a learned stimulus to a novel test in a different setting.
Methods
Subjects
Sixteen horses (11
geldings; 5 females) older than eighteen months (11.5 ± 6.14 years) were
involved in this study. All horses participated in equestrian activities on a
daily basis. A visual examination was performed by a veterinary doctor to
ensure that none of the animals had vision issues that could impair the tests.
This study was divided into two learning events. All animals were submitted to
a learning activity (LA), which was a reproduction of the test used. The LA
intended to show the discriminative rule to the horses, enabling the selection
of a population of horses that understood the rule before performing the second
test. The discriminative rule was considered learned if a horse was correct
more than 70% of the time and made 4 consecutive correct choices. Only horses
that respected these criteria were included in the second test, which was a
generalisation test (GT).
Material
“Philbox”, the
dispositive adapted and he was used for the LA in this experiment (Figure 1).
The device consisted of two white panels; removable black shapes (a circle or a
triangle) could be placed in front of the panels, and a hidden operator could
insert treats on a food tray through a hole under each shape. A second operator
led the horses to the panels. Ten “Pesadelo” devices were created to test the
equine generalisation abilities (Figure 2). Each of these devices included a
tilting mechanism, with one black shape painted on a white panel on the top (5
had a circle, and 5 had a triangle) and an inverted container on the bottom.
Treats were placed in the containers, which each had a cover. For all devices
marked by a circle, this cover was pierced such that the treats fell on the
ground when the animals pushed or pulled the panel. For devices marked by a
triangle, the cover was intact, so the treats did not fall when the animal
pushed or pulled the panel. Some holes were created on the container to ensure
that both devices had the same odour, regardless of cover type. There was a
tray under each container. No operators were needed to run this device.
Figure 1: Philbox. The Philbox is a modified device for performing cognitive
tests. The Philbox includes two removable geometrical shapes (circle and
triangle) and a hidden operator who provides treats when the animals touch the
panel with the correct shape.
Figure 2: Pesadelo. A Pesadelo is a device created to perform cognitive
tests. The device includes a tilting mechanism with a shape-marked panel on one
side and a treat in a container on the other side. To obtain the treat, a horse
must push the panel (circle or triangle), such that the shape-marked panel
tilts down and forward, the container tilts up and backward, and the treat
drops onto the floor.
Procedure
A habituation session to
the Philbox device was performed, as described. The setting was presented to
the subjects, and spontaneous approaches and interactions with the device were
rewarded with a treat. The session consisted of twelve efforts with the shapes
removed from the devices. The initial phase of the session included 6 attempts
(3 on the right and 3 on the left) using a treat on the panels as a lure; an
additional reward was given each time the horses touched the panels. The horses
then made 6 more attempts, for which they received a reward only upon touching
the panels. A habituation session for the Pesadelo device was also performed to
show horses the mechanism of pushing/pulling the panel to obtain treats. For
this session, two devices with the shape panel replaced by a whole white panel
were used. Horses were given 3 minutes of free contact with the two devices, in
which any spontaneous contact with the panel was reinforced with a treat that
felt from the container. For this purpose, each time a horse obtained a treat,
an operator led the horse to the other device, while a second operator refilled
the empty container with treats.
The LA were performed
using the Philbox device and lasted five minutes for each horse. Horses had the
possibility to choose between the shapes and received a reward (food treat)
upon touching the correct shape (always the circle) with their noses (positive
reinforcement). The development of a side preference was avoided by following
predefined sequences of four figures, with a randomised order of appearance,
thus avoiding any recognisable pattern. In addition, a food treat was hidden
behind each shape to provide the same olfactory cue for both the circle and
triangle. There was no limit to the number of attempts horses could perform
during the 5 minutes of the test. Once a choice was made, horses were walked
around by the operator and returned to the starting position. Thus, the horses
that made choices faster could perform more attempts during the 5 minutes of
the test. Each horse was led to a distance of 1.5 metres in front of the panels
and then freed to interact with the setting. The operator stopped at 1.5
metres, stayed in a neutral position, and did not interact with the animal
until a choice was made. Horses that made 70% or more correct choices, with at
least 4 consecutive correct choices, were subsequently included in the GT.
There was a time lapse of 48 hours between the two tests for all horses. The GT
lasted 5 minutes for each horse. The setting consisted of ten Pesadelo devices
(5 circles and 5 triangles) placed in a controlled testing area inside of a
riding arena (Figure 3). Each device provided only one treat. The devices were
randomly positioned in the setting area to permit the horse to easily access
the two options (triangle and circle). Each horse was completely free in the
testing area, and the operator left the riding arena and the visual field of
the horse. The performance parameters for both tests included correct and
incorrect choices and the total number of choices. For the GT, a choice was
considered correct both the first and second time a horse pushed/pulled the
same panel with a circle, even if the treat reward was only achieved during the
first interaction. The same rule was applied for incorrect choices. If the
horse returned to the same device a third time, that choice was not considered,
neither correct or incorrect. Each horse was considered its own control.
Figure 3: Generalisation test setting. Ten Pesadelo devices were positioned
in a controlled area to test equine generalisation capacities.
