Dogs (Canis lupus familiaris) are susceptible to the Kanizsa’s triangle illusion

Abstract

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.

Visual continuum in non-human animals: serial dependence revealed in dogs

“…Several low-level characteristics of dog vision have been studied; for example size [27–29] and shape perception [30], motion detection [31–33], perception of biological motion [34–37] and global/local processing [38,39]. The findings highlight perceptual similarities between humans and dogs, such as the existence of a global bias in the processing of hierarchical stimuli [38] or the susceptibility to some visual illusions [40,41]. Furthermore, a topic that is relatively well studied in dogs is visual perception and the estimation of quantity [40,42–50].…”

“…The aim of this proof-of-concept study was to assess whether serial dependence also extends to other species besides humans. We chose pet dogs as a model organism, owing to their similarities to humans in terms of visual perception [38][39][40][41], as well as the extensive literature on their cognitive abilities [26] and their availability and trainability in a laboratory environment. Moreover, we opted to assess serial dependence in the domain of quantity discrimination, considering that this ability is well studied in dogs.…”