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The socialisation period in dog puppies is one of the most important periods determining behavioural development in dogs. Here, we aimed to test the effect of providing stimulation (beyond mere exposure) early during the socialisation period (approx. 3–6 weeks) on puppies’ behaviour. Each of 12 litters (83 puppies) of various breeds was divided into a treatment and a control group. Between 3–6 weeks, the treatment group received age-appropriate “challenge” exercises (carefully graded noise exposure, novel objects, and problem-solving tasks) four times per week (total 12 times). The control group spent the same time with the trainer, who cuddled or played with the puppies. In a behaviour test at 6–7 weeks, two of four principal components, “social-startle” and “response to novelty”, differed significantly between the groups. Treatment puppies were bolder towards the novel object, showed a reduced startle reaction, and recovered more quickly after a loud noise. Furthermore, they accomplished the problem-solving task faster and were more persistent during problem-solving than the control group. The control group showed a higher interest in a friendly stranger. It is a possibility that increased handling experienced by the control group had beneficial effects on their sociability. No long-term effects of the treatment were found, as determined by a validated dog personality questionnaire, available for 67 dogs at the age of six months. Likely, a continuation of the treatment over a longer time period would be necessary to obtain lasting effects, since the training took place only during the first third of the socialisation period.

Dogs are renowned for ‘looking back’ at humans when confronted with a problem, but it has been questioned whether this implies help-seeking or giving up. We tested 56 pet dogs from two breed groups (herding dogs and terriers) in a modified unsolvable task paradigm. One reward type (food or toy) was enclosed in a box, while the respective other reward was accessible. With both reward types, human-directed gazing in relation to the box was significantly positively correlated with interaction with the box, as long as an alternative was available. This suggests that both behaviours served to attain the unavailable reward and reflected individual motivation for the inaccessible vs the accessible reward. Furthermore, we varied whether the owner or the experimenter was responsible for handling the rewards. In the owner-responsible group, dogs rarely gazed at the experimenter. In the experimenter-responsible group, dogs preferentially directed box-related gazing (prior to or after looking at or interacting with the box) at the owner. Still, they gazed at the experimenter significantly longer than the owner-responsible group. Conversely, toy-related gazing was directed significantly more at the experimenter. Thus, dogs adjust their gazing behaviour according to the people’s responsibility and their current goal (help-seeking vs play). Gaze duration did not differ between herding dogs and terriers. We conclude that dogs use gazing at humans’ faces as a social problem-solving strategy, but not all gazing can be classified as such. Dogs’ human-directed gazing is influenced by the social relationships with the persons, situational associations, and context (unsolvable problem vs play). Supplementary Information The online version contains supplementary material available at 10.1007/s10071-021-01595-0.

The inner brow raiser is a muscle movement that increases the size of the orbital cavity, leading to the appearance of so-called ‘puppy dog eyes’. In domestic dogs, this expression was suggested to be enhanced by artificial selection and to play an important role in the dog-human relationship. Production of the inner brow raiser has been shown to be sensitive to the attentive stance of a human, suggesting a possible communicative function. However, it has not yet been examined whether it is sensitive to human presence. In the current study, we aimed to test whether the inner brow raiser differs depending on the presence or absence of an observer. We used two versions of a paradigm in an equivalent experimental setting in which dogs were trained to expect a reward; however, the presence/absence of a person in the test apparatus was varied. In the social context, a human facing the dog delivered the reward; in the non-social context, reward delivery was automatized. If the inner brow raiser has a communicative function and dogs adjust its expression to an audience, we expect it to be shown more frequently in the social context (when facing a person in the apparatus) than in the non-social context (when facing the apparatus without a person inside). The frequency of the inner brow raiser differed between the two contexts, but contrary to the prediction, it was shown more frequently in the non-social context. We further demonstrate that the inner brow raiser is strongly associated with eye movements and occurs independently in only 6% of cases. This result challenges the hypothesis that the inner brow raiser has a communicative function in dog-human interactions and suggests a lower-level explanation for its production, namely an association with eye movements.

