ArticleLiterature Review

Vision in dogs

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Abstract

Compared with the visual system in human beings, the canine visual system could be considered inferior in such aspects as degree of binocular overlap, color perception, accommodative range, and visual acuity. However, in other aspects of vision, such as ability to function in dim light, rapidity with which the retina can respond to another image (flicker fusion), field of view, ability to differentiate shades of gray, and perhaps, ability to detect motion, the canine visual system probably surpasses the human visual system. This has made the dog a more efficient predator in certain environmental situations and permits it to exploit an ecological niche inaccessible to humans.

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... The eye laterality of a species is closely related to their lifestyle, and further how they use their eyes (Land, 2015). As shown in recently constructed ancient dog model (Historic Environment Scotland, 2019), the eyes of typical dogs are directed 20 ° laterally (Miller & Murphy, 1995). With such laterality, dogs have wide field of view (240 °), which would make panoramic scanning of the horizons effortless with only a few slow and large saccades and long fixations. ...
... With such laterality, dogs have wide field of view (240 °), which would make panoramic scanning of the horizons effortless with only a few slow and large saccades and long fixations. At the same time, their skull shape makes them to have binocular view of 30-60 ° (Sherman & Wilson, 1975), much narrower than that of humans (140 °), and also blocked by their nose below certain height (Miller & Murphy, 1995). Further, it has been suggested that the right and left peripheral portion of their binocular view (15 ° each) would be further limited due to a lack of alpha ganglion cells in the corresponding areas of the retina (Peichlcu, 1992). ...
... However, during activities such as hunting they do appear to have sufficient ability to judge distances to far away objects. They probably do so using monocular clues (Miller & Murphy, 1995;Walk & Gibson, 1961). ...
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Eye movement of a species reflects the visual behavior strategy that it has adapted to during its evolution. What are eye movements of domestic dogs (Canis lupus familiaris) like? Investigations of dog eye movements per se have not been done, despite the increasing number of visuo-cognitive studies in dogs using eye-tracking systems. To fill this gap, we have recorded dog eye movements using a video-based eye-tracking system, and compared the dog data to that of humans. We found dog saccades follow the systematic relationships between saccade metrics previously shown in humans and other animal species. Yet, the details of the relationships, and the quantities of each metric of dog saccades and fixations differed from those of humans. Overall, dog saccades were slower and fixations were longer than those of humans. We hope our findings contribute to existing comparative analyses of eye movement across animal species, and also to improvement of algorithms used for classifying eye movement data of dogs.
... Stimuli were presented on two identical monitors (VG248QE, ASUSTeK Computer Inc., Taipei, Taiwan). Their refresh rate was set at 100 Hz, to prevent possible biases on motion detection, due to dogs' higher flicker fusion frequency (Miller and Murphy 1995). Monitors were connected to a PC (Optiplex 960, Dell Inc., Round Rock, Texas, USA). ...
... Regardless of which of the two parameters is considered, the results indicate that dogs' local integration mechanisms are at least as efficient as they are in humans and are therefore unlikely to play a major role in determining dogs' higher threshold of coherent motion detection. In addition, the efficiency in local integration mechanisms is in line with dogs' alleged skillfulness at detecting locally moving stimuli, such as a prey moving in the distance (Miller and Murphy 1995). ...
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Knowledge about the mechanisms underlying canine vision is far from being exhaustive, especially that concerning post-retinal elaboration. One aspect that has received little attention is motion perception, and in spite of the common belief that dogs are extremely apt at detecting moving stimuli, there is no scientific support for such an assumption. In fact, we recently showed that dogs have higher thresholds than humans for coherent motion detection (Kanizsar et al. in Sci Rep UK 7:11259, 2017). This term refers to the ability of the visual system to perceive several units moving in the same direction, as one coherently moving global unit. Coherent motion perception is commonly investigated using random dot displays, containing variable proportions of coherently moving dots. Here, we investigated the relative contribution of local and global integration mechanisms for coherent motion perception, and changes in detection thresholds as a result of repeated exposure to the experimental stimuli. Dogs who had been involved in the previous study were given a conditioned discrimination task, in which we systematically manipulated dot density and duration and, eventually, re-assessed our subjects' threshold after extensive exposure to the stimuli. Decreasing dot duration impacted on dogs' accuracy in detecting coherent motion only at very low duration values, revealing the efficacy of local integration mechanisms. Density impacted on dogs' accuracy in a linear fashion, indicating less efficient global integration. There was limited evidence of improvement in the re-assessment but, with an average threshold at re-assessment of 29%, dogs' ability to detect coherent motion remains much poorer than that of humans.
