Anthropogenic noise generated by vessel traffic is a pervasive source of disturbance in marine environments, overlapping with the hearing-sensitive range of many fish species, including the European sea bass (Dicentrarchus labrax). Although behavioural responses to the specific nature of the noise have been documented, the influence of stimulus familiarity and the temporal dynamics of noise onset on these responses remains poorly explored. This study investigated how familiarity with the stimulus and onset abruptness shape acute behavioural responses to noise in European sea bass. Groups of five fishes were exposed to one of different acoustic conditions combining familiarity (familiar vs. unfamiliar boat noise) and onset profile (progressive vs. sudden), or to background noise only. Behavioural data were collected on videos across five time-intervals. Results showed that progressive familiar noise produced minimal behavioural disruption, consistent with habituation to stimuli encountered at the rearing facility. Sudden onset consistently elicited stronger acute reactions than progressive onset, and familiarity moderated both the magnitude of those reactions and the speed of recovery. Familiarity also influenced the quality of the response: sudden familiar noise triggered organized, coordinated group behaviour with rapid return to baseline, while sudden unfamiliar noise led to persistent disruption of social synchronicity, pointing to a shift toward more individualistic, less predictable responses. These findings demonstrate that familiarity and onset abruptness interact to determine both the magnitude and the quality of behavioural responses, shifting patterns from organized, group-level reactions to individualized, startle-like, disorganized responses as novelty and suddenness increase. Condition-specific fluctuations were also observed in side-tilting, suggesting a potential role of this behaviour as a displacement activity and as a component of welfare assessment in farmed fish. Taken together, these results indicate that temporal dynamics and prior acoustic experience are critical determinants of the impact of noise. The findings of this study can help define practical strategies to minimize noise-related distress and promote welfare in aquaculture settings.

Three-dimensionality perception relies on the integration of various depth cues, with monocular pictorial cues playing a key role in two-dimensional representations. Previous research indicates that dogs are sensitive to a combination of shading and linear perspective when perceiving three-dimensionality, yet the individual contributions of these cues remain unclear. The aim of the present study was to disentangle the specific contribution of shading and linear perspective in promoting three-dimensional perception in dogs. In a series of four experiments involving 120 dogs, subjects were presented with a ball rolling on an apparatus and either falling inside a real hole (control condition) or keeping rolling over a depicted hole (test condition). Experiments 1 and 2 assessed the individual contribution of linear perspective and shading in dogs’ perception of three-dimensionality; Experiment 3, as a replica of previous findings, investigated the combination of both cues; Experiment 4 explored the role of more intense shading. In a violation of expectation paradigm, dogs showed no sensitivity to the pictorial cue of linear perspective or low shading level alone. Conversely, the combination of linear perspective and shading, as well as intense shading alone, successfully elicited three-dimensional perception. These results confirm that dogs can successfully integrate multiple pictorial cues to perceive three-dimensionality from two-dimensional stimuli. The perception of three-dimensionality can also occur through single cues, but only if the cue is sufficiently intense, at least in the case of shading.

Serial dependence is a recently described phenomenon by which the perceptual evaluation of a stimulus is biased by a previously attended one. By integrating stimuli over time, serial dependence is believed to ensure a stable conscious experience. Despite increasing studies in humans, it is unknown if the process occurs also in other species. Here, we assessed whether serial dependence occurs in dogs. To this aim, dogs were trained on a quantity discrimination task before being presented with a discrimination where one of the discriminanda was preceded by a task-irrelevant stimulus. If dogs are susceptible to serial dependence, the task-irrelevant stimulus was hypothesized to influence the perception of the subsequently presented quantity. Our results revealed that dogs perceived the currently presented quantity to be closer to the one presented briefly before, in accordance with serial dependence. The direction and strength of the effect were comparable to those observed in humans. Data regarding dogs’ attention during the task suggest that dogs used two different quantity estimation mechanisms, an indication of a higher cognitive mechanism involved in the process. The present results are the first empirical evidence that serial dependence extends beyond humans, suggesting that the mechanism is shared by phylogenetically distant mammals.

