Focal Length Affects Depicted Shape and Perception of Facial Images

PLoS One. 2016 Feb 19;11(2):e0149313. doi: 10.1371/journal.pone.0149313. eCollection 2016.

Abstract

Static photographs are currently the most often employed stimuli in research on social perception. The method of photograph acquisition might affect the depicted subject's facial appearance and thus also the impression of such stimuli. An important factor influencing the resulting photograph is focal length, as different focal lengths produce various levels of image distortion. Here we tested whether different focal lengths (50, 85, 105 mm) affect depicted shape and perception of female and male faces. We collected three portrait photographs of 45 (22 females, 23 males) participants under standardized conditions and camera setting varying only in the focal length. Subsequently, the three photographs from each individual were shown on screen in a randomized order using a 3-alternative forced-choice paradigm. The images were judged for attractiveness, dominance, and femininity/masculinity by 369 raters (193 females, 176 males). Facial width-to-height ratio (fWHR) was measured from each photograph and overall facial shape was analysed employing geometric morphometric methods (GMM). Our results showed that photographs taken with 50 mm focal length were rated as significantly less feminine/masculine, attractive, and dominant compared to the images taken with longer focal lengths. Further, shorter focal lengths produced faces with smaller fWHR. Subsequent GMM revealed focal length significantly affected overall facial shape of the photographed subjects. Thus methodology of photograph acquisition, focal length in this case, can significantly affect results of studies using photographic stimuli perhaps due to different levels of perspective distortion that influence shapes and proportions of morphological traits.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Face / anatomy & histology*
  • Female
  • Femininity
  • Humans
  • Male
  • Masculinity
  • Optics and Photonics*
  • Photography*
  • Visual Perception*

Grants and funding

JF was supported by Charles University Grant Agency GAUK 918214 (http://www.cuni.cz/ukeng-33.html), VT and KK by Czech Science Foundation GAČR P407/15-05048S (http://gacr.cz/en/) and VT, JF, and JH by the project "National Institute of Mental Health (NIMH-CZ)", grant number ED2.1.00/03.0078 (and the European Regional Development Fund, http://ec.europa.eu/regional_policy/en/funding/erdf/). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.