Statistical Analysis
Statistical analysis was
carried out using 9.4 SAS software (2002-2012 by SAS Institute Inc., Cary, NC,
USA). The significance threshold was classically fixed at 5%. Comparisons among
the horses’ performances during the LA and the GT involved paired samples. To
use the paired Student’s t test, normality was tested on the difference of the
results in the LA and in the GT for the following parameters: “correct
choices”, “incorrect choices” and “total number of choices”. For the “correct
choices”, assumption of normality was not verified, so the non-parametric
signed-rank Wilcoxon test was preferred. Normality was verified for “incorrect
choices” and “total number of choices”; hence, the parametric Student t test
was used.
Results
From the 16 initial horses,
five did not learn the discriminative rule, so they were not included in the
GT. The final population of horses comprised 11 subjects (7 geldings; 4
females). Only these horses were considered for the statistical analysis.
Figure 4 compares these horses’ performances between the two tests. A
significant difference in the number of correct choices between the learning
activity and the generalisation test was observed (Wilcoxon Signed-Rank test,
S=-33; p=0.001; LA: median=6, min=3, max=9; GT: median=3, min=0, max=5). Horses
made two times fewer correct choices in the GT than in the LA. There was no
significant difference in the number of incorrect choices between the two tests
(Student’s t test, t=-0.91; DF=10; p=0.384).
Figure 4: Comparison of horses’ performances in the two tests (mean ± SD of
choices). The learning activity is represented by light grey, and the
generalisation test is represented by dark grey. ***: highly significant
p-value, p=0.001; *: significant p-value, p<0.05.
A significant difference
was observed in the total number of choices between the two tests, (Student’s t
test, t=2.56; DF=10; p<0.05). Horses made a greater number of choices in the
LA than in the GT.
Discussion and Conclusion
This experiment showed that
horses who learned a specific discrimination task had a lower performance when
the task was presented for the first time in a different context and setting.
This result was emphasised by the decrease in the total number of choices and
the number of correct choices between the learning and the GTs. The absence of
a significant difference in the incorrect choices between the tests was
probably related to the reduced total number of choices in the GT when compared
to the LA. Horses made fewer attempts in the GT and often chose the wrong shape
or device. The decrease in the horses’ performance between tests suggests that
the generalisation of a learned task between contexts might require training
and repetition. Even if the discriminative rule had been the same in both
tests, the setting was completely different. The GT involved a
three-dimensional setting with multiple devices, with only one positive
reinforcement per device. For the LA, horses had panels simultaneously
presenting all possible choices in their visual field, while for the GT, it was
essential for horses to walk between the devices to reach all of them. The new
context of the test can have impacted the performance in the GT. In addition,
for the LA, an operator was always present. His presence could have represented
a help for the animal. However, in our study, the operators were trained to
stay in a neutral position and avoid any interaction with the horses to prevent
them from influencing the horses’ choices. One could argue that the time (i.e.
48h) between tests could have a role in memorisation and, consequently, the
generalisation of the rule. Nevertheless, memory in horses seems to be reliable
and longlasting through life, as described by Hanggi and Ingersoll (2009).
Our results differ from
those of Christensen et al. (2008), who conducted a study in which horses were
submitted to a GT between stationary objects of the same colour with varying
shapes in the same setting conditions. That study changed the rewarded shape
between tests, while in the present study, the rewarded shape (the circle)
remained the same between tests, but the setting was changed. Therefore, the
generalisation of a well-known stimulus might depend on the context and
environment [20]. This hypothesis is supported by the results, who created a
setting with a lever near two buckets in an area open to horses. Horses learned
that once they pressed the lever, they could have a food reward. Then, in a
Y-maze test, a lever pointed to the direction of the correct side of the maze,
where horses could find a food reward. They found that horses’ performance
decreased from the bucket test to the Y-maze test. Even if the rule, i.e. the
presence of a lever, was the same to obtain a food reward in both tests, the
manner to follow the rule was different. Indeed, horses are accustomed to
exploring new objects by touching or licking them; therefore, the exploratory
behaviour of horses may have spontaneously provided the manners to use the
lever to get a reward. However, in the Y-maze, this natural behaviour does not
lead to any reward, so horses probably needed to find new coping strategies,
which requires time and experience. Conversely, in our study, horses could
obtain the reward by following the same rule with the same manner in the two tests,
i.e. by pressing on a circle, which provided the same reliable information that
horses could use for both tests. We observed a decrease in horses’ performances
between the two tests, indicating that context features other than the manner
to follow the rule can influence the generalisation abilities of horses.
Research findings are of
great importance and should be considered in equine welfare and management
because these findings often contradict commonly held beliefs about equine
cognition and learning abilities [10-16]. Horses are part of a worldwide market
and are moved across countries, which often implies regrouping with other
conspecifics [18].
The ease of habituation
to new living conditions is a serious welfare concern in horses that often results
in misunderstandings in the human-horse relationship [4,6]. For example, if a
horse is moved to novel husbandry conditions, its behavioural response to a
well-known stimulus and the resulting coping strategies could be different from
the original response and strategies, and these differences could be justified
by the context modification, regardless of the horse’s previous habituation to
that stimulus. The same problem could occur during competition because horses
must perform previously learned exercises in new contexts [5]. In conclusion,
this experiment suggested some limits in the capacity of horses to generalise a
well-known task to different contexts. This study demonstrated that horses’
perception of different stimuli is context specific. Increasing our knowledge
about the generalisation abilities of these animals is of great importance to
improve equine management and training. Further research is still needed to
fully understand horses’ generalisation abilities, especially focusing on the
ability to generalise similar information in the same context, and to measure
the influence of this ability on equine management and training.
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