Although free-roaming domestic dogs (FRDD) constitute the majority of the dog population worldwide, many aspects of their ecology across habitats are little known. Activity budgets by these dogs may also inform management decisions for domestic dogs in human hands. Here we collected data on the activity patterns of owned FRDD from Guatemala (n = 58) and Indonesia (n = 37), and of farm dogs (n = 11) and family dogs (n = 20) in Switzerland. The FRDD from the two countries and the Swiss farm dogs shared the similarity that although they had owners, they spent most or all of the day outside without confinement. Conversely, activity in family dogs is largely controlled by their owners. This cross-continental study thus allowed us to tease apart environmental effects on dogs’ activity from effects due to different levels of control by humans. Dogs were collared with FitBark activity trackers, which measure 3D acceleration, for 2.4–7 days. Activity for each dog was defined as the sum of BarkPoints (a continuous activity metric recorded by the FitBark tracker), calculated for each hour in the 24-hour cycle. The proportion of time resting, in ‘moderate’ and ‘high’ activity (defined by fixed thresholds of BarkPoints) over 24 h was calculated for each dog. The activity patterns of all dogs that (partly) roam freely, i.e. owned FRDD in Guatemala and Indonesia and Swiss farm dogs, showed two peaks over 24 h during 5:00–7:00 h and, less pronounced, 16:00–19:00 h. Such a bimodal activity pattern, which is also observed in other canine species, could only be detected in 45% of the family dogs. Their activity is more dependent on the owners’ daily routines and predominantly showed one high mid-day peak that often changes from day to day. Swiss dogs spent significantly more time resting and less time with ‘moderate’ activity than the owned FRDD. However, family dogs were significantly more often highly active than all other dog groups and compensated with longer resting periods. Activity decreased significantly with age, neutering and increased body condition score, whereas sex did not have any significant influence on activity. Within this study, similarities, but also differences of the activity pattern between owned FRDD and pet dogs could be revealed. Although overall activity levels of the pet dog sample fall in the range of those observed in the less controlled FRDD, it would be of interest to investigate the potential benefit of a more structured daily schedule on pet dogs in future studies.

A high proportion of pet dogs show fear-related behavioural problems, with noise fears being most prevalent. Nonetheless, few studies have objectively evaluated fear expression in this species. Using owner-provided video recordings, we coded behavioural expressions of pet dogs during a real-life firework situation at New Year’s Eve and compared them to behaviour of the same dogs on a different evening without fireworks (control condition), using Wilcoxon signed ranks tests. A backwards-directed ear position, measured at the base of the ear, was most strongly associated with the fireworks condition (effect size: Cohen’s d = 0.69). Durations of locomotion (d = 0.54) and panting (d = 0.45) were also higher during fireworks than during the control condition. Vocalisations (d = 0.40), blinking (d = 0.37), and hiding (d = 0.37) were increased during fireworks, but this was not significant after sequential Bonferroni correction. This could possibly be attributed to the high inter-individual variability in the frequency of blinking and the majority of subjects not vocalising or hiding at all. Thus, individual differences must be taken into account when aiming to assess an individual’s level of fear, as relevant measures may not be the same for all individuals. Firework exposure was not associated with an elevated rate of other so-called ‘stress signals’, lip licking and yawning.

Reinforcer effectiveness refers to the reinforcer’s ability to control the subject’s target behaviour and is therefore critical to training success. Yet animals’ preferences, and the effectiveness of different rewards to function as reinforcers, are often assumed without scientific investigation. Here we explored the influence of reward quality, quantity and changes in reward value on motivation in domestic dogs. Subjects were trained to traverse a runway for a food reward. In Study 1, the quantity of food was varied (1 vs 5 pieces of dry food), while in Study 2, food quality was varied (1 piece of sausage vs 1 piece of dry food). Dogs were tested in two conditions (counterbalanced). In the unshifted condition, they received the low value reward in all of ten trials; in the shifted condition, reward value was altered (high value: trials 1–4 and 9–10; low value: trials 5–8). While preliminary preference tests had confirmed the relative value of the presumed high and low value rewards for both quantity and quality, dogs' responses in the runway task differed between the quality and quantity studies. Dogs ran significantly faster for the higher quality food compared to the lower quality food, confirming greater reinforcer effectiveness of the preferred food type. In contrast, there was no significant effect of food quantity on running speed at any stage. Higher quality rewards therefore appear to entail greater incentive motivation in dogs than a greater quantity of a lower value reward, with reward-specific habituation needing to be considered.

