Abstract: With very few exceptions, no coherent model of representing the self exists for nonhuman species. According to our hypothesis, understanding of the Self as an object’ can also be found in a wide range of animals including the dog, a fast-moving terrestrial predator/scavenger, with highly developed senses and complex cognitive capacity. We tested companion dogs in three experiments in which they faced three different variations of the same physical challenge: passing through an opening in a wall. We predicted that if dogs are capable of representing their own body size, they will react differently when faced with adequate or too small openings. We found that dogs started to move towards and approached the too small openings with significantly longer latencies than the suitable ones; and upon reaching it, they did not try to get through the too small openings. In another experiment, the medium-size (still large enough) opening was approached with latencies that fell between the latencies measured in the cases of the very large or the too small openings. Having discussed the potential underlying mechanisms, we concluded that our results convincingly assume that dogs can represent their own body size in novel contexts.
Discussion
In
a series of experiments where dogs had to pass through a single opening
presented on a wall, we found that the size of the opening affected
dogs’ behavior both before and during their approach to the opening, and
also whether they attempted to get through it. In Experiment 1,
similarly to the cognitive bias paradigm (Pogány et al. 2018),
dogs were repeatedly exposed to either a too small or a large opening,
then at the end they faced a mid-size opening (still large enough to
pass through). We found that dogs approached the too small opening
significantly later than the large one, and the latency to approach the
mid-size opening fell in between. In Experiment 2 the opening was
gradually downsized from a comfortably large to a too small opening at
which point the dogs did not go through. We found that dogs started to
move towards and reached the large enough openings sooner than the one
that eventually was proven to be too small. In the final trial, where
the opening was enlarged to the last big enough size, significantly more
dogs attempted to pass through than in the previous (too small opening)
trial. Finally, in Experiment 3 we found that such anatomical features
that mostly affect the body proportions, but not the weight of a dog
(i.e. achondroplasia), had no effect on how dogs assess the suitability
of an opening to pass through. Namely, when we provided dogs with the
same size (large enough) rectangular opening in a vertical or horizontal
arrangement, we did not find that short-legged dogs approached the
horizontal (hence for them still comfortable) opening sooner than the
long-legged dogs did.
At this point we know of only one publication where body size awareness (or any sort of body awareness) was tested in dogs (Maeda and Fujita 2010). In that paper the door choice paradigm was used (simultaneously offering two, differently sized doors, both were large enough for the dogs) and authors found a clear preference for the larger door. Those results, therefore, did not indicate body size awareness in dogs, but a possible preference for the more convenient (larger) opening. In the case of human infants, the development of body awareness as a cognitive capacity is usually tested through such erroneous decisions that indicate that children in a given age cohort have more or less difficulty with the representation of their own body as an ‘obstacle’, or they have no clear representation of their own body size (Moore et al. 2007). Brownell et al. (2007), for example, showed that toddlers between 18 and 26 months show a decreasing frequency of the aforementioned errors when trying to pass through an impossibly narrow opening on a wall; meanwhile, they could use a short (0.3 by 0.3 m) opening at this time. In that article, based on the results from four other tasks with the same children, the authors concluded that body awareness develops step by step during the first years of life. We must note, however, that when conclusions are drawn on the basis of only one behavioral parameter (frequency of errors), the resolution of a study is rather low regarding the difficulties of ruling out the alternative explanations. For example, in case of the study of Brownell et al. (2007), it is not known whether the infants made a choice before or during their approach to the openings, or they simply used a trial-and-error strategy. In our experiments with dogs we used multiple parameters that may provide finer details of decision making. By measuring the latency of starting to move towards, and the latency of arriving to the opening, we tackled the possible differences in the a priori decision making of our subjects. Our results are in line with the results of the cognitive bias paradigm where subjects approach the reinforcing stimulus faster than the not reinforcing one and later when they are facing with the ambiguous stimulus they hesitate and the mean latency of approaching falls in between (Mendl et al. 2009, 2010; Pogány et al. 2018). Consequently, when dogs approached a (too small) opening with longer latency, we can conclude that they found it less likely suitable to pass through, and because of the experimental setup, this decision was most probably made by relating the apparent opening size to the mental representation of their own body size. We should remember that ‘too small’ openings except in the habituation phase of Experiment 1 in these experiments were still reasonably ‘big’, calculated by formulas based on the actual size of each individual subject. Additionally, by comparing the attempts to get through the opening in Experiment 2, this showed that when dogs were facing a slightly larger opening after their trial with the too small opening, they did not hesitate to pass through the large enough door. This fact again underlines that dogs decide about the suitability of the individual opening sizes on a case by case basis, likely by using their own body size representation as a template. We must also add at this point that when we mention a ‘template’ of the body size, it is obviously such a mental construct that develops in dogs through a priori encounters with various obstacles beginning from their early ontogeny. However, just because the creation of this template requires experience, it does not mean that the dog has to re-learn each obstacle (i.e. opening size) again and again; on the contrary, the template about its own size makes these types of decisions fast and easy. It is also worthy to mention that the possible connection between experience and the formation of body awareness (i.e. the mental ‘template’) is still unclear even in the case of human infants (see, e.g. Filippetti et al. 2014; Samuels 1986).
