S114 – Thresholds for Visual Perception of Facial Asymmetry

Abstract

Objectives To determine the degree of facial asymmetry which is required to trigger conscious perception in the observer. Methods A normal face was manipulated typical to facial paralysis changes, using advanced computer program to create progressive images of increasing asymmetry, in one millimeter increments, up to 10 mm. This was performed on 1) brow, 2) oral commissure, and 3) combined brow and oral commissure. The study included both altered and unaltered versions of the model face, in addition to other unaltered images. Images were presented to volunteer observers unaware of the purpose of the study. Results I) Oral commissure asymmetry: the threshold for visual perception was 3 mm by the majority of people (73%) when each image was presented for 10 seconds. When up to 4 mm of mouth angle asymmetry was noticed, it was perceived as “noticeable, but acceptable” by 83%, while 6 mm or greater of asymmetry was perceived as “unacceptable” by 60%. Presenting the images for 2 sec/image (quick look) demonstrated that 53% detected the asymmetry at 5 mm. II) Brow asymmetry: 70% perceived the asymmetry at 3 mm. III) Combined oral commissure and eye brow: 100% of people perceived the oral commissure asymmetry at a lower threshold than the brow asymmetry. Conclusions The pilot data and the discussion will provide insight into the processes of visual perception of facial asymmetry, and guidance for surgeons and patients sorting through their options. Further efforts are under way to pursue these concepts in 3-dimensional, dynamic subjects.