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Animals : an open access journal from MDPI2020; 10(9); 1673; doi: 10.3390/ani10091673

Susceptibility to Size Visual Illusions in a Non-Primate Mammal (Equus caballus).

Abstract: The perception of different size illusions is believed to be determined by size-scaling mechanisms that lead individuals to extrapolate inappropriate 3D information from 2D stimuli. The Muller-Lyer illusion represents one of the most investigated size illusions. Studies on non-human primates showed a human-like perception of this illusory pattern. To date, it is not clear whether non-primate mammals experience a similar illusory effect. Here, we investigated whether horses perceive the Muller-Lyer illusion by using their spontaneous preference for the larger portion of carrot. In control trials, we presented horses with two carrot sticks of different sizes, and in test trials, carrot sticks of identical size were shown to the subjects together with arrowheads made of plastic material and arranged in a way meant to elicit the Müller-Lyer illusion in human observers. In control trials, horses significantly discriminated between the smaller and larger carrot stick. When presented with the illusion, they showed a significant preference for the carrot that humans perceive as longer. Further control trials excluded the possibility that their choices were based on the total size of the carrot stick and the arrowheads together. The susceptibility of horses to this illusion indicates that the perceptual mechanisms underlying size estimation in perissodactyla might be similar to those of primates, notwithstanding the considerable evolutionary divergence in the visual systems of these two mammalian groups.
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Publication Date: 2020-09-17 PubMed ID: 32957449PubMed Central: PMC7552233DOI: 10.3390/ani10091673Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

This study explores whether non-primate mammals, specifically horses, are susceptible to visual size illusion, like the Muller-Lyer illusion, similar to human beings and non-human primates. The research found that horses, when given an option to choose from two carrot pieces manipulated to look different in size using typical Muller-Lyer illusion techniques, did choose the one that appeared larger, showing susceptibility to size estimation illusions similar to primates.

Objective and Methodology of the Study

  • The main objective of the study is to understand if horses can perceive visual illusions, specifically the Muller-Lyer illusion.
  • The Muller-Lyer illusion was chosen because it is one of the most investigated size illusions and generates the perception of unequal sizes using the same size elements.
  • To test this perception, horses were presented with two carrots of different sizes (control trial) and two carrots of the same size manipulated with arrow heads to elicit the illusion of different sizes (test trials).
  • The horse’s choice of a carrot in the test trials provided insight into their perception and susceptibility to the visual illusion.

Findings of the Study

  • In control trials, horses significantly discriminated between the smaller and larger carrot stick, indicating their ability to differentiate between different sizes.
  • In the test trials, horses showed a significant preference for the carrot stick which appeared longer due to the Muller-Lyer illusion.
  • Further control trials ruled out the possibility that the horses’ choices were based on the total size of the carrot stick and the attached arrowheads.
  • This confirmed that horses, like humans and non-human primates, are susceptible to the Muller-Lyer illusion.

Implications of the Study

  • The results suggest that the mechanisms underlying size estimation in horses might be similar to those in primates, despite significant evolutionary divergence in their visual systems.
  • This conclusion aids in our wider understanding of mammalian perception and cognition.
  • Moreover, this study opens up possibilities for further research on perceptual abilities in different animal species and how these abilities evolved.

Cite This Article

APA
Cappellato A, Miletto Petrazzini ME, Bisazza A, Dadda M, Agrillo C. (2020). Susceptibility to Size Visual Illusions in a Non-Primate Mammal (Equus caballus). Animals (Basel), 10(9), 1673. https://doi.org/10.3390/ani10091673

Publication

Animals : an open access journal from MDPI
ISSN: 2076-2615
NlmUniqueID: 101635614
Country: Switzerland
Language: English
Volume: 10
Issue: 9
PII: 1673

Researcher Affiliations

Cappellato, Anansi
  • Department of General Psychology, University of Padova, 35131 Padova, Italy.
Miletto Petrazzini, Maria Elena
  • Department of Biomedical Sciences, University of Padova, Via Bassi 58, 35131 Padova, Italy.
Bisazza, Angelo
  • Department of General Psychology, University of Padova, 35131 Padova, Italy.
  • Padua Neuroscience Center, University of Padova, Via Orus 2, 35131 Padova, Italy.
Dadda, Marco
  • Department of General Psychology, University of Padova, 35131 Padova, Italy.
Agrillo, Christian
  • Department of General Psychology, University of Padova, 35131 Padova, Italy.
  • Padua Neuroscience Center, University of Padova, Via Orus 2, 35131 Padova, Italy.

Grant Funding

  • STARS@unipd.it / Universitu00e0 degli Studi di Padova

Conflict of Interest Statement

The authors declare no conflict of interest.

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Citations

This article has been cited 4 times.
  1. Beran MJ, Parrish AE. Consistently Inconsistent Perceptual Illusions in Nonhuman Primates: The Importance of Individual Differences. Animals (Basel) 2022 Dec 21;13(1).
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