Dog eye movements are slower than human eye movements

Perception of animate motion in dogs

Various motion cues can lead to the perception of animacy, including (1) simple motion characteristics such as starting to move from rest, (2) motion patterns of interactions like chasing, or (3) the motion of point-lights representing the joints of a moving biological agent. Due to the relevance of dogs in comparative research and considering the large variability within the species, studying animacy perception in dogs can provide unique information about how selection for specific traits and individual-level (social) differences may shape social perception. Despite these advantages, only a few studies have investigated the phenomenon in dogs. In this mini-review, we discuss the current findings about how specific motion dynamics associated with animacy drive dogs' visual attention.

Do dogs preferentially encode the identity of the target object or the location of others' actions?

The ability to make sense of and predict others' actions is foundational for many socio-cognitive abilities. Dogs (Canis familiaris) constitute interesting comparative models for the study of action perception due to their marked sensitivity to human actions. We tested companion dogs (N = 21) in two screen-based eye-tracking experiments, adopting a task previously used with human infants and apes, to assess which aspects of an agent's action dogs consider relevant to the agent's underlying intentions. An agent was shown repeatedly acting upon the same one of two objects, positioned in the same location. We then presented the objects in swapped locations and the agent approached the objects centrally (Experiment 1) or the old object in the new location or the new object in the old location (Experiment 2). Dogs' anticipatory fixations and looking times did not reflect an expectation that agents should have continued approaching the same object nor the same location as witnessed during the brief familiarization phase; this contrasts with some findings with infants and apes, but aligns with findings in younger infants before they have sufficient motor experience with the observed action. However, dogs' pupil dilation and latency to make an anticipatory fixation suggested that, if anything, dogs expected the agents to keep approaching the same location rather than the same object, and their looking times showed sensitivity to the animacy of the agents. We conclude that dogs, lacking motor experience with the observed actions of grasping or kicking performed by a human or inanimate agent, might interpret such actions as directed toward a specific location rather than a specific object. Future research will need to further probe the suitability of anticipatory looking as measure of dogs' socio-cognitive abilities given differences between the visual systems of dogs and primates.

Dogs Rely On Visual Cues Rather Than On Effector-Specific Movement Representations to Predict Human Action Targets

The ability to predict others' actions is one of the main pillars of social cognition. We investigated the processes underlying this ability by pitting motor representations of the observed movements against visual familiarity. In two pre-registered eye-tracking experiments, we measured the gaze arrival times of 16 dogs (Canis familiaris) who observed videos of a human or a conspecific executing the same goal-directed actions. On the first trial, when the human agent performed human-typical movements outside dogs' specific motor repertoire, dogs' gaze arrived at the target object anticipatorily (i.e., before the human touched the target object). When the agent was a conspecific, dogs' gaze arrived to the target object reactively (i.e., upon or after touch). When the human agent performed unusual movements more closely related to the dogs' motor possibilities (e.g., crawling instead of walking), dogs' gaze arrival times were intermediate between the other two conditions. In a replication experiment, with slightly different stimuli, dogs' looks to the target object were neither significantly predictive nor reactive, irrespective of the agent. However, when including looks at the target object that were not preceded by looks to the agents, on average dogs looked anticipatorily and sooner at the human agent's action target than at the conspecific's. Looking times and pupil size analyses suggest that the dogs' attention was captured more by the dog agent. These results suggest that visual familiarity with the observed action and saliency of the agent had a stronger influence on the dogs' looking behaviour than effector-specific movement representations in anticipating action targets.