In this study our goal was to find evidence in dogs for one of the fundamental building blocks of so-called objective self, body awareness (Moore et al. 2007), while preferably excluding simpler mechanisms for solving the experimental tasks. By providing only one opening at a time, we excluded the option of simply choosing the larger (more convenient, or safer) door (dogs: Maeda and Fujita 2010; children: Brownell et al. 2007), and we did not base our analysis on the number of attempts or the latency of passing through, as we argue that these are mostly dependent on the motivation level of the individual subjects. Similarly, in Experiment 2, we gradually downsized the opening till the subject itself decided that the particular opening size is too small to go through thus we could eliminate the possible differences in the motivation level of the subjects. One could argue that dogs may approach the too small opening with longer latencies because they lost interest in the task towards the end of the experiment; however, we did not find this type of slowing down in the case of the repeated trials with the large enough openings in Experiment 1.
Of course, it is possible that the subjects could try to force themselves through each opening size, and only where they cannot prevail would they give up the attempt. However, we found that this was not the case in Experiment 2, where significantly less dogs even tried to get through the too small opening; meanwhile most of them attempted (and succeeded in) getting through a somewhat larger one. As Franchak and Adolph (2012) underlined, in case of the original door choice tasks, the so-called ‘error’ (i.e. trying to get through the too small opening) has no real, high cost to the individual; consequently, they are not really motivated to avoid it. In children, they found that when the cost was not just getting entrapped in the too narrow opening, but also possibly falling down behind it, the subjects did not try passing through the too small openings. Although in nature entrapment could result in the death of the animal while it tries to squeeze itself through a too narrow opening, there is also the possibility of turning back without serious injury. The results of Franchak and Adolph (2012) supported ours, as dogs did not even attempt to go through if the opening appeared to be too small for them, although the cost would be very low. Furthermore, the latencies of leaving the start point and arriving at the opening showed that dogs distinguished between suitable and unsuitable opening sizes well ahead of actually trying them.
Another possible mechanism that could help the dogs to find out which opening was large enough or too small for them would be the a priori experience with the doors. On the one hand, we could argue that none of our experimental devices were familiar to the dogs; therefore they could not have any knowledge about the suitability of the individual openings. On the other hand, in Experiment 2, where we used all but one opening size only once—except in the last trial dogs did not even have the opportunity to use their freshly gained experience for any of the particular opening sizes coming from the previous trial. Still, it is possible that they would develop some sort of memory-based preference for the ‘conveniently’ sized openings along the serial exposures to the smaller and smaller openings of the actual test; however, this is unlikely because it would result in a steadily increasing latency of approaching. Instead, what we found was a sharp decline of willingness to approach and use the ‘too small’ door in Experiment 2.
Also, one could argue that instead of comparing the size of an actually seen opening to its own body size, dogs with a mechanism different from body-size awareness could somehow estimate the absolute size of an opening and based on that, they could make a decision before they reached the opening in question. The results of Experiment 3 contradict this explanation. Here, dogs faced four times the same size opening, where only the alignment of the opening changed from vertical to horizontal in the last trial. If dogs would mostly rely on a representation of a particular opening size, they would recognize that the two variants are equally large, and they would approach the horizontal opening with the same speed as the vertical ones. However, we found that dogs arrived to the horizontal opening later than to the vertical ones. Another alternative mechanism could be that instead of the size of the opening’s surface, dogs base their decision on the height and width of the opening, and when we ‘rotated’ the vertical opening to the horizontal alignment, the height of the new opening fell into the less suitable category resulting in a slower approach from the subjects.