Prior research has demonstrated that animal vocalizations and music can elicit emotional responses in dogs, but their preferences for different acoustic stimuli remain underexplored. This study aimed to develop a methodology to assess dogs’ preferences and behavioral reactions to various acoustic stimuli and examine the role of familiarity in shaping these responses. In the first experiment, 90 pet dogs were exposed to one of six types of sound stimuli: conspecific agonistic vocalizations, conspecific vocalizations recorded in positive contexts, classical music, relaxing music, dog-directed speech, and neutral background noise. The setup involved a room virtually divided into two areas, in which the dog could freely move. Sounds were turned on or off, depending on which of the two zones the dog was in, thereby giving subjects the possibility to choose whether to be exposed to the sound or not. Preferences were determined by relative amount of time spent in the sound versus quiet zone and behaviors were analyzed for emotional indicators. Dogs actively avoided agonistic vocalizations exhibiting increased attention-seeking behaviors toward their owners. No distinct preferences or aversions emerged for the other stimuli, although conspecific vocalizations in positive contexts and dog-directed speech elicited dogs’ attention. Both types of music resulted in lower attention towards the sound compared to the neutral condition. In Experiment 2, the same procedure was used with 20 dogs, half of whom were routinely exposed to classical music at home, to test whether familiarity with classical music affected behavioral responses and preferences. Although no significant behavioral changes or preferences for classical music were observed, dogs with prior exposure spent twice as much time in the sound zone compared to those without, suggesting enhanced likability due to familiarity. These dogs also exhibited more relaxed behaviors, indicating that familiarity may influence emotional responses.Overall, the study introduces a novel approach for evaluating dogs' preferences for acoustic stimuli. It revealed that none of the stimuli allegedly inducing positive emotions led to a clear preference. However, behavioral data suggest that familiarity can enhance the likability of specific sounds. These findings highlight the need for further investigation into how different soundscapes influence dogs' emotions and behavior over time, and whether dogs may inherently prefer silence. Moreover, the results underscore the importance of carefully considering acoustic enrichment strategies, particularly the role of familiarization in shaping dogs' responses to their auditory environment.

Predatory behaviour is a relevant part of the behavioural repertoire of dogs, which often entails negative or desirable implications, depending on the context and target to which it is directed. It is also considered one of the most characterising aspects of breed-specific behaviour. Despite its relevance, there is surprisingly little scientific knowledge about the topic. In the present study we sought to develop an ethogram of the predatory sequence of dogs, with the aim of providing a sufficiently general structure to be applicable to dogs at large, without eluding peculiar aspects of the species' specific behaviour. Sixty videos of dogs of different breeds expressing predatory acts, including both videos obtained from public internet repositories and videos made on purpose, were described in detail by two different observers. From descriptions, a general sequence was identified, consisting of four functional phases, i.e. search, approach, chase and bite. The descriptions of the behaviours included in each phase were organised into three levels, characterised by different levels of detail and focusing on different aspects of the behaviour. When appropriate, these descriptions highlighted differences in behaviour expressed by dogs belonging to different working groups. The ethogram proposed in the present paper could represent a useful starting point for improving knowledge about the predatory behaviour of dogs and answering relevant questions about both its evolution and ontogeny.

The perception of tridimensionality is elicited by binocular disparity, motion parallax, and monocular or pictorial cues. The perception of tridimensionality arising from pictorial cues has been investigated in several non-human animal species. Although dogs can use and discriminate bidimensional images, to date there is no evidence of dogs' ability to perceive tridimensionality in pictures and/or through pictorial cues. The aim of the present study was to assess the perception of tridimensionality in dogs elicited by two pictorial cues: linear perspective and shading. Thirty-two dogs were presented with a tridimensional stimulus (i.e., a ball) rolling onto a planar surface until eventually falling into a hole (control condition) or until reaching and rolling over an illusory hole (test condition). The illusory hole corresponded to the bidimensional pictorial representation of the real hole, in which the pictorial cues of shading and linear perspective created the impression of tridimensionality. In a violation of expectation paradigm, dogs showed a longer looking time at the scene in which the unexpected situation of a ball rolling over an illusory hole occurred. The surprise reaction observed in the test condition suggests that the pictorial cues of shading and linear perspective in the bidimensional image of the hole were able to elicit the perception of tridimensionality in dogs.

There is a growing interest in performing playback experiments to understand which acoustical cues trigger specific behavioral/emotional responses in dogs. However, very limited studies have focused their attention on more basic aspects of hearing such as sensitivity, i.e., the identification of minimal intensity thresholds across different frequencies. Most previous studies relied on electrophysiological methods for audiograms for dogs, but these methods are considered less accurate than assessments based on behavioral responses. To our knowledge, only one study has established hearing thresholds using a behavioral assessment on four dogs but using a method that did not allow potential improvement throughout the sessions. In the present study, we devised an assessment procedure based on a staircase method. Implying the adaptation of the assessed intensity on the dogs’ performance, this approach grants several assessments around the actual hearing threshold of the animal, thereby increasing the reliability of the result. We used such a method to determine hearing thresholds at three frequencies (0.5, 4.0, and 20.0 kHz). Five dogs were tested in each frequency. The hearing thresholds were found to be 19.5 ± 2.8 dB SPL at 0.5 kHz, 14.0 ± 4.5 dB SPL at 4.0 kHz, and 8.5 ± 12.8 dB SPL at 20.0 kHz. No improvement in performance was visible across the procedure. While the thresholds at 0.5 and 4.0 kHz were in line with the previous literature, the threshold at 20 kHz was remarkably lower than expected. Dogs’ ability to produce vocalization beyond 20 kHz, potentially used in short-range communication, and the selective pressure linked to intraspecific communication in social canids are discussed as potential explanations for the sensitivity to higher frequencies.

