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

• Published in: Animal Cognition
• Main Authors: Lõoke, Miina, Marinelli, Lieta, Guérineau, Cécile, Agrillo, Christian, Mongillo, Paolo
• Other Authors: Fondazione Cassa di Risparmio di Padova e Rovigo, Department of Comparative Biomedicine and Food Science, University of Padua, Università degli Studi di Padova
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer Science and Business Media LLC 2021
• Subjects: Experimental and Cognitive Psychology; Ecology, Evolution, Behavior and Systematics; Canis lupus
• Online Access: http://dx.doi.org/10.1007/s10071-021-01533-0; https://link.springer.com/content/pdf/10.1007/s10071-021-01533-0.pdf; https://link.springer.com/article/10.1007/s10071-021-01533-0/fulltext.html

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.