Exploring the Müller-Lyer illusion in a nonavian reptile (Pogona vitticeps)

Visual illusions have been widely used to compare visual perception among birds and mammals to assess whether animals interpret and alter visual inputs like humans, or if they detect them with little or no variability. Here, we investigated whether a nonavian reptile (Pogona vitticeps) perceives the Müller-Lyer illusion, an illusion that causes a misperception of the relative length of 2 line segments. We observed the animals' spontaneous tendency to choose the larger food quantity (the longer line). In test trials, animals received the same food quantity presented in a spatial arrangement eliciting the size illusion in humans; control trials presented them with 2 different-sized food portions. Bearded dragons significantly selected the larger food quantity in control trials, confirming that they maximized food intake. Group analysis revealed that in the illusory test trials, they preferentially selected the line length estimated as longer by human observers. Further control trials excluded the possibility that their choice was based on potential spatial bias related to the illusory pattern. Our study suggests that a nonavian reptile species has the capability to be sensitive to the Müller-Lyer illusion, raising the intriguing possibility that the perceptual mechanisms underlying size estimation might be similar across amniotes. (PsycInfo Database Record (c) 2020 APA, all rights reserved).