The aim of this study is to develop an Italian translation of the 100-item Canine Behavioral Assessment and Research Questionnaire (C-BARQ) version and to validate its psychometric properties, in order to facilitate systematic, large-scale studies on dog behavior for Italian-speaking dog owners. A total number of 803 responses by dog owners were collected online. Using the Principal Axis Method and Common Factor Analysis with Quartimin oblique rotation (p < 0.05), a factorial structure was found including 13 factors composed of 62 items and explaining 53.5% of the total variance. Eight factors showed high reliability (Cronbach’s alpha > 0.70), namely: stranger-directed aggression/fear, dog-directed fear, owner-directed aggression, separation-related behavior, chasing, dog-directed aggression, attachment/attention seeking, and elimination problems. Three factors were slightly under the threshold and two had only modest reliability (non-social fear, energy level, touch sensitivity, excitability and trainability). A potential explanation for factors with low reliability is that the composing items do not describe behaviors resulting from homogeneous stimuli or situations. Although our factorial structure resembled in most respects that of the most recently published Canadian version, some important exceptions are present regarding dog rivalry, intraspecific aggression, fear/aggression towards strangers, touch sensitivity and chewing inappropriate objects. Such differences may be due to demographic and/or cultural differences between the sampled populations. Overall, the results suggest that a 62-item Italian C-BARQ can be reliably used in studies on dog behavior.

A recent paper by Pepperberg, Learning & Behavior , 51 , 5–6, ( 2023 ) enquires about the validity of the finding that dogs are susceptible to the Kanizsa’s triangle illusion, reported by Lõoke and coauthors (Lõoke et al., Animal Cognition , 25 , 43–51, 2022 ). Here we elaborate on the matter, providing both theoretical considerations and further data, supporting the soundness of our previous conclusions.

Dogs can recognize conspecifics in cross-modal audio-video presentations. In this paper, we aimed at exploring if such capability extends to the recognition of cats, and whether it is influenced by exposure to these animals. To reach our aim, we enrolled 64 pet dogs. Half of the dogs were currently living with cats, while the rest had never been living with cats, nor were at the time of the experiment. All dogs underwent a cross-modal violation of expectancy experiment, where they were presented with either a cat or a dog vocalization, followed by a video of either species on a blank background. The result revealed that dogs did not exhibit a surprise reaction towards the incoherent stimuli of a cat vocalization and a dog video or vice-versa, implying that they had not recognized the stimuli portraying cats. The pattern of results did not differ between dogs living or not with cats, implying that exposure to a limited number of cats, however, prolonged, is not sufficient to grant dogs with the ability to recognize them on audio-video presentations. We propose that the lack of recognition could be due to the small number of individual cats the dogs are regularly exposed to, or to the possible lack of early exposure to cats during the socialization phase.

Visually tracking a moving object, even if it becomes temporarily invisible, is an important skill for animals living in complex environments. However, this ability has not been widely explored in dogs. To address this gap of knowledge and understand how experience contributes to such ability, we conducted two experiments using a violation of expectation paradigm. Dogs were shown an animation of a ball moving horizontally across a screen, passing behind an occluder, and reappearing with a timing that was faster, slower or congruent with its initial speed. In the first experiment, dogs ( N = 15) were exposed to the incongruent conditions without prior experience; while in the second experiment, dogs ( N = 37) were preliminarily exposed to the congruent stimulus. Dogs of the first experiment did not exhibit a surprise effect, as measured by latency to look away from the expected stimulus presentation area, in response to the incongruent conditions, suggesting they had not formed an expectation about the timing of reappearance. However, their latency to orient towards the reappearing ball depended on the condition, suggesting they were able, to some extent, to visually keep track of the stimulus’ trajectory. Dogs of the second experiment were surprised when the ball stayed behind the occluder longer than expected, but showed no difference in latency to orient across conditions. This suggests they had overcome the visual tracking mechanism and had formed expectations about the timing of reappearance. In conclusion, dogs seem to use a low-level mechanism to keep visual track of a temporarily disappearing moving object, but experience is required to make expectation about its trajectory.