... These predators all have dichromatic visual systems; i.e., they have only two types of cone visual receptors with distinct spectral sensitivities, not the four characteristic of most birds or the three found in most humans [13]. Because dichromatic mammals lack red-green color discrimination, they are unlikely to detect many of the chromatic visual cues evident to birds and humans [13][14][15]. Studies of visual ecology have considered how prey appear to various types of predators (birds, insects and fish) for many types of prey, including insects and birds [16,17], fish [18], cuttlefish [19], crustaceans [20], primates [21] and lizards [11]. ...
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Colorful feathers have long been assumed to be conspicuous to predators, and hence likely to incur costs due to enhanced predation risk. However, many mammals that prey on birds have dichromatic visual systems with only two types of color-sensitive visual receptors, rather than the three and four photoreceptors characteristic of humans and most birds, respectively. Here, we use a combination of multispectral imaging, reflectance spectroscopy, color vision modelling and visual texture analysis to compare the visual signals available to conspecifics and to mammalian predators from multicolored feathers from the Indian peacock (Pavo cristatus), as well as red and yellow parrot feathers. We also model the effects of distance-dependent blurring due to visual acuity. When viewed by birds against green vegetation, most of the feathers studied are estimated to have color and brightness contrasts similar to values previously found for ripe fruit. On the other hand, for dichromat mammalian predators, visual contrasts for these feathers were only weakly detectable and often below detection thresholds for typical viewing distances. We also show that for dichromat mammal vision models, the peacock’s train has below-detection threshold color and brightness contrasts and visual textures that match various foliage backgrounds. These findings are consistent with many feathers of similar hue to those studied here being inconspicuous, and in some cases potentially cryptic, in the eyes of common mammalian predators of adult birds. Given that birds perform many conspicuous motions and behaviors, this study suggests that mammalian predators are more likely to use other sensory modalities (e.g., motion detection, hearing, and olfaction), rather than color vision, to detect avian prey. This suggests new directions for future behavioral studies and emphasizes the importance of understanding the influence of the sensory ecology of predators in the evolution of animal coloration.
... After cataract surgery, significant negative changes occur regarding the refractive ability of the eye and visual quality deteriorates. In other words, aphakic eyes cannot clearly see objects that are near or far (Miller & Murphy, 1995). Lens make up for 40D (66%) of the refractive ability of a healthy dog's eye which is 60D. ...
... For the following reasons, we consider that the domestic cat (Felis silvestris catus) is a good candidate species for the comparative study of susceptibility to geometrical illusions. Like the other species mentioned above, cats depend in large part on visual cues that are likely similar to those used by other mammalian species, including humans, to navigate in their environment (see for some comparison, Blake, 1979;Miller & Murphy, 1995). Like dogs, they belong to the order Carnivora, but in contrast, they have a semiarboreal lifestyle. ...
Article
The comparative study of the perception of visual illusions between different species is increasingly recognized as a useful noninvasive tool to better understand visual perception and its underlying mechanisms and evolution. The aim of the present study was to test whether the domestic cat is susceptible to the Delboeuf illusion in a manner similar to other mammalian species studied to date. For comparative reasons, we followed the methods used to test other mammals in which the animals were tested in a 2-way choice task between same-size food stimuli presented on different-size plates. In 2 different control conditions, overall the 18 cats tested spontaneously chose more often the larger amount of food, although at the individual level, they showed interindividual differences. In the Delboeuf illusion condition, where 2 equal amounts of food were presented on different-size plates, all cats chose the food presented on the smaller plate more often than on the larger one, suggesting that they were susceptible to the illusion at the group level, although at the individual level none of them performed significantly above chance. As we found no correlation between the cats’ overall performance in the control conditions and their performance in the illusion condition, we propose that the mechanisms underlying spontaneous size discrimination and illusion perception might be different. In the discussion, we compare the results of the present study with the results for other previously tested mammals and highlight some possible reasons for their similarities and differences.
... Recent studies in human beings revealed that the posterior corneal curvature effectively reduces total corneal astigmatism, partially compensating for anterior corneal astigmatism. 37 In dogs, it is quite possible that the posterior corneal curvature, together with other morphological and structural variations reported in the face and the retina, [38][39][40] may also vary between breeds, minimising the impact of interbreed variations noted in the anterior corneal curvature on vision. However, none of the previous studies has particularly evaluated French bulldogs to prove that this breed is not an exception. ...
