Do domestic dogs (Canis lupus familiaris) perceive the Delboeuf illusion?

Abstract

In the last decade, visual illusions have been repeatedly used as a tool to compare visual perception among species. Several studies have investigated whether non-human primates perceive visual illusions in a human-like fashion, but little attention has been paid to other mammals, and sensitivity to visual illusions has been never investigated in the dog. Here, we studied whether domestic dogs perceive the Delboeuf illusion. In human and non-human primates, this illusion creates a misperception of item size as a function of its surrounding context. To examine this effect in dogs, we adapted the spontaneous preference paradigm recently used with chimpanzees. Subjects were presented with two plates containing food. In control trials, two different amounts of food were presented in two identical plates. In this circumstance, dogs were expected to select the larger amount. In test trials, equal food portion sizes were presented in two plates differing in size: if dogs perceived the illusion as primates do, they were expected to select the amount of food presented in the smaller plate. Dogs significantly discriminated the two alternatives in control trials, whereas their performance did not differ from chance in test trials with the illusory pattern. The fact that dogs do not seem to be susceptible to the Delboeuf illusion suggests a potential discontinuity in the perceptual biases affecting size judgments between primates and dogs.

Do Dogs Demonstrate Susceptibility to a Vertically Presented Ponzo Illusion?

“…Although it has been previously proposed that terrestrial animals may consistently share the same perceptual experiences of geometrical illusions as humans , the results from this study and others in domestic dogs Miletto Petrazzini et al, 2017) suggest this may not be the case. In a previous study assessing susceptibility to the Ebbinghaus-Titchener illusion, reversed susceptibility was found in this same group of dogs when presented with two different illusory contexts , and two studies have failed to observe canine susceptibility to the Delboeuf illusion Miletto Petrazzini et al, 2017).…”

“…In a previous study assessing susceptibility to the Ebbinghaus-Titchener illusion, reversed susceptibility was found in this same group of dogs when presented with two different illusory contexts , and two studies have failed to observe canine susceptibility to the Delboeuf illusion Miletto Petrazzini et al, 2017). Baboons, the only other terrestrial species to have been assessed on the Ebbinghaus-Titchener illusion, failed to demonstrate susceptibility to the illusion (Barbet & Fagot, 2002), and while some terrestrial species, such as chimpanzees, macaques and capuchin monkeys Parrish, Brosnan, & Beran, 2015), have demonstrated human-like susceptibility to the Delboeuf illusion, others, like ring-tailed lemurs, have not (Santacà et al, 2017).…”

“…In contrast, two studies have found that dogs do not demonstrate susceptibility to the Delboeuf illusion Miletto Petrazzini et al, 2017), although, in one of these studies, individual differences were again apparent (Figure 1, image 3). More recently, we assessed whether dogs demonstrate susceptibility to the Ponzo illusion (Figure 1, images 4  6).…”

Do Dogs See the Ponzo illusion?

“…However, we had no a-priori predictions in regards to performance in the illusion condition. While susceptibility to the Ponzo illusion is widespread and has been observed in humans and other mammals (Barbet & Fagot, 2002;Bayne & Davis, 1983;Fujita, 1996Fujita, , 1997Fujita et al, 1991;Imura et al, 2008;Nakagawa, 2002;Timney & Keil, 1996), the fact that dogs have previously demonstrated reversed susceptibility or no susceptibility when presented with other geometric illusions (Byosiere et al, 2016;Miletto Petrazzini et al, 2016) meant that we were unable to predict if dogs would perceive the illusion at all and, if they did, whether this would be in the same or opposite manner to humans.…”

“…Furthermore, while dogs as a group appear not to be susceptible to the Delboeuf illusion, certain individuals may demonstrate susceptibility, also in a reversed direction than humans and other mammals (Byosiere et al, 2016;Miletto Petrazzini, Bisazza, & Agrillo, 2016). Variation in illusion susceptibility is not unique to dogs.…”