Abstract
Facial symmetry is believed to have an evolutionary significance and so its detection should be robust in natural settings. Previous studies of facial symmetry detection have used front views of faces where the decision could be made on 2D image properties rather than 3D facial properties. These studies also employed comparative judgements, which could be influenced by attractiveness rather than symmetry. Two experiments explored the ability to detect typical levels of 3D facial asymmetry (contrasted with wholly symmetrical faces) from 2D projections of faces. Experiment 1 showed that asymmetry detection was impaired by inversion but even more impaired by 90 degrees rotation demonstrating the importance of the vertical reflection. Asymmetry detection was also reduced by yaw rotation of the head but still above-chance at 30 degrees rotation. Experiment 2 explored the effect of asymmetrical lighting and yaw rotation up to 45 degrees. Detection of asymmetry was affected by asymmetrical lighting and yaw rotation in a non-additive manner. The results are discussed in terms of the special role that faces and vertical symmetry play in visual perception.
Highlights
Human faces, like many biological forms, show high levels of mirror symmetry
The angle of yaw significantly interacted with lighting, The results show that people are able to assess facial symmetry even when the face is not presented frontally and with asymmetrical lighting
The current research provides a range of insights into the perception of facial symmetry
Summary
Like many biological forms, show high levels of mirror symmetry. The human body is asymmetrical with many internal organs showing directional asymmetry developed in the first few weeks of life [1,2]. Even facial symmetry is not perfect and faces tend to display varying levels of fluctuating asymmetry [3]. It has been proposed that lower levels of fluctuating asymmetry are reflective of an individual’s greater health and genetic quality [4,5]. It is argued that lower fluctuating asymmetry is a consequence of greater development stability [6]. Higher levels of facial symmetry should, be more attractive in mates as they communicate greater genetic fitness. We should be good at detecting asymmetries as they are evolutionarily significant in the same way as food sources or threats
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