Another possible explanation is that dogs might simply learn about particular opening sizes during their everyday interactions with their physical environment; thus in our experiments they could rely on their positive or negative experiences from the past and when they go through a new opening they compare its size with the previously learned sizes. Although learning from the experiences of interactions with the physical environment is plausible during the development of the own body size template, based on our results we argue that in our case not only external cues, i.e. learning about the particular openings during the tests shaped the decision making of the dogs. In Experiment 3, we found that short-legged dogs arrived to the horizontal opening later than the long-legged dogs. If dogs’ responses would mostly depend on previous experiences regarding suitable openings, we would expect just the opposite: short-legged dogs would remain similarly fast regardless of the alignment of the opening (as the horizontal opening was still comfortably high for them); meanwhile long-legged dogs would slow down due to the ungainly alignment of the horizontal opening. As our results showed the opposite, the theory of previous experience-driven decision making is less likely; instead, the later arrival to the opening in both groups can be rather explained with the effect of surprise (i.e. the alignment of the opening had been changed), and also with the possibly slower locomotion of the short legged dogs. Similarly, in Experiment 2 during the last trial when the door size was enlarged again one could expect that dogs should have been as fast as when they were facing that particular size for the first time. In other words, if dogs would rely only on their past experiences regarding the opening sizes, they would pass through the large enough door sooner in the last trial than in the too small one just before. However, we found that there was no difference between the latencies in the case of the last two trials probably because of the negative experience of facing a too small opening in the previous trial. This hesitation may also support the existence of a priori decision making of the dogs before they actually approach an opening.
At this point we know of only one publication where body size awareness (or any sort of body awareness) was tested in dogs (Maeda and Fujita 2010). In that paper the door choice paradigm was used (simultaneously offering two, differently sized doors, both were large enough for the dogs) and authors found a clear preference for the larger door. Those results, therefore, did not indicate body size awareness in dogs, but a possible preference for the more convenient (larger) opening. In the case of human infants, the development of body awareness as a cognitive capacity is usually tested through such erroneous decisions that indicate that children in a given age cohort have more or less difficulty with the representation of their own body as an ‘obstacle’, or they have no clear representation of their own body size (Moore et al. 2007). Brownell et al. (2007), for example, showed that toddlers between 18 and 26 months show a decreasing frequency of the aforementioned errors when trying to pass through an impossibly narrow opening on a wall; meanwhile, they could use a short (0.3 by 0.3 m) opening at this time. In that article, based on the results from four other tasks with the same children, the authors concluded that body awareness develops step by step during the first years of life. We must note, however, that when conclusions are drawn on the basis of only one behavioral parameter (frequency of errors), the resolution of a study is rather low regarding the difficulties of ruling out the alternative explanations. For example, in case of the study of Brownell et al. (2007), it is not known whether the infants made a choice before or during their approach to the openings, or they simply used a trial-and-error strategy. In our experiments with dogs we used multiple parameters that may provide finer details of decision making. By measuring the latency of starting to move towards, and the latency of arriving to the opening, we tackled the possible differences in the a priori decision making of our subjects. Our results are in line with the results of the cognitive bias paradigm where subjects approach the reinforcing stimulus faster than the not reinforcing one and later when they are facing with the ambiguous stimulus they hesitate and the mean latency of approaching falls in between (Mendl et al. 2009, 2010; Pogány et al. 2018). Consequently, when dogs approached a (too small) opening with longer latency, we can conclude that they found it less likely suitable to pass through, and because of the experimental setup, this decision was most probably made by relating the apparent opening size to the mental representation of their own body size. We should remember that ‘too small’ openings except in the habituation phase of Experiment 1 in these experiments were still reasonably ‘big’, calculated by formulas based on the actual size of each individual subject. Additionally, by comparing the attempts to get through the opening in Experiment 2, this showed that when dogs were facing a slightly larger opening after their trial with the too small opening, they did not hesitate to pass through the large enough door. This fact again underlines that dogs decide about the suitability of the individual opening sizes on a case by case basis, likely by using their own body size representation as a template. We must also add at this point that when we mention a ‘template’ of the body size, it is obviously such a mental construct that develops in dogs through a priori encounters with various obstacles beginning from their early ontogeny. However, just because the creation of this template requires experience, it does not mean that the dog has to re-learn each obstacle (i.e. opening size) again and again; on the contrary, the template about its own size makes these types of decisions fast and easy. It is also worthy to mention that the possible connection between experience and the formation of body awareness (i.e. the mental ‘template’) is still unclear even in the case of human infants (see, e.g. Filippetti et al. 2014; Samuels 1986).
In this study our goal was to find evidence in dogs for one of the fundamental building blocks of so-called objective self, body awareness (Moore et al. 2007), while preferably excluding simpler mechanisms for solving the experimental tasks. By providing only one opening at a time, we excluded the option of simply choosing the larger (more convenient, or safer) door (dogs: Maeda and Fujita 2010; children: Brownell et al. 2007), and we did not base our analysis on the number of attempts or the latency of passing through, as we argue that these are mostly dependent on the motivation level of the individual subjects. Similarly, in Experiment 2, we gradually downsized the opening till the subject itself decided that the particular opening size is too small to go through thus we could eliminate the possible differences in the motivation level of the subjects. One could argue that dogs may approach the too small opening with longer latencies because they lost interest in the task towards the end of the experiment; however, we did not find this type of slowing down in the case of the repeated trials with the large enough openings in Experiment 1.