When determining an animal’s food preference based on comparative consumption, a major problem is the potential for individuals to over-eat, rendering subjects unavailable for subsequent tests as well as exposing them to potentially adverse health implications. Here, we explored alternative, simple and quick ways of assessing food preference that involved only minimal training and avoided satiation. In Study 1, we investigated whether behaviour directed towards inaccessible food predicted consummatory choice. Following a prime with small quantities of two types of food of putatively different quality, 18 pet dogs were concurrently presented with the same two food types in a manner that they could see and smell, but not physically access. Time spent investigating the two inaccessible food types was measured. Subsequently, the dogs were given the opportunity to consume the same two food types but this time in a restricted-intake consummatory test: two puzzle feeders were presented simultaneously, each containing 18 pieces of one of the two food types. The proportion of food types making up the first 18 pieces consumed was recorded. Subjects showed a highly significant preference for the food type predicted to be of higher value in both the non-consummatory and the consummatory test. Moreover the proportion of time spent investigating the two food types in the non-consummatory test was very similar to the proportion of the two food types consumed from the puzzle feeders, demonstrating validity of both test methods. There are, however, some limitations to the consummatory test, in particular that it can only be valid if the two food types to be compared are of similar ease to extract from the boards. To assess the generalizability of the non-consummatory food preference test, in Study 2 we investigated test-retest reliability in 20 dogs, as well as consistency of preferences across populations by comparing 20 owned pet dogs and 25 dogs housed in rescue shelters. Findings were consistent across repetitions of the test as well as across the two test populations. Thus, relative food preference could be confidently and reliably inferred from behaviour during a non-consummatory exposure. The ease and speed of use, the lack of training required and the avoidance of satiation make this an ideal test for determining food preference.

Simple Summary The majority of dogs and cats are fearful during veterinary visits, and some individuals may show aggression as a result. We review ways to avoid negative experiences and promote positive emotions in animals visiting the veterinarian. Whenever an animal is in the practice, the veterinary team should endeavour to make the visit as pleasant as possible, by using non-threatening body language and by creating positive associations. High-value food (unless an animal needs to be fasted) or toys should be used generously throughout the visit. In the interaction with the animals, low-stress handling methods, brief pauses and adjusting the procedure based on the animal’s body language help them to feel secure. Distractions can be used to minimise perceived pain such as from injections. If a known painful area needs to be treated, pain killers are advised. For animals that are very fearful, several medication options are available that can be given prior to the veterinary visit to help them with their fears. With reward-based training, animals can learn to accept veterinary procedures. A stress-free veterinary visit benefits all involved parties—the animals, their owners, as well as the veterinary team. Abstract A high proportion of dogs and cats are fearful during veterinary visits, which in some cases may escalate into aggression. Here, we discuss factors that contribute to negative emotions in a veterinary setting and how these can be addressed. We briefly summarise the available evidence for the interventions discussed. The set-up of the waiting area (e.g., spatial dividers; elevated places for cat carriers), tailoring the examination and the treatment to the individual, considerate handling (minimal restraint when possible, avoiding leaning over or cornering animals) and offering high-value food or toys throughout the visit can promote security and, ideally, positive associations. Desensitisation and counterconditioning are highly recommended, both to prevent and address existing negative emotions. Short-term pain from injections can be minimised by using tactile and cognitive distractions and topical analgesics, which are also indicated for painful procedures such as ear cleanings. Recommendations for handling fearful animals to minimise aggressive responses are discussed. However, anxiolytics or sedation should be used whenever there is a risk of traumatising an animal or for safety reasons. Stress-reducing measures can decrease fear and stress in patients and consequently their owners, thus strengthening the relationship with the clients as well as increasing the professional satisfaction of veterinary staff.

Recently, there has been a move towards positive reinforcement using food rewards in animal training. By definition, rewards function as reinforcers if they increase or maintain the frequency of behaviour that they follow. However, in operant conditioning tasks animals frequently show systematic changes in performance – in particular a reduction in responding over time. One suggested strategy to avoid such performance decrements is to provide a variety of food rewards, rather than the same food reward in all trials. The enhancement of appetitive behaviour and consumption by reward variation is referred to as ‘variety effect’. We investigated whether dogs preferred a variable or a constant food reward in a concurrent two-choice test. Of 16 dogs, six subjects showed a significant preference for the varied food reward and six for the constant food reward, while four dogs exhibited no significant preference for either option. At the group level, there was a significant effect of block: preference for the varied food reward increased across six blocks of ten trials each. Thus, although some individuals may prefer a single, favourite food reward in the short term, introducing variation in reward types may maintain dogs’ motivation in operant tasks over a longer time period.