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Background Keratometry is clinically important and is routinely performed as part of human ophthalmic examination. In veterinary ophthalmology, little is known about keratometry in dogs, and its practical application has been limited. The present study aimed to describe keratometry in some dog breeds popular in Japan using a handheld keratometer. Methods Client-owned dogs of various signalment were enrolled prospectively in the keratometry examination. Interbreed variations in mean corneal curvatures (R1R2avg) and corneal astigmatism (Δ(R1−R2)) were evaluated statistically with respect to their bodyweight based on the data which fulfilled the predetermined inclusion criteria. P<0.05 was considered statistically significant. Results On examination of 237 dogs from 16 different breeds, R1R2avg (mean±sd) ranged from 7.54±0.30 mm in Pomeranians to 9.28±0.19 mm in golden retrievers. Δ(R1−R2) (mean±sd) ranged from 0.22±0.11 mm in miniature schnauzers to 0.57±0.30 mm in French bulldogs. Conclusion The present study successfully described keratometry in 16 dog breeds. The study revealed considerable interbreed variations in both R1R2avg and Δ(R1−R2), which did not necessarily correlate with bodyweight. These results are useful both clinically in fitting contact lenses in the management of corneal diseases and non-clinically in optometric studies in dogs.
Chapter
The lens contributes two‐thirds of the refractive power of the eye. As such, it plays an important role in vision. Although less so in companion animals than in humans, the lens also contributes to accommodation, so that both near and far objects come into focus. For the lens to function as a refractive surface, it must maintain transparency. Transparency may be impacted by age‐related denseness of the lens nucleus. This so‐called nuclear sclerosis creates haziness within the lens. Although this haziness does not typically impact vision, it is easily observed by the astute observer. Nuclear sclerosis may be confused for a cataract. A cataract is an opacity within the lens or lens capsule. This opacity may or may not progress over time. When cataracts progress, they typically move through a series of stages of development, from incipient to immature, and mature to hypermature. Immature cataracts are best addressed via phacoemulsification and artificial lens implantation. As cataracts progress, perioperative and postsurgical complications increase, and vision may less likely be restored. Expedited referral to board‐certified veterinary ophthalmologists and effective client communication are key to positive patient outcomes. Note that cataracts, although common, are not the only lens‐associated pathology in companion animals. Lens luxations, both anterior and posterior, may also occur. Cats with histories of ocular trauma are more likely to develop intraocular sarcomas. This emphasizes the importance of being thorough on evaluation of the globe during physical examination so as not to miss subtle changes that could have drastic implications for the patient.
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Dogs are an ideal species to investigate phylogenetic and ontogenetic factors contributing to face recognition. Previous research has found that dogs can recognise their owner using visual information about the person’s face, presented live. However, a thorough investigation of face processing mechanisms requires the use of graphical representations and it currently remains unclear whether dogs are able to spontaneously recognise human faces in photographs. To test this, pet dogs (N = 60) were briefly separated from their owners and, to achieve reunion, they needed to select the location indicated by a photograph of their owner’s face, rather than that of an unfamiliar person concurrently presented. Photographs were taken under optimal and suboptimal (non-frontally oriented and unevenly illuminated faces) conditions. Results revealed that dogs approached their owner significantly above chance level when presented with photos taken under optimal conditions. Further analysis revealed no difference in the probability of choosing the owner between the optimal and suboptimal conditions. Dogs were more likely to choose the owner if they directed a higher percentage of looking time towards the owner’s photograph compared to the stranger’s one. In addition, the longer the total viewing time of both photos, the higher the probability that dogs chose the stranger. A main effect of dogs’ sex was also obtained, with a higher probability of male dogs choosing the owner’s photograph. This study provides direct evidence that dogs are able to recognise their owner’s face from photographs. The results imply that motion and three-dimensional information is not necessary for recognition. The findings also support the ecological valence of such stimuli and increase the validity of previous investigations into dog cognition that used two-dimensional representations of faces. The effects of attention may reflect differences at the individual level in attraction towards novel faces or in the recruitment of different face processing mechanisms.
