What is it about?
Humans overestimate the length of a horizontal line when inward arrowheads are located at both ends of the line (>-<) and underestimate the length of the line when outward arrowheads are located (<->). This very famous phenomenon is called the Müller-Lyer illusion. The results of this study suggest that budgerigars also perceive the Müller-Lyer illusion as humans do. Furthermore, interestingly, the magnitude of illusion in budgerigars was larger than that in humans. This implies that, for budgerigars, a line flanked by inward arrowheads (>-<) may look even longer than for humans, while a line flanked by outward arrowheads (<->) may look even shorter than for humans.
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Why is it important?
It is very difficult to investigate how non-human animals perceive illusory figures without linguistic communication. This study used an original experimental method to demonstrate that budgerigars did not simply answer the length of the entire Müller-Lyer figure, but were influenced by arrowheads when answering the length of a line out of the figure. In studying visual illusions in animals, it is very important to examine and discuss the validity of experimental methods and results.
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This page is a summary of: Budgerigars (Melopsittacus undulatus) perceive the Müller-Lyer illusion., Journal of Experimental Psychology Animal Learning and Cognition, April 2022, American Psychological Association (APA), DOI: 10.1037/xan0000321.
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