How to improve data quality in dog eye tracking

Pupil-corneal reflection (P-CR) eye tracking has gained a prominent role in studying dog visual cognition, despite methodological challenges that often lead to lower-quality data than when recording from humans. In the current study, we investigated if and how the morphology of dogs might interfere with tracking of P-CR systems, and to what extent such interference, possibly in combination with dog-unique eye-movement characteristics, may undermine data quality and affect eye-movement classification when processed through algorithms. For this aim, we have conducted an eye-tracking experiment with dogs and humans, and investigated incidences of tracking interference, compared how they blinked, and examined how differential quality of dog and human data affected the detection and classification of eye-movement events. Our results show that the morphology of dogs' face and eye can interfere with tracking methods of the systems, and dogs blink less often but their blinks are longer. Importantly, the lower quality of dog data lead to larger differences in how two different event detection algorithms classified fixations, indicating that the results of key dependent variables are more susceptible to choice of algorithm in dog than human data. Further, two measures of the Nyström & Holmqvist (Behavior Research Methods, 42(4), 188-204, 2010) algorithm showed that dog fixations are less stable and dog data have more trials with extreme levels of noise. Our findings call for analyses better adjusted to the characteristics of dog eye-tracking data, and our recommendations help future dog eye-tracking studies acquire quality data to enable robust comparisons of visual cognition between dogs and humans.

Eye tracking: empirical foundations for a minimal reporting guideline

In this paper, we present a review of how the various aspects of any study using an eye tracker (such as the instrument, methodology, environment, participant, etc.) affect the quality of the recorded eye-tracking data and the obtained eye-movement and gaze measures. We take this review to represent the empirical foundation for reporting guidelines of any study involving an eye tracker. We compare this empirical foundation to five existing reporting guidelines and to a database of 207 published eye-tracking studies. We find that reporting guidelines vary substantially and do not match with actual reporting practices. We end by deriving a minimal, flexible reporting guideline based on empirical research (Section "An empirically based minimal reporting guideline").

Oculomotor Abnormalities in a Sheep (Ovis aries) Model of Huntington's Disease: Towards a Biomarker for Assessing Therapeutic Efficacy

BACKGROUND

Huntington's disease (HD) is characterized by a loss of control of motor function that causes the presence of abnormal eye movements at early stages.

OBJECTIVE

To determine if, compared to normal sheep, HD sheep have abnormal eye movements.

METHODS

We measured eye movements in a transgenic sheep (Ovis aries) model of HD using a purpose-built, head-mounted sheep oculometer. This allows us to measure saccades without the need for either behavioral training or head fixation. At the age of testing (6 years old), the HD sheep were pre-manifest. We used 21 sheep (11 HD, 10 normal).

RESULTS

We found small but significant differences in eye movements between normal (control) and HD sheep during vestibular ocular reflex (VOR)- and vestibular post-rotational nystagmus (PRN)-based tests.

CONCLUSIONS

Two measures were identified that could distinguish normal from HD sheep; the number of PRN oscillations when tested in the dark and the gain (eye movement to head movement ratio) during the VOR when tested in the light. To our knowledge, this is the first study in which eye movements have been quantified in sheep. It demonstrates the feasibility of measuring and quantifying human-relevant eye movements in this species. The HD-relevant deficits show that even in 'premanifest' sheep there are measurable signs of neurological dysfunction that are characterized by loss of control of eye movements.

Eye Tracking in Dogs: Achievements and Challenges

In this article, we review eye-tracking studies with dogs (Canis familiaris) with a threefold goal; we highlight the achievements in the field of canine perception and cognition using eye tracking, then discuss the challenges that arise in the application of a technology that has been developed in human psychophysics, and finally propose new avenues in dog eye-tracking research. For the first goal, we present studies that investigated dogs' perception of humans, mainly faces, but also hands, gaze, emotions, communicative signals, goal-directed movements, and social interactions, as well as the perception of animations representing possible and impossible physical processes and animacy cues. We then discuss the present challenges of eye tracking with dogs, like doubtful picture-object equivalence, extensive training, small sample sizes, difficult calibration, and artificial stimuli and settings. We suggest possible improvements and solutions for these problems in order to achieve better stimulus and data quality. Finally, we propose the use of dynamic stimuli, pupillometry, arrival time analyses, mobile eye tracking, and combinations with behavioral and neuroimaging methods to further advance canine research and open up new scientific fields in this highly dynamic branch of comparative cognition.