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Background: Working dogs, such as police dogs and guide dogs, have important roles in the contemporary society by performing specific and demanding jobs. Ocular health and the maintenance of good visual acuity are imperative to strong work performance and thus human safety. Aim: The aim of this study was to assess ophthalmic abnormalities and refractive errors in police and guide dogs in Brazil. Methods: A total of 71 dogs (141 eyes) were evaluated. Ten were guide dogs and 61 were police dogs. The work performance was assessed by a questionnaire to each dog’s handler/owner. All the dogs underwent a complete ocular examination, and abnormalities were classified by condition, if they were active or inactive and if they were located within the visual axis. In addition, 62 dogs were evaluated by streak retinoscopy for refractive errors. Results: Ophthalmic abnormalities were detected in 38 (54%) dogs, of which 23 were considered inherited, 25 were considered active, and 10 were located within the visual axis. Incipient cataracts were the most prevalent abnormality. No guide dog had an abnormality within the visual axis. The most common refractive error was myopia with the median and interquartile range of −0.75 ± 0.75 diopters; among these, police dogs had −1.0 ± 0.5 diopters, whereas guide dogs +0.38 ± 0.75 diopters. Police dogs tended to be slightly myopic and guide dogs were emmetropic. Conclusion: Despite finding a considerable number of ophthalmic abnormalities and refractive error, work performance was good with no signs of visual impairment in any dog. Regular ophthalmic examinations are advised for working dogs, and an exclusion of severely affected dogs from breeding programs is recommended.
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To maintain a steady state, homeostasis, the body tightly regulates physiological processes, including the heart rate. Heart rate is the function of two opposing pathways, the sympathetic and parasympathetic nervous system, working in sync to coordinate the cardiac cycle. When heart rate rises above the reference range for what is considered normal, dogs and cats are said to be tachycardic. Tachycardia may result from cardiac or systemic dysfunction. Conditions that result in cardiac dysfunction were described in brief in Chapter 40. This chapter emphasizes systemic disturbances that lead to sinus tachycardia. Physiologic sinus tachycardia is most often the result of high sympathetic tone, as caused by stress. In addition to stress, hyperthermia and pain contribute to physiologic sinus tachycardia. By contrast, pathologic sinus tachycardia may be caused by anemia, fever, hypotension, hypovolemia, hypoxia, infectious disease, and metabolic disturbances such as hyperthyroidism. Pharmaceutical agents, such as atropine and glycopyrrolate, and an abnormally light plane of anesthesia are also contributing factors.
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The purpose of this paper is to determine the ocular echobiometry and investigate its correlation with cranial and body morphometric parameters in 50 adult Shih Tzu dogs. The echobiometric measurements of the anterior chamber (AC), vitreous chamber (VC), lens axial thickness (LTA), transverse lens thickness (LTT), and axial length of the eyeball (ALE) were obtained by two-dimensional ultrasonography. Morphometric measurements of bizygomatic distance (BDIST), frontal-occipital distance (FOD), withers height (WH), thoracic circumference (TC), and body length (BL) were also obtained. The mean of the AC depth was 2.83±0.50mm, the VC was 9.18±0.54mm, the LTA was 6.42±0.32mm and the LTT was 9.17±1.18mm, while the mean of the ALE was 18.82±0.66mm. There was no correlation between ocular echobiometric variables and cranial and body morphometric variables in adult dogs of the Shih Tzu breed, as well as no significant difference of these variables when considering gender and age of the dogs (p ≥ 0.05). Keywords: canines; biometrics; ultrasonography; ocular anatomy; ophthalmology
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Conference Paper
Medical alert dogs can save lives by alerting their human partners of impending seizures, diabetic crises, the presence of allergens, and other medical emergencies. Recent research has shown that dogs can also alert emergency services or family members through body-worn sensors. In the home, however, service dogs do not typically wear their service dog vests. In this study we show that dogs can be trained to operate touchscreens mounted in the home to alert in emergencies. We performed a home-based field study, training three medical alert dogs to perform a specific pattern of interactions with virtual objects randomly throughout the day on a cue. We showed that it is feasible for a dog to understand the task of locating the touchscreen from anywhere in the home and performing the alert interaction. We also report our training methods and challenges in creating fluency for the touchscreen alert interaction skill.