Of course, it is possible that the subjects could try to force themselves through each opening size, and only where they cannot prevail would they give up the attempt. However, we found that this was not the case in Experiment 2, where significantly less dogs even tried to get through the too small opening; meanwhile most of them attempted (and succeeded in) getting through a somewhat larger one. As Franchak and Adolph (2012) underlined, in case of the original door choice tasks, the so-called ‘error’ (i.e. trying to get through the too small opening) has no real, high cost to the individual; consequently, they are not really motivated to avoid it. In children, they found that when the cost was not just getting entrapped in the too narrow opening, but also possibly falling down behind it, the subjects did not try passing through the too small openings. Although in nature entrapment could result in the death of the animal while it tries to squeeze itself through a too narrow opening, there is also the possibility of turning back without serious injury. The results of Franchak and Adolph (2012) supported ours, as dogs did not even attempt to go through if the opening appeared to be too small for them, although the cost would be very low. Furthermore, the latencies of leaving the start point and arriving at the opening showed that dogs distinguished between suitable and unsuitable opening sizes well ahead of actually trying them.
Another possible mechanism that could help the dogs to find out which opening was large enough or too small for them would be the a priori experience with the doors. On the one hand, we could argue that none of our experimental devices were familiar to the dogs; therefore they could not have any knowledge about the suitability of the individual openings. On the other hand, in Experiment 2, where we used all but one opening size only once—except in the last trial dogs did not even have the opportunity to use their freshly gained experience for any of the particular opening sizes coming from the previous trial. Still, it is possible that they would develop some sort of memory-based preference for the ‘conveniently’ sized openings along the serial exposures to the smaller and smaller openings of the actual test; however, this is unlikely because it would result in a steadily increasing latency of approaching. Instead, what we found was a sharp decline of willingness to approach and use the ‘too small’ door in Experiment 2.
Also, one could argue that instead of comparing the size of an actually seen opening to its own body size, dogs with a mechanism different from body-size awareness could somehow estimate the absolute size of an opening and based on that, they could make a decision before they reached the opening in question. The results of Experiment 3 contradict this explanation. Here, dogs faced four times the same size opening, where only the alignment of the opening changed from vertical to horizontal in the last trial. If dogs would mostly rely on a representation of a particular opening size, they would recognize that the two variants are equally large, and they would approach the horizontal opening with the same speed as the vertical ones. However, we found that dogs arrived to the horizontal opening later than to the vertical ones. Another alternative mechanism could be that instead of the size of the opening’s surface, dogs base their decision on the height and width of the opening, and when we ‘rotated’ the vertical opening to the horizontal alignment, the height of the new opening fell into the less suitable category resulting in a slower approach from the subjects.
Another possible explanation is that dogs might simply learn about particular opening sizes during their everyday interactions with their physical environment; thus in our experiments they could rely on their positive or negative experiences from the past and when they go through a new opening they compare its size with the previously learned sizes. Although learning from the experiences of interactions with the physical environment is plausible during the development of the own body size template, based on our results we argue that in our case not only external cues, i.e. learning about the particular openings during the tests shaped the decision making of the dogs. In Experiment 3, we found that short-legged dogs arrived to the horizontal opening later than the long-legged dogs. If dogs’ responses would mostly depend on previous experiences regarding suitable openings, we would expect just the opposite: short-legged dogs would remain similarly fast regardless of the alignment of the opening (as the horizontal opening was still comfortably high for them); meanwhile long-legged dogs would slow down due to the ungainly alignment of the horizontal opening. As our results showed the opposite, the theory of previous experience-driven decision making is less likely; instead, the later arrival to the opening in both groups can be rather explained with the effect of surprise (i.e. the alignment of the opening had been changed), and also with the possibly slower locomotion of the short legged dogs. Similarly, in Experiment 2 during the last trial when the door size was enlarged again one could expect that dogs should have been as fast as when they were facing that particular size for the first time. In other words, if dogs would rely only on their past experiences regarding the opening sizes, they would pass through the large enough door sooner in the last trial than in the too small one just before. However, we found that there was no difference between the latencies in the case of the last two trials probably because of the negative experience of facing a too small opening in the previous trial. This hesitation may also support the existence of a priori decision making of the dogs before they actually approach an opening.
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