Exploring the advantages of using artificial agents to investigate animacy perception in cats and dogs

Self-propelled motion cues elicit the perception of inanimate objects as animate. Studies usually rely on the looking behaviour of subjects towards stimuli displayed on a screen, but utilizing artificial unidentified moving objects (UMOs) provides a more natural, interactive context. Here, we investigated whether cats and dogs discriminate between UMOs showing animate vs inanimate motion, and how they react to the UMOs' interactive behaviour. Subjects first observed, in turn, the motion of an animate and an inanimate UMO, and then they could move freely for 2 min while both UMOs were present (two-way choice phase). In the following specific motion phase, the animate UMO showed one of three interactive behaviours: pushing a ball, a luring motion, or moving towards the subject (between-subject design). Then, subjects could move freely for 2 min again while the UMO was motionless. At the end, subjects were free to move in the room while the UMO was moving semi-randomly in the room. We found that dogs approached and touched the UMO(s) sooner and more frequently than cats, regardless of the context. In the two-way choice phase, dogs looked at the animate UMO more often, and both species touched the animate UMO more frequently. However, whether the UMO showed playing, luring or assertive behaviour did not influence subjects' behaviour. In summary, both species displayed distinctive behaviour towards the animate UMO, but in dogs, in addition to the physical contact this was also reflected by the looking behaviour. Overall, dogs were more keen to explore and interact with the UMO than cats, which might be due to the general increased stress of cats in novel environments. The findings indicate the importance of measuring multiple behaviours when assessing responses to animacy. The live demonstration using artificial agents provides a unique opportunity to study social perception in nonhuman species.

Chasing perception in domestic cats and dogs

Chasing motion is often used to study the perception of inanimate objects as animate. When chasing interaction and independent motions between two agents are displayed simultaneously on a screen, we expect observers to quickly perceive and recognise the chasing pattern (because of its familiarity) and turn their attention to the independent motion (novelty effect). In case of isosceles triangles as moving figures, dogs and humans both display this behaviour, but dogs initially preferred to look at the chasing pattern whereas humans started to increase their gaze towards the independent motion earlier. Here, we compared whether family cats perceive moving inanimate objects as animate and whether their looking behaviour is similar to that of small family dogs. We displayed a chasing and independent motion side by side on a screen in two consecutive trials and assessed subjects’ looking behaviour towards the motions. Similarly to previous studies, we found that dogs eventually looked longer at the independent motion, but cats preferred to look at the independent motion at the beginning of the video display and only later shifted their attention to the chasing motion. No difference was found in the frequency of gaze alternation of the two species. Thus, although cats discriminate between the chasing and independent motions, it is not clear whether this discrimination is controlled by animate motion cues. The difference may originate from their ecological situation and/or may be explained by specific perceptual mechanisms.

Selection for specific behavioural traits does not influence preference of chasing motion and visual strategy in dogs

Perception of inanimate objects as animate based on motion cues alone seems to be present in phylogenetically distant species, from birth (humans and chicks). However, we do not know whether the species’ social and ecological environment has an influence on this phenomenon. Dogs serve as a unique species to investigate whether selection for specific behavioural traits influences animacy perception. We tested purebred companion dogs, and assigned them into two groups based on the type of work they were originally selected for: (1) Chasers, tracking and chasing prey; (2) Retrievers, mark and remember downed game. We displayed isosceles triangles presenting a chasing pattern vs moving independently, in parallel on a screen. We hypothesised that Chasers prefer to look at chasing and Retrievers eventually focus their visual attention on the independent motion. Overall, we did not find a significant difference between groups regarding the looking duration of dogs or the frequency of their gaze alternation between the chasing and independent motions. Thus it seems that selection for specific traits does not influence the perception of animate entities within the species.