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Chapter
Service animals are trained to perform a wide variety of functions that often depend on special senses such as vision, hearing, and smell, as well as physical capabilities. To function successfully, service and working dogs must be physically fit with keen vision, sharp hearing, and high‐acuity olfaction. Before dispensing drugs that can adversely affect the special senses (olfaction, vision, and hearing) of service or working dogs, the veterinarian should be alerted so that the risks versus benefits can be assessed. Drug classes and dose levels permitted in performance animals vary widely depending on the type of competition, the governing body, the location/venue of the actual event, and the species involved. Performance‐enhancing drugs are sometimes used by owners and trainers of equine and canine athletes to gain a competitive advantage. Competitive events for animal athletes are as numerous and varied as they are for human athletes.
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Feathers perceived by humans to be vividly colorful are often presumed to be equally conspicuous to other mammals, and thus to present an enhanced predation risk. However, many mammals that prey on adult birds have dichromatic visual systems with only two types of color-sensitive visual receptors (one sensitive to ultraviolet light), rather than the three characteristic of humans and four of most birds. Thus, understanding how these predators perceive color requires quantitative visual modeling. Here, we use a combination of reflectance spectroscopy, multispectral imaging, color vision modelling and visual texture analysis to compare the visual signals available to conspecifics and to mammalian predators for multicolored feathers from the Indian peacock (Pavo cristatus) as well as red and yellow parrot feathers; we also take into account the effects of distance-dependent blurring due to visual acuity. When viewed by tetrachromatic birds against a background of green vegetation, most of the feathers studied had color and brightness contrasts similar to values previously found for ripe fruit. By contrast, when viewed by dichromat mammalian predators, the color and brightness contrasts of these feathers were only weakly detectable and often did not reach detection thresholds for typical viewing distances. We furthermore show that the peacock’s erect train has undetectable color and brightness contrasts and visual textures when photographed against various foliage backgrounds. Given the similarity of photoreceptor sensitivities and feather reflectance properties across relevant species, these findings are consistent with many feathers of similar hue being inconspicuous, and in some cases potentially cryptic, in the eyes of their mammalian predators. These results suggest that many types of colorful feathers are likely to be cryptic to mammals while providing a communication channel perceptible to birds, while emphasizing the importance of understanding diverse sensory receivers in the evolution of animal coloration.
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Visual illusions are objects that are made up of elements that are arranged in such a way as to result in erroneous perception of the objects’ physical properties. Visual illusions are used to study visual perception in humans and nonhuman animals, since they provide insight into the psychological and cognitive processes underlying the perceptual system. In a set of three experiments, we examined whether dogs were able to learn a relational discrimination and to perceive the Müller-Lyer illusion. In Experiment 1, dogs were trained to discriminate line lengths using a two-alternative forced choice procedure on a touchscreen. Upon learning the discrimination, dogs’ generalization to novel exemplars and the threshold of their abilities were tested. In the second experiment, dogs were presented with the Müller-Lyer illusion as test trials, alongside additional test trials that controlled for overall stimulus size. Dogs appeared to perceive the illusion; however, control trials revealed that they were using global size to solve the task. Experiment 3 presented modified stimuli that have been known to enhance perception of the illusion in other species. However, the dogs’ performance remained the same. These findings reveal evidence of relational learning in dogs. However, their failure to perceive the illusion emphasizes the importance of using a full array of control trials when examining these paradigms, and it suggests that visual acuity may play a crucial role in this perceptual phenomenon.
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As expressões faciais têm como finalidade estabelecer a comunicação entre os equinos. Apesar disso, também podem ser utilizadas como produto de uma situação específica e, desse modo, refletir o estado dos cavalos. Com isso, denota-se a relevância dessa linguagem corporal como indicador comportamental para avaliar diversos estados mentais positivos e negativos dos equinos. O conhecimento geral acerca das expressões faciais, entretanto, ainda é incipiente e os estudos apresentam divergências metodológicas que precisam ser compreendidas antes da replicação de tais métodos, assim como é de extrema relevância esclarecer as limitações de seu uso. Esta revisão, portanto, foi elaborada com o objetivo de apresentar e discutir os dados disponíveis na literatura no que tange às expressões faciais em cavalos, com destaque para os métodos de avaliação e as limitações no uso das características faciais. Espera-se que esta revisão possa nortear estudos futuros no desenvolvimento científico da área e contribuir para a identificação das principais lacunas.
