Dynamic Corridor Illusion in Pigeons: Humanlike Pictorial Cue Precedence Over Motion Parallax Cue in Size Perception.

Yuya Hataji,Hika Kuroshima,Kazuo Fujita

doi:10.1177/2041669520911408

Abstract

Depth information is necessary for perceiving the real size of objects at varying visual distances. To investigate to what extent this size constancy present in another vertebrate class, we addressed the two questions using pigeons: (a) whether pigeons see a corridor illusion based on size constancy and (b) whether pigeons prioritize pictorial cues over motion parallax cues for size constancy, like humans. We trained pigeons to classify target sizes on a corridor. In addition, we presented a dynamic version of corridor illusion in which the target and corridor moved side by side. Target speed was changed to manipulate motion parallax. With the static corridor, pigeons overestimated the target size when it was located higher, indicating that pigeons see a corridor illusion like humans. With the dynamic corridor, the pigeons overestimated the target size depending on target position, as in the static condition, but target speed did not affect their responses, indicating that the pictorial precedence also applies to pigeons. In a follow-up experiment using the same stimulus, we confirmed that humans perceive object size based on pictorial cues. These results suggest that size constancy characteristics are highly similar between pigeons and humans, despite the differences in their phylogeny and neural systems.

Highlights

Depth information is necessary for perceiving the real size of objects at varying visual distances
Perceived sizes in PNMF and PNMN were significantly above the physical sizes—PNMF, 1.049: 0.041, t(5) 1⁄4 2.946, p 1⁄4 .032, d 1⁄4 1.203; PNMN, 1.096: 0.033, t(5) 1⁄4 7.038, p 1⁄4 .001, d 1⁄4 2.873. These results suggest that size constancy in humans depends more on pictorial cues than motion parallax cues, as found in previous studies (Gregory, 1970; Luo et al, 2007; Wade & Hughes, 1999; Watt & Bradshaw, 2003)
Neither the effect of species nor the interaction with other factors was significant—species, F(1, 10) 1⁄4 1.578, p 1⁄4 .238, bstd 1⁄4 0.063; Species Â Pictorial, F(1, 10) 1⁄4 0.822, p 1⁄4 .386, bstd 1⁄4 0.037; Species Â Motion, F(1, 10) 1⁄4 1.649, p 1⁄4 .228, bstd 1⁄4 0.323; Species Â Pictorial Â Motion, F(1, 10) 1⁄4 1.823, p 1⁄4 .207, bstd 1⁄4 0.253. These findings indicate that the extent to which pictorial and motion parallax cues contribute to size constancy is not different between pigeons and humans

Summary

Introduction

Depth information is necessary for perceiving the real size of objects at varying visual distances. They found that the chimpanzees chose the farther one on a corridor background when two objects of identical size were presented and that the accuracy declined when the smaller object was presented on a farther point and the perceived difference in size of two objects diminished These studies suggest that size constancy using pictorial cues is shared at least in the order primates. Learning improved as the cues were additively combined, indicating that pigeons use all pictorial depth cues for the ordering discrimination From these studies, it is hypothesized that birds resemble primates in being sensitive to the corridor illusion. One goal in the present study was to investigate whether pigeons perceive the corridor illusion, known to occur in baboons and chimpanzees

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