Visual discrimination of size and perception of the Delboeuf illusion in the domestic cat (Felis silvestris catus): A developmental disjunction?

Abstract

To date, no studies have examined the ontogeny of susceptibility to visual illusions in nonhuman mammals. Our previous study on the perception of the Delboeuf illusion by adult cats suggested they perceive this illusion, and that the visual processing involved in size judgment differs in the presence or absence of a misleading surround. We therefore asked whether weanling kittens are susceptible to the Delboeuf visual illusion, as adult cats are. Like the adults, kittens were presented with a series of 2-way food choice tasks where same-or different-size food portions were presented on same-or different-size plates. In control trials, the kittens significantly discriminated between 2 different amounts of food on same-size plates and, like adults, they chose the larger amount; when the difference between the food amounts was greater, the kittens chose the larger amount more reliably. Olfactory control trials confirmed that kittens, like adults, used visual cues when comparing quantities in this setting. In contrast to adults, however, in the illusion trials with same-size food portions on different-size plates, the kittens did not choose either of the 2 different-size plates significantly above chance and so did not appear to perceive the illusion. This suggests heterochronicity in the development of the cat visual system in which the ability to discriminate sizes develops before susceptibility to an illusion using these stimuli. Remaining questions include at what age susceptibility to visual illusions emerges and whether this depends on continued maturation of the brain, on experience of the visual world, or both.

Are you as fooled as I am? Visual illusions in human (Homo) and nonhuman (Sapajus, Gorilla, Pan, Pongo) primate species.

“…Finally, given the observed developmental patterns in human subjects it seems essential to investigated potential age effects also in nonhuman subjects. Some studies suggest developmental effects in mammals (Bánszegi et al, 2021) and birds (Rosa Salva et al, 2013) but unfortunately, the size of the current nonhuman primate sample does not allow for any meaningful analysis of this kind. Larger samples through multilab collaborations (ManyPrimates, 2019) and counterbalanced age compositions of the testing groups would allow for more controlled analyses of age effects in nonhuman subjects in the future.…”

“…Besides primates, other mammalian species have been shown to be susceptible to geometric illusions too—for example, in cats (Bánszegi et al, 2021; Szenczi et al, 2019), dogs (Byosiere et al, 2020; Keep et al, 2018), and horses (Cappellato et al, 2020).…”

Optical illusions in different ungulates species

“…In our study, we tested the susceptibility of subjects belonging to 4 different ungulate species (i.e., guanacos, llamas, Skudde sheep and Damara goats) to the Müller-Lyer and Delboeuf illusions. Following the procedures previously used with other species (Bánszegi et al, 2021;Cappellato et al, 2020) we found that the study subjects perceived both the Müller-Lyer and the Delboeuf illusions in a similar way to humans, with no signi cant differences across species.…”

Perception of optical illusions in ungulates: insights from goats, sheep, guanacos and llamas

“…Comparisons with wild ungulates will thus be interesting to test the possible effect of environmental conditions on ungulate susceptibility to optical illusions. Similarly, future studies would benefit from the inclusion of a developmental approach, as susceptibility to illusions might change through age also in species other than humans (see e.g., Bánszegi et al 2021 , in cats). Finally, due to time constraints, we also did not include a control condition that is typically used when testing the Delboeuf illusion (Parrish and Beran 2014 ), in which the smaller food is on the smaller plate and the larger food on the larger plate, which allows excluding the possibility that subjects’ choices depend on the food-to-plate ratio.…”