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Working dogs trained to be detection/sniffer dogs must work closely with their human partners. Pet dogs are also often asked to perform tasks, whether in a casual context (e.g., going for a walk) or as part of more formal activity (e.g., competitive sport). For the best performance outcomes, each partner must signal well to the other, and accurately read and respond to the other's signals. As part of a larger study comparing problem-solving behavior and information use in working dogs and pet dogs, we compared the detailed responses of 40 detection dogs and 80 pet dogs to verbal signals under two conditions: when the handler was facing the dog (front-facing condition) versus when the handler had his back to the dog, while giving a verbal request (back-facing condition). We hypothesize that: (1) both groups of dogs would be more accurate and faster in response when they could see the humans’ faces and anterior bodies (front-facing condition) than in the back-facing condition; (2) dogs who did not respond immediately and correctly to the signal would exhibit behavioral signs of anxiety, uncertainty, and possibly distress, and such signals would be more common in the back-facing condition; and (3) the working dogs would be more consistent and successful as a group when compared to the pet dogs because working dogs have been specifically trained to do a job, in joint collaboration with humans who signal to them when and where to do the job and when they are successful. As such, clear signaling and response was already part of their practiced and tested daily life, and so should be reflected in their testing in this study. All testing was video recorded using the same test design and same order of tests. Neither pet nor working dogs were familiar with the test before initial testing, and neither was tested in a physical space that was familiar to them. Video analysis determined latency to response, time to completion of requested task, and identification of behaviors exhibited during the two conditions (human facing the dog/front-facing condition, or with the human's back turned to the dog/back-facing condition). Requests were given verbally using a normal tone of voice. Handlers were asked not to use hand signals. The three requests used were “sit,” “down,” and “stay”. For most comparisons, dogs were slower to respond and took longer to complete each request when they were unable to see the handler's face (back-facing condition) (all P < 0.05). The behaviors exhibited when the working dogs could not see their handler's face were largely associated with seeking further information that would allow the dog to comply with the request. This pattern of response suggests that improvements in signaling behavior and understanding for both team members can and should be made and should lead to improvements in the dogs’ welfare and better team performance. Pet dogs exhibited both information-seeking behaviors and those associated with anxiety when they could not see their owner's face, suggesting that working on efficient and accurate exchange of cues and responses would improve pet dog welfare and help to create a trusting relationship where anxiety about collaborative tasks is minimized.
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The distribution of cone photoreceptor subtypes (important for color vision and vision quality) varies widely in different carnivore species, but there have been limited studies on bear (ursid) cone distribution. A previous behavioral study suggests that American black bears (Ursus americanus) are dichromatic, indicating that they possess 2 cone subtypes, although retinal distribution of cones is unknown. The purpose of this study was to examine the subtype and topography of cones in American black bear retinas to further predict the nature of their color vision and image resolution. We studied ten eyes from 7 individual legally hunted black bears in northeastern North Carolina. Cryosections and retinal wholemounts were labeled using antibodies targeting two cone opsin subtypes: long/medium (L/M) wavelength sensitive and short (S) wavelength sensitive. Cones in fluorescent microscopy images were counted and density maps were created for retinal wholemounts. The black bear retina contains both cone subtypes and L/M cones outnumber S cones by at least 3:1, a finding confirmed in retinal frozen sections. There are higher concentrations of S cones present than typically seen in other carnivores with some evidence for co‐expression of L/M and S cones. A cone‐dense area centralis is present dorsotemporal to the optic nerve, similar to other carnivores. These results confirm that American black bears are predicted to have dichromatic vision with high acuity indicated by the presence of a dorsotemporally located area centralis. This article is protected by copyright. All rights reserved.