[This corrects the article DOI: 10.1371/journal.pone.0195448.].

Visible and invisible displacement tasks have been used widely for comparative studies of animals' understanding of object permanence, with evidence accumulating that some species can solve invisible displacement tasks and, thus, reach Piagetian stage 6 of object permanence. In contrast, dogs appear to rely on associative cues, such as the location of the displacement device, during invisible displacement tasks. It remains unclear, however, whether dogs, and other species that failed in invisible displacement tasks, do so because of their inability to form a mental representation of the target object, or simply because of the involvement of a more salient but potentially misleading associative cue, the displacement device. Here we show that the use of a displacement device impairs the performance of dogs also in visible displacement tasks: their search accuracy was significantly lower when a visible displacement was performed with a displacement device, and only two of initially 42 dogs passed the sham-baiting control conditions. The negative influence of the displacement device in visible displacement tasks may be explained by strong associative cues overriding explicit information about the target object's location, reminiscent of an overshadowing effect, and/or object individuation errors as the target object is placed within the displacement device and moves along a spatiotemporally identical trajectory. Our data suggest that a comprehensive appraisal of a species' performance in object permanence tasks should include visible displacement tasks with the same displacement device used in invisible displacements, which typically has not been done in the past.

String pulling tasks are commonly used to investigate recognition of means-end connections. Previous studies suggested that dogs base their choice on proximity rather than connectivity (Osthaus, Lea, & Slater, 2005), nonetheless, dogs performed successfully in the related support problem (Range, Hentrup, & Viranyi, 2011). To reinvestigate dogs' means-end understanding, we tested 34 Border collies in string pulling tasks in which the proximity of the reward to the connected string's end was varied. First, subjects were presented with a four-string task (four parallel perpendicular strings, one baited, with the reward in line with the correct string's end). Dogs that performed above chance in this task were tested with a curved string task, involving one straight and one curved string. When the reward was attached to the curved string, it was equidistant from both strings' ends so that choosing by proximity was not possible. Although group level performance was significantly above chance, only three of 20 dogs met criterion individually, of which one dog subsequently solved a broken string task upon its first presentation. However, the dogs seemed to be unable to overcome their proximity bias in a parallel diagonal string task where proximity of the unconnected string's end to the reward was misleading. We conclude that although dogs may not demonstrate means-end understanding spontaneously, some can learn to pay attention to connectivity when proximity is not a confounding factor. This study supports the notion that animals may apply several alternative strategies to solve physical problems, which are influenced by the test-setup.

A wealth of comparative data has been accumulated over the past decades on how animals acquire and use information about the physical world. Domestic dogs have typically performed comparably poorly in physical cognition tasks, though in a recent study Kundey et al. (Anim Cogn 13:497-505, 2010) challenged this view and concluded that dogs understand that objects cannot pass through solid barriers. However, the eight subjects in the study of Kundey et al. may have solved the task with the help of perceptual cues, which had not been controlled for. Here, we tested dogs with a similar task that excluded these cues. In addition, unlike the set-up of Kundey et al., our set-up allowed the subjects to observe the effect of the solid barrier. Nevertheless, all 28 subjects failed to solve this task spontaneously and showed no evidence of learning across 50 trials. Our results therefore call into question the earlier suggestion that dogs have, or can acquire, an understanding of the solidity principle.

In order to assess dogs’ personality changes during ontogeny, a cohort of 69 Border collies was followed up from six to 18–24 months. When the dogs were 6, 12, and 18–24 months old, their owners repeatedly filled in a dog personality questionnaire (DPQ), which yielded five personality factors divided into fifteen facets. All five DPQ factors were highly correlated between the three age classes, indicating that the dogs’ personality remained consistent relative to other individuals. Nonetheless, at the group level significant changes with age were found for four of the five DPQ factors. Fearfulness, Aggression towards People, Responsiveness to Training and Aggression towards Animals increased with age; only Activity/Excitability did not change significantly over time. These changes in DPQ factor scores occurred mainly between the ages of 6 and 12 months, although some facets changed beyond this age. No sex differences were found for any of the tested factors or facets, suggesting that individual variation in personality was greater than male/female differences. There were significant litter effects for the factors Fearfulness, Aggression towards People and Activity/Excitability, indicating either a strong genetic basis for these traits or a high influence of the shared early environment. To conclude, from the age of six months, consistency in personality relative to other individuals can be observed in Border collies. However, at the group level, increases in fearful and aggressive behaviours occur up to 12 months and for some traits up to two years, highlighting the need for early interventions. Follow-up studies are needed to assess trajectories of personality development prior to six months and after two years, and to include a wider variety of breeds.

