Does shading on great argus Argusianus argus feathers create a three-dimensional illusion?

Many animals use shading to infer the three-dimensional (3D) shape of objects, and mimicking natural shading patterns can produce the illusion of 3D form on a flat surface. Over 150 years ago, Charles Darwin noted that the ocelli (eyespots) on the feathers of the great argus , when held vertically d...

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Bibliographic Details
Published in:	Biology letters (2005) Vol. 18; no. 11; p. 20220393
Main Authors:	Firkins, James M E, Kelley, Laura A
Format:	Journal Article
Language:	English
Published:	England The Royal Society 09-11-2022
Subjects:	Animal Behaviour Animals Chickens Depth Perception Feathers Female Form Perception Humans Illusions Male shape from shading pictorial relief illusion
Online Access:	Get full text
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Summary:	Many animals use shading to infer the three-dimensional (3D) shape of objects, and mimicking natural shading patterns can produce the illusion of 3D form on a flat surface. Over 150 years ago, Charles Darwin noted that the ocelli (eyespots) on the feathers of the great argus , when held vertically during courtship displays to females, were perfectly shaded to resemble 3D hemispheres to human viewers. We tested whether these ocelli appear 3D to birds by training chickens to select images of either convex or concave shapes using shading cues, and then presenting them with images of great argus ocelli. Chickens successfully learned how to discriminate between convex and concave shapes, and treated the great argus pheasant ocelli in the same way as convex training stimuli. Our findings are consistent with previous studies that birds can perceive 3D shape from shading cues in a similar manner to humans. The perception of great argus ocelli as consistent with 3D shape by avian viewers suggests that shape illusions can play a role in male courtship.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 Electronic supplementary material is available online at https://doi.org/10.6084/m9.figshare.c.6268923.
ISSN:	1744-957X 1744-9561 1744-957X
DOI:	10.1098/rsbl.2022.0393