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In einem seit mehreren Tausend Jahren andauernden Selbstfindungsprozess erforschen Menschen die Freiheit ihres Geistes und erfreuen sich an der Erkenntnis- und Gestaltungsfähigkeit ihres Denkens (Goethe: „In euch lebe die bildende Kraft, die das Schönste, das Höchste hinauf über die Sterne das Leben trägt“). Die Grundlagen unseres geistigen Daseins haben sich dabei in Philosophie, Kunst und Religion festgeschrieben, aber Überlegungen zum Wesen der Tiere spielten eine nachgeordnete Rolle. Tiere werden entweder als Nutzmaterial betrachtet oder mit Bewunderung und mythischer Bedeutung befrachtet. Vor allem anderen aber sind sie uns fremd, und nur gelegentlich gilt ihnen unser Mitgefühl. Neben ihrer Rolle als Nahrung für Menschen scheint ihre wichtigste Bedeutung für die anthropozentrische Welt darin zu bestehen, dass sie Teil der nicht-menschlichen Natur sind. Denn die Vorstellung, dass der Mensch ein abgesondertes und privilegiertes Wesen ist und nicht zur unpersönlichen Natur der Steine, Pflanzen und Tiere zählt, gehört zu den Fundamenten des menschlichen Selbstverständnisses – zumindest in den abendländischen Kulturen. Wissenschaftliches Interesse am Wesen der Tiere, verbunden mit der Frage nach ihrem subjektiven Erleben, steht erst ganz am Ende der langen Koexistenz von Menschen und Tieren. Nach einigen vorbereitenden Einsichten im 19. Jahrhundert war die ethologische Forschung eine Neuentwicklung des 20. Jahrhunderts. Bis heute herrscht Uneinigkeit bezüglich der Frage, wie man kognitive Prozesse bei Tieren erfassen und interpretieren kann. Fast alle Konzepte zu diesem Thema waren in den letzten 100 Jahren Gegenstand wissenschaftlicher Kontroversen. Aber im scharfen Gegensatz zu früheren Zeiten ist man sich heute weitgehend darüber einig, dass Tiere ein inneres, artspezifisches Erleben haben, welches im Wechselspiel von Sinneseindrücken mit selbst erlernten Erfahrungen sowie mit einer über viele Generationen hinweg genetisch festgeschriebenen Verhaltenssteuerung das Wesen der Tiere ausmacht.
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Given humans’ habitual use of screens, they rarely consider potential differences when viewing two-dimensional (2D) stimuli and real-world versions of dimensional stimuli. Dogs also have access to many forms of screens and touchpads, with owners even subscribing to dog-directed content. Humans understand that 2D stimuli are representations of real-world objects, but do dogs? In canine cognition studies, 2D stimuli are almost always used to study what is normally 3D, like faces, and may assume that both 2D and 3D stimuli are represented in the brain the same way. Here, we used awake fMRI in 15 dogs to examine the neural mechanisms underlying dogs’ perception of two- and three-dimensional objects after the dogs were trained on either two- or three-dimensional versions of the objects. Activation within reward processing regions and parietal cortex of the dog brain to 2D and 3D versions of objects was determined by their training experience, as dogs trained on one dimensionality showed greater differential activation within the dimension on which they were trained. These results show that dogs do not automatically generalize between two- and three-dimensional versions of object stimuli and suggest that future research consider the implicit assumptions when using pictures or videos.
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Object Choice Task (OCT) studies are widely used to assess the phylogenetic and ontogenetic distribution of the understanding of communicative cues, with this understanding serving as a proxy for the discernment of communicative intentions. Recent reviews have found systematic procedural and methodological differences in studies which compare performances across species on the OCT. One such difference concerns the spatial configuration of the test set-up, specifically the distances between the two containers (inter-object distance) and the subject-experimenter distance. Here, we tested dogs on two versions of the task: a central version in which the containers were in the subjects’ direct line of vision, and a peripheral version in which the position of the containers was distal to the subject. Half of the subjects were tested with a barrier in the testing environment (as nonhuman primates are tested) and the other half without. We found that dogs tested with a barrier performed significantly better in the central version and were more likely to fail to make a choice in the peripheral version. Dogs tested without a barrier showed comparable performance on the two versions. We thus failed to find support for the distraction hypothesis in dogs. We discuss potential explanations for this, highlighting how methodological differences in the presentation of the OCT can influence outcomes in studies using this paradigm.
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This study investigated the behavioral and neural indices of detecting facial familiarity and facial emotions in human faces by dogs. Awake canine fMRI was used to evaluate dogs’ neural response to pictures and videos of familiar and unfamiliar human faces, which contained positive, neutral, and negative emotional expressions. The dog–human relationship was behaviorally characterized out-of-scanner using an unsolvable task. The caudate, hippocampus, and amygdala, mainly implicated in reward, familiarity and emotion processing, respectively, were activated in dogs when viewing familiar and emotionally salient human faces. Further, the magnitude of activation in these regions correlated with the duration for which dogs showed human-oriented behavior towards a familiar (as opposed to unfamiliar) person in the unsolvable task. These findings provide a bio-behavioral basis for the underlying markers and functions of human–dog interaction as they relate to familiarity and emotion in human faces.