Environmental enrichment is a crucial element for the promotion of welfare of animals kept under human care. While a large variety of environmental enrichments has been proposed and studied for terrestrial animals, including a growing area represented by acoustical enrichment such as music, the same is not true for marine mammals. The purpose of this study was to evaluate the ability of classical music to act as an enrichment for bottlenose dolphins under human care (Tursiops truncatus); its effect on the dolphins' behaviour were compared with that of a less complex auditory stimulus (rain sound), another novel, but visual enrichment (slideshow of photographs), and an already known form of enrichment (floating objects). The study was conducted on 8 dolphins housed in a dolphinarium in Riccione, Italy. Enrichments were provided for 20 min/day, on 7 days for each enrichment type. Their effect was evaluated by observing changes in behaviours expressed during or shortly after the provision of the enrichment. Some effects were unspecific, being shared by most, or all types of enrichment, including an increase of activity levels and synchronous swimming. However, only classical music was able to increase several social affiliative behaviours both during its presentation and after its removal. The results indicate that classical music has positive effects on behaviour, that qualify it as an effective environmental enrichment for dolphins in this context. Some aspects remain to be elucidated, including the mechanisms by which music exerts its effects, and how specific to classical music the latter are. Nonetheless, the specificity of effects on social behaviour suggest that classical music could be particularly useful when an improvement in social behaviours is needed.

The minimum audible angle (MAA), defined as the smallest detectable difference between the azimuths of two identical sources of sound, is a standard measure of spatial auditory acuity in animals. Few studies have explored the MAA of dogs, using methods that do not allow potential improvement throughout the assessment, and with a very small number of dog(s) assessed. To overcome these limits, we adopted a staircase method on 10 dogs, using a two-forced choice procedure with two sound sources, testing angles of separation from 60° to 1°. The staircase method permits the level of difficulty for each dog to be continuously adapted and allows for the observation of improvement over time. The dogs’ average MAA was 7.6°, although with a large interindividual variability, ranging from 1.3° to 13.2°. A global improvement was observed across the procedure, substantiated by a gradual lowering of the MAA and of choice latency across sessions. The results indicate that the staircase method is feasible and reliable in the assessment of auditory spatial localization in dogs, highlighting the importance of using an appropriate method in a sensory discrimination task, so as to allow improvement over time. The results also reveal that the MAA of dogs is more variable than previously reported, potentially reaching values lower than 2°. Although no clear patterns of association emerged between MAA and dogs’ characteristics such as ear shape, head shape or age, the results suggest the value of conducting larger-scale studies to determine whether these or other factors influence sound localization abilities in dogs.

The ability to complete partially missing contours is widespread across the animal kingdom, but whether this extends to dogs is still unknown. To address this gap in knowledge, we assessed dogs’ susceptibility to one of the most common contour illusions, the Kanizsa’s triangle. Six dogs were trained to discriminate a triangle from other geometrical figures using a two-alternative conditioned discrimination task. Once the learning criterion was reached, dogs were presented with the Kanizsa’s triangle and a control stimulus, where inducers were rotated around their centre, so as to disrupt what would be perceived as a triangle by a human observer. As a group, dogs chose the illusory triangle significantly more often than control stimuli. At the individual level, susceptibility to the illusion was shown by five out of six dogs. This is the first study where dogs as a group show susceptibility to a visual illusion in the same manner as humans. Moreover, the analyses revealed a negative effect of age on susceptibility, an effect that was also found in humans. Altogether, this suggests that the underling perceptual mechanisms are similar between dogs and humans, and in sharp contrast with other categories of visual illusions to which the susceptibility of dogs has been previously assessed.

In humans, numerical estimation is affected by perceptual biases, such as those originating from the spatial arrangement of elements. Different animal species can also make relative quantity judgements. This includes dogs, who have been proposed as a good model for comparative neuroscience. However, dogs do not show the same perceptual biases observed in humans. Thus, the exact perceptual/cognitive mechanisms underlying quantity estimations in dogs and their degree of similarity with humans are still a matter of debate. Here we explored whether dogs are susceptible to the connectedness illusion, an illusion based on the tendency to underestimate the quantity of interconnected items. Dogs were first trained to choose the larger of two food arrays. Then, they were presented with two arrays containing the same quantity of food, of which one had items interconnected by lines. Dogs significantly selected the array with unconnected items, suggesting that, like in humans, connectedness determines underestimation biases, possibly disrupting the perceptual system's ability to segment the display into discrete objects. The similarity in dogs' and humans' susceptibility to the connectedness, but not to other numerical illusions, suggests that different mechanisms are involved in the estimation of quantity of stimuli with different characteristics.

