Proceedings of the Royal Society B: Biological Sciences
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Symmetry perception by poultry chicks and its implications for three-dimensional object recognition

Elena Mascalzoni

Elena Mascalzoni

Department of General Psychology, University of Padova, Padova, Italy

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,
Daniel Osorio

Daniel Osorio

School of Life Sciences, University of Sussex, Brighton BN1 9QG, UK

[email protected]

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,
Lucia Regolin

Lucia Regolin

Department of General Psychology, University of Padova, Padova, Italy

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and
Giorgio Vallortigara

Giorgio Vallortigara

CIMeC—Center for Mind/Brain Sciences, and Department of Cognitive Sciences, University of Trento, Rovereto, Italy

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Published:https://doi.org/10.1098/rspb.2011.1486

    Bilateral symmetry is visually salient to diverse animals including birds, but whereas experimental studies typically use bilaterally symmetrical two-dimensional patterns that are viewed approximately fronto-parallel; in nature, animals observe three-dimensional objects from all angles. Many animals and plant structures have a plane of bilateral symmetry. Here, we first (experiment I) give evidence that young poultry chicks readily generalize bilateral symmetry as a feature of two-dimensional patterns in fronto-parallel view. We then test the ability of chicks to recognize symmetry in images that would be produced by the transformed view produced by a 40° horizontal combined with a 20° vertical rotation of a pattern on a spherical surface. Experiment II gives evidence that chicks trained to distinguish symmetrical from asymmetrical patterns treat rotated views of symmetrical ‘objects’ as symmetrical. Experiment III gives evidence that chicks trained to discriminate rotated views of symmetrical ‘objects’ from asymmetrical patterns generalize to novel symmetrical objects either in fronto-parallel or rotated view. These findings emphasize the importance of bilateral symmetry for three-dimensional object recognition and raise questions about the underlying mechanisms of symmetry perception.

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