The effects of visual degradation on face discrimination

Daphne L. Mcculloch*, Gunter Loffler, Kirsty Colquhoun, Natalie Bruce, Gordon N. Dutton, Michael Bach

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

23 Citations (Scopus)

Abstract

Purpose: People with reduced visual acuity (VA) and/or contrast sensitivity have difficulty recognizing faces and facial expressions. We have quantified these difficulties, using a synthetic face discrimination task employing both normal and artificially degraded vision.

Methods: VA and contrast thresholds were measured using an optimised staircase procedure [Freiburg acuity Test (FrACT)] in 25 young adults (aged 18-24years) with corrected visual acuity of 0.0 logMAR or better and with four levels of vision degraded with Bangerter occlusion foils. For face discrimination, male face images were synthesised from 37 cardinal points (position of eyes, width of nose, head shape etc) derived from frontal face photographs and manipulated by altering the points as a fraction of the mean head radius. Face discrimination thresholds (% difference) were measured from a simultaneous four-alternative forced choice of 'odd one out' from three identical faces and one that differed. Psychometric functions were measured for four participants with normal and degraded vision. Subsequently, the difference between faces was fixed at twice the discrimination thresholds and the size of the faces manipulated using the FrACT threshold procedure in 25 participants. Data were converted to equivalent face discrimination distances for realistic face dimensions.

Results: With normal vision, face discrimination thresholds ranged from 2.7% to 5.6%; these increased systematically and were more variable with visual degradation. When manipulating face size, face discrimination distance was highly correlated with both acuity and contrast sensitivity (r2=0.77 and 0.80 respectively, p<0.01). The mean distance with normal vision was 15.3m (14.5-16.2±S.E.M.). With vision degraded to 0.6 logMAR (6/24 Snellen, contrast threshold 15%) the mean face discrimination distance was reduced to 3.9m (3.7-4.1, ±S.E.M.).

Conclusions: Poor face discrimination has a profound impact on real-life social communication. Here we report that artificial visual degradation also adversely impacts a synthetic face recognition task. As a rule of thumb, reduction in VA of 0.3 logMAR (halving the decimal VA) reduces the face recognition distance by a factor of 0.6 times. The FrACT-based face discrimination task provides an efficient new tool to quantify and monitor face discrimination ability.

Original languageEnglish
Pages (from-to)240-248
Number of pages9
JournalOphthalmic and Physiological Optics
Volume31
Issue number3
Early online date17 May 2011
DOIs
Publication statusPublished - May 2011

Keywords

  • face discrimination
  • Freiburg Acuity Test
  • low vision
  • synthetic faces

ASJC Scopus subject areas

  • Ophthalmology
  • Optometry
  • Sensory Systems

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