Methodological Challenges in the Assessment of Dogs' (Canis lupus familiaris) Susceptibility of the Ebbinghaus-Titchener Illusion Using the Spontaneous Choice Task

Abstract

Visual illusions represent an innovative method to investigate animal visual perception. One well known geometric illusion is the Ebbinghaus-Titchener illusion, which consists of two identically sized target circles with one surrounded by large inducer circles and the other surrounded by small inducer circles. Humans are susceptible to this illusion, underestimating the size of the target circle surrounded by larger inducers and overestimating the size of the target circle surrounded by smaller inducers. In the present study, we investigated whether pet dogs (Canis lupus familiaris) perceive the Ebbinghaus-Titchener illusion in a spontaneous choice task by adapting and replicating the methodology of Miletto Petrazzini et al. (2017). Twenty-five pet dogs were presented with two stimuli in which a food reward was embedded. Each subject participated in 18 total trials, 12 size discrimination control trials (where one food reward was larger than the other) and six illusion trials (where identically sized food rewards were presented). Dogs, as a group, failed to demonstrate a significant preference for the larger food reward in control trials, and demonstrated null susceptibility, performing at chance, in the illusion trials. The chance performance on controls prevents further interpretation regarding canine illusion susceptibility; however, it invokes a discussion regarding the methodological challenges associated with conducting spontaneous-choice tasks. In an attempt to provide guidance for future research, we provide a review of canine illusion susceptibility to the Ebbinghaus-Titchener illusion and detailed recommendations to help mitigate extraneous factors to help further research of animal illusion susceptibility.

Response to geometrical visual illusions in non-human animals: a meta-analysis

“…Realistically, selecting a testing method freely may not always be possible, as spontaneous testing might not be suitable for all species (e.g. [ 57 ] where it was suggested that spontaneous choice test may invoke an inhibitory control problem in dogs). Finally, both methodologies have the issue of evaluating visual acuity.…”

Seeing Things: A Community Science Investigation into Motion Illusion Susceptibility in Domestic Cats (Felis silvestris catus) and Dogs (Canis lupus familiaris)

“…While it is possible that susceptibility was not observed, such contradictory results could be methodological in nature. Despite the spontaneous choice paradigm’s effectiveness in revealing illusory susceptibility via subjects’ attraction to perceived motion without the (potentially confounding) use of food, it is also known for its flaws [ 8 , 26 ]. Specifically, subjects may orient more to the illusion due to other factors (e.g., context of food reward) rather than perceived motion.…”