Based on their high sociability and their capabilities in social cognition, we should consider that dogs experience rich emotions in the social domain. I discuss the importance of dog-human attachment and some of the controversial evidence for so-called secondary emotions, which leaves many questions to answer.

Humans in a negative emotional state are more likely to judge ambiguous stimuli as negative. In recent years, similar judgement biases have been found in some non-human animals that were exposed to long-term or short-term treatments aimed at influencing their affective states. Here we tested pet dogs in the presence and absence of their owners in a judgement bias test with an established go/no-go procedure. Even though owner absence is thought to induce a state of anxiety in dogs that have formed an attachment bond with their primary caretakers, we found no difference between the dogs' responses to ambiguous stimuli in the presence or absence of their owners. This result may be explained by the absence of anxiety in dogs that are accustomed to brief periods of separation from their owners, or by a sensitivity limit of the customary judgement bias tests in non-human animals when only a moderate, short-term state of anxiety is induced. In addition, we found significant differences between individuals and populations in the responses to ambiguous stimuli, which give impetus for further research.

Measures that are likely to increase sociability in dog puppies, such as appropriate socialisation, are considered important in preventing future fear or aggression related problems. However, the interplay between sociability and conflict behaviour has rarely been investigated. Moreover, while many studies have addressed aggression in domestic dogs, alternative, non-aggressive conflict resolution strategies have received less scientific attention. Here we tested 134 Border collie puppies, aged 40-50 days, in a personality test which included friendly interactions with an unfamiliar person, exposure to a novel object, and three brief restraint tests. Considering the latter to be mild ‘conflict’ situations, we analysed whether the puppies’ behaviour in the restraint tests was related to their sociability or to their boldness towards the novel object. Strategies employed by the puppies during restraint tests included trying to interact socially with the experimenter, remaining passive, and attempting to move away. In line with findings from humans and goats, puppies scoring high on sociability were more likely to adopt an interactive conflict resolution strategy, while those with low sociability scores tended to react passively. In contrast, avoidance behaviours were unrelated to sociability, possibly reflecting inconsistency in the flight strategy in dogs. Boldness towards a novel object was not related to sociability or to puppies’ reactions in restraint tests. This is one of the first studies to demonstrate a link between sociability and conflict resolution strategies in non-human animals.

s / Journal of Veterinary Behavior 8 (2013) e27ee46 e34 Sixty day after testing all dogs were assessed in a blinded manner by repeating the DMA. Data were analyzed using a Wilcoxon test using an a priori value of P < 0.05 as a measure of significance. Dogs of the experimental group statistically increased their scores after the problem solving sessions (16.29 vs 21.58; W 1⁄4 91.0; P < 0.022). Scores of the control groups did not show any change. These preliminary data suggest that problem solving sessions may be effective in reducing fear.

s 81 people. To measure emotion recognition, the computer test VERT-K (Vienna Emotion Recognition Tasks) was used to identify the emotion recognition capacity of the participants before and after the twelve weeks training. Statistical analysis included explorative procedures t-tests with repeated measures to analyze the significant changes and effect size calculations. Results show that the highest changes with relevant effect sizes in the adult group concern the correct identification of anger (t (15)522.058, P5 0.028, d5 0.75), neutral facial expression (t (15)522.535, P5 0.011, d5 0.93) as well as the overall number of correctly identified facial expressions (t(15)522.340, P50.017, d50.88). In addition, a decrease in reaction times was documented. The children significantly increased their capacity regarding the recognition of neutral facial expression (t (18)522,412, P5 0.014, d5 0.80), the overall number of correctly identified expressions (t (18) 5 21.950, P5 0.034, d5 0.65) as well as the basic emotions grief (t (18) 5 21.660, P 5 0.057, d 5 0.55) and disgust (t (18) 5 21.656, P 5 0.057, d 5 0.55). Reaction time also decreased significantly. The participants identified more emotions correctly and decreased their reaction time significantly even though ‘‘only’’dog facial/emotional expression is part of the program.