Higher-level mechanisms detect facial symmetry

Abstract

The role of symmetry detection in early visual processing and the sensitivity of biological visual systems to symmetry across a wide range of organisms suggest that symmetry can be detected by low-level visual mechanisms. However, computational and functional considerations suggest that higher-level mechanisms may also play a role in facial symmetry detection. We tested this hypothesis by examining whether symmetry detection is better for faces than comparable patterns, which share low-level properties with faces. Symmetry detection was better for upright faces than for inverted faces (experiment 1) and contrastreversed faces (experiment 2), implicating high-level mechanisms in facial symmetry detection. In addition, facial symmetry detection was sensitive to spatial scale, unlike low-level symmetry detection mechanisms (experiment 3), and showed greater sensitivity to a 458 deviation from vertical than is found for other aspects of face perception (experiment 4). These results implicate specialized, higher-level mechanisms in the detection of facial symmetry. This specialization may reflect perceptual learning resulting from extensive experience detecting symmetry in faces or evolutionary selection pressures associated with the important role of facial symmetry in mate choice and 'mind-reading' or both.

Behind the Looking-Glass: A Review on Human Symmetry Perception

“…In fact, these seems to be the case for faces. Symmetry detection is better in normal faces than in inverted (turned upside-down) and contrast-reversed faces [95]. Moreover, if faces are tilted away from vertical in steps of 45°, detectability decreases monotonically from 0°to 135°.…”

Factors Affecting the Perception of 3D Facial Symmetry from 2D Projections

“…This is important because Little and Jones [17] presented evidence that inversion did not affect the process of asymmetry detection. Further, Rhodes and colleagues' [14] evidence of an inversion effect could have been a result of symmetry preference being used instead of symmetry detection. The current research shows a clear inversion effect in symmetry detection.…”

“…Typically, pairs of almost identical faces are presented in which one face has more asymmetry than the other. The participant chooses which face is either more symmetrical [14], more attractive [15,16] or both [17,18]. In the attractiveness task, an attractiveness preference for more symmetrical faces is therefore interpreted from increased selection of the most symmetrical of the pair: the more common the selection of the symmetrical faces the stronger the preference for symmetry over asymmetry.…”

“…Rhodes and colleagues [14] used a consecutively presented 2afc design to show that symmetry could be detected in both upright and inverted faces at above-chance levels. The symmetry was detected significantly less accurately for inverted faces than for upright faces.…”

Robot Assisted Smile Recovery

“…Studies have shown that angular deviations are more significant to the detection of facial symmetry than linear displacements (Rhodes et al;. The angle of displacement of both grid-line and muscle markers was analyzed and compared to the displacement during a natural smile.…”