Why do animals differ in their susceptibility to geometrical illusions?

Abstract

In humans, geometrical illusions are thought to reflect mechanisms that are usually helpful for seeing the world in a predictable manner. These mechanisms deceive us given the right set of circumstances, correcting visual input where a correction is not necessary. Investigations of non-human animals' susceptibility to geometrical illusions have yielded contradictory results, suggesting that the underlying mechanisms with which animals see the world may differ across species. In this review, we first collate studies showing that different species are susceptible to specific illusions in the same or reverse direction as humans. Based on a careful assessment of these findings, we then propose several ecological and anatomical factors that may affect how a species perceives illusory stimuli. We also consider the usefulness of this information for determining whether sight in different species might be more similar to human sight, being influenced by contextual information, or to how machines process and transmit information as programmed. Future testing in animals could provide new theoretical insights by focusing on establishing dissociations between stimuli that may or may not alter perception in a particular species. This information could improve our understanding of the mechanisms behind illusions, but also provide insight into how sight is subjectively experienced by different animals, and the degree to which vision is innate versus acquired, which is difficult to examine in humans.

Illusion susceptibility in domestic dogs

“…Consistent with other two-choice discrimination studies (including those presented above by Byosiere and colleagues), some subjects were trained to select the longer line, and others were trained to select the shorter line. Substantial controls were required when evaluating the Müller-Lyer illusion, just as the Ebbinghaus-Titchener illusion, as it can be difficult to differentiate if a subject is susceptible to the illusion or simply making a selection based on the overall figure size (Feng et al, 2017). Therefore, Keep et al (2018) conducted multiple experiments to evaluate this possible confound.…”

“…are not limited to 1) using the dog's primary sensory modality, scent, in addition to using vision; 2) evaluating a dog's ability to discriminate between visual stimuli as a preliminary control, using subject behaviour and not simply software (e.g. DogVision as presented in Pongrácz et al, 2017), before conducting complex assessments that (Feng et al, 2017). It is important that future research into illusion susceptibility begin this process, to construct optimal and inclusive theories for comparative illusion susceptibility.…”

“…Within this framework, species that demonstrate human-like susceptibility are primarily classified as global processors, while species that show null or reversed susceptibility are classified as local processors (Kelley & Kelley, 2014). The existence of these perceptual styles likely stems from differences in evolutionary pressures as susceptibility can be advantageous for survival, mating and food competition (Feng et al, 2017;Kelley & Kelley, 2014). For example, Great Bowerbird males create mating illusions, in which females are presented with a TA B L E 1 Depiction, description and theoretical explanations (explaining human susceptibility) of the illusions discussed in this article…”

What do dogs (Canis familiaris) see? A review of vision in dogs and implications for cognition research

“…Part 3: Morphological variation and its effects on eye structure and visual perception Neurobiological investigation suggests there are similarities in visual systems across vertebrates (Lamb, Collin, & Pugh, 2007) as well as in the neural circuitry underlying vision in humans, non-human primates, and other mammals (Masland & Martin, 2007). However, it is also clear that evolutionary pressures have led to differences in perceptual processes (Feng et al, 2016;Lamb et al, 2007). This is largely due to the fact that different species have different physiological features and functions, likely specialized to be adaptive for a given environment.…”

How Illusory Is the Solitaire Illusion? Assessing the Degree of Misperception of Numerosity in Adult Humans

“…Perception of motion illusions have been reported too, with rhesus monkeys (Agrillo et al, 2015a) and guppies and zebrafish (Gori et al, 2014) showing a human-like perception of the Rotating Snake illusion. These studies suggest perceptual systems may be more shared among vertebrates than previously thought (e.g., Nieder, 2002; Kelley and Kelley, 2014), even though no firm conclusion can be taken at this stage as several illusory phenomena have not been studied in species other than humans, and other illusory stimuli produce different outcomes across species in terms of who sees those illusions (for a review, see Feng et al, 2016). …”