The ability to perceive motion is a fundamental property of the visual system, and one of its most basic aspects is the ability to discriminate moving objects from motionless ones, for example, motion detection. Velocity thresholds represent the minimum rate of displacement over time unit that an animal is able to perceive as movement, any slower motion being not discriminable from a still object. Although such topic has grabbed the attention of scientists already at the beginning of the 20th century, the interest has waned in time, and velocity thresholds have thus far been assessed in only a handful of species. Thresholds for pigeons Columba livia, rats Rattus norvegicus, and cats Felis catus fall in an approximate range of 1–10 deg/s. (Since perceived linear speed depends on the distance between the moving stimulus and the observer, angular speed [i.e., angle of the observer’s field of view/unit time], which is distance invariant, is the preferred unit in the speed perception literature) (Hawley and Munn 1933; Pasternak and Merigan 1980; Martinoya et al. 1983). Thresholds <1 deg/s are only reported for nonhuman primates (Carpenter and Carpenter 1958), falling to under 0.1 deg/s for adult humans (Snowden and Kavanagh 2006). Dogs’ visual processing received growing interest in recent years (Byosiere et al. 2018). Within the area of motion perception, the topic that has received more attention is certainly the perception of biological motion (Delanoeije et al. 2020 and references therein). Fewer studies have explored more basic aspects of dogs’ motion perception. Very early work suggests that dogs could recognize moving objects from a distance of 800 to 900 m, but could recognize stationary objects only at a distance of 500–600 m, which would imply a particular aptness at detecting moving entities by dogs. More recently, however, dogs’ ability to detect motion as a function of the stimulus coherence has been explored (Kanizsár et al. 2017). The latter represents the proportion of local constituents in a visual scene, which moves with the same direction and speed. Dogs were found to require an average of 42% of coherence to discriminate a random-dot display from 1 with a coherence of 0%. This indicates a poor ability to detect coherent motion, especially when compared with humans’ 5% coherence threshold. Moreover, although such ability can be improved through experience, thresholds in dogs are higher than those reported for humans (Kanizsár et al. 2018). Therefore, the notion that dogs could be particularly apt to perceive motion was not supported, at least in terms of coherence threshold. To our knowledge, no one has explored what are the perceptual limits of dogs in terms of motion velocity thresholds. The aim of this study was therefore to determine the minimum velocity that dogs can perceive as motion. To this aim, we employed a modified method of limits, whereby dogs (N1⁄46) were first trained to discriminate a static random-dot display from 1 where dots moved at a clearly perceivable velocity. Once dogs reached a discrimination accuracy of at least 90% over 6 consecutive 20-presentation sessions, subjects underwent a series of descending and ascending assessment, where the speed of dots in the discriminandum random-dot display was systematically varied. Methodological details can be found in the Supplementary Materials. All the 6 enrolled dogs reached the learning criterion in the training phase. The mean number of sessions to reach such criterion was 23.3 6 11.3, ranging from 13 to 42. The mean value and the distribution of thresholds obtained in each of the 4 assessments are presented in Figure 1. Individual dogs’ thresholds are presented in the Supplementary Material. The mean individual velocity threshold ranged between 0.26 deg/s and 1.24 deg/s. The overall mean velocity threshold in our sample was of 0.76 6 0.38 deg/s. Mean velocity thresholds were not correlated with the length of the training

The functional roles of the Caudate nucleus (Cd) are well known. Selective Cd lesions can be found in neurological disorders. However, little is known about the dynamics of the behavioral changes during progressive Cd ablation. Current stereotactic radiosurgery technologies allow the progressive ablation of a brain region with limited adverse effects in surrounding normal tissues. This could be of high interest for the study of the modified behavioral functions in relation with the degree of impairment of the brain structures. Using hypofractionated stereotactic radiotherapy combined with synchrotron microbeam radiation, we investigated, during one year after irradiation, the effects of unilateral radio-ablation of the right Cd on the behavior of Yucatan minipigs. The right Cd was irradiated to a minimal dose of 35.5 Gy delivered in three fractions. MRI-based morphological brain integrity and behavioral functions, i.e. locomotion, motivation/hedonism were assessed. We detected a progressive radionecrosis leading to a quasi-total ablation one year after irradiation, with an additional alteration of surrounding areas. Transitory changes in the motivation/hedonism were firstly detected, then on locomotion, suggesting the influence of different compensatory mechanisms depending on the functions related to Cd and possibly some surrounding areas. We concluded that early behavioral changes related to eating functions are relevant markers for the early detection of ongoing lesions occurring in Cd-related neurological disorders.