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Background. This study examines how dogs observe images of natural scenes containing living creatures (wild animals, dogs and humans) recorded with eye gaze tracking. Because dogs have had limited exposure to wild animals in their lives, we also consider the natural novelty of the wild animal images for the dogs. Methods. The eye gaze of dogs was recorded while they viewed natural images containing dogs, humans, and wild animals. Three categories of images were used: naturalistic landscape images containing single humans or animals, full body images containing a single human or an animal, and full body images containing a pair of humans or animals. The gazing behavior of two dog populations, family and kennel dogs, were compared. Results. As a main effect, dogs gazed at living creatures (object areas) longer than the background areas of the images; heads longer than bodies; heads longer than background areas; and bodies longer than background areas. Dogs gazed less at the object areas vs. the background in landscape images than in the other image categories. Both dog groups also gazed wild animal heads longer than human or dog heads in the images. When viewing single animal and human images, family dogs focused their gaze very prominently on the head areas, but in images containing a pair of animals or humans, they gazed more at the body than the head areas. In kennel dogs, the difference in gazing times of the head and body areas within single or paired images failed to reach significance. Discussion. Dogs focused their gaze on living creatures in all image categories, also detecting them in the natural landscape images. Generally, they also gazed at the biologically informative areas of the images, such as the head, which supports the importance of the head/face area for dogs in obtaining social information. The natural novelty of the species represented in the images as well as the image category affected the gazing behavior of dogs. Furthermore, differences in the gazing strategy between family and kennel dogs was obtained, suggesting an influence of different social living environments and life experiences.
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The junction of the bones of the orbit, caudal maxilla and zygoma intersect to form an anatomically intricate region known as the orbitozygomaticomaxillary complex (OZMC). Given the critical role of the OZMC in the structure, function and esthetics of the skull and midface, tumors in this region present unique challenges to the oromaxillofacial surgeon. Attempts to achieve histologically clean tumor margins in a cosmetically pleasing manner requires excellent intra-operative visualization. Additionally, minimized intra-operative and post-opertive complications is of paramount importance. In this manuscript we describe a combined intra-and extraoral approach to extensive tumors of the OZMC that incorporates orbital exenteration as a technique, which allows for excellent intra-operative visualization and mitigate intra-and post-operative complications. In addition, we describe our experience utilizing the technique in five clinical cases.
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The prediction of upcoming events is of importance not only to humans and non-human primates but also to other animals that live in complex environments with lurking threats or moving prey. In this study, we examined motion tracking and anticipatory looking in dogs in two eye-tracking experiments. In Experiment 1, we presented pet dogs (N = 14) with a video depicting how two players threw a Frisbee back and forth multiple times. The horizontal movement of the Frisbee explained a substantial amount of variance of the dogs’ horizontal eye movements. With increasing duration of the video, the dogs looked at the catcher before the Frisbee arrived. In Experiment 2, we showed the dogs (N = 12) the same video recording. This time, however, we froze and rewound parts of the video to examine how the dogs would react to surprising events (i.e., the Frisbee hovering in midair and reversing its direction). The Frisbee again captured the dogs’ attention, particularly when the video was frozen and rewound for the first time. Additionally, the dogs looked faster at the catcher when the video moved forward compared to when it was rewound. We conclude that motion tracking and anticipatory looking paradigms provide promising tools for future cognitive research with canids.
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Objective To compare the grating visual acuity (VA) measured by visual evoked potentials (VEP) in phakic, aphakic, and pseudophakic Poodles. Animals studied Thirty‐six Poodle dogs aged from 4 to 14 years. Procedures Animals were allocated into three different groups according to their lens status: phakic group (n = 12), aphakic group (n = 12), and pseudophakic group (n = 12). Grating VA was measured in cycles/degree (cpd) in all animals using the electrodiagnosis system Roland RETIport® in a dark room without using any mydriatic, sedative, or anesthetic drugs. Results The mean grating VA in the phakic, aphakic, and pseudophakic groups was 5.9 ± 1.0 cpd (20/102—Snellen equivalent), 2.6 ± 0.7 cpd (20/231), and 5.2 ± 1.1 cpd (20/116), respectively. The VA from aphakic eyes was significantly lower when compared to the phakic and pseudophakic eyes (P < .05). There was no significant difference in VA between phakic and pseudophakic eyes. Conclusions The VEP is a useful tool for the evaluation of grating visual acuity in canines. The study showed that IOL implantation following phacoemulsification results in improved VA as measured by VEP compared to that of the aphakic eye and resulted in VA that was similar to that of the normal eye.
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