Truth is in the eye of the beholder: Perception of the Müller-Lyer illusion in dogs.

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.

Animals can assign novel odours to a known category.

The ability to identify a novel stimulus as a member of a known category allows an organism to respond appropriately towards it. Categorisation is thus a fundamental component of cognition and an essential tool for processing and responding to unknown stimuli. Therefore, one might expect to observe it throughout the animal kingdom and across sensory domains. There is much evidence of visual categorisation in non-human animals, but we currently know little about this process in other modalities. In this experiment, we investigated categorisation in the olfactory domain. Dogs were trained to discriminate between 40 odours; the presence or absence of accelerants formed the categorical rule. Those in the experimental group were rewarded for responding to substrates with accelerants (either burnt or un-burnt) and inhibit responses to the same substrates (either burnt or un-burnt) without accelerants (S+ counterbalanced). The pseudocategory control group was trained on the same stimuli without the categorical rule. The experimental group learned the discrimination and animals were able to generalise to novel stimuli from the same category. None of the control animals were able to learn the discrimination within the maximum number of trials. This study provides the first evidence that non-human animals can learn to categorise non-biologically relevant odour information.

Short term consequences of preventing visitor access to kennels on noise and the behaviour and physiology of dogs housed in a rescue shelter.

Re-homing centres present a range of potential stressors to kennelled dogs which are likely to impact negatively on their welfare. Despite the presence of visitors to the kennel often being considered a potential stressor, empirical investigation into their impact on the behaviour and welfare of kennelled dogs in re-homing centres is lacking. This study investigated the influence of changing visitor access policy from open access to prohibited viewing at kennels (with organised single meetings for viewing dogs outside of the kennel environment) on the welfare of 15 dogs housed in a dog-only re-homing facility. Data were collected across a number of domains comprising kennel noise levels, behavioural measures (activity, repetitive behaviour, response to human approach); physiological measures (urinary cortisol:creatinine ratios); sickness events and faecal scoring. The general kennel noise levels were significantly lower when visitor access to the kennel area was restricted. Furthermore, dogs were found to display behaviour indicative of improved welfare during this time period; dogs spent significantly more time sedentary, less time moving and exhibited significantly fewer episodes of repetitive behaviours. No significant change was seen in the urinary cortisol:creatinine ratio, nor in sickness behaviour, faecal scoring or response to a human approach test. Overall, the results from this study suggest that restricting visitors from viewing the dogs while in their kennels may be better for the dogs' short term welfare.