August 2023
Volume 23, Issue 9
Open Access
Vision Sciences Society Annual Meeting Abstract  |   August 2023
Mouth-specific distortions: Evidence from prosopometamorphopsia for independent representations of individual facial features
Author Affiliations
  • Alexis Kidder
    Dartmouth College
  • Brad Duchaine
    Dartmouth College
Journal of Vision August 2023, Vol.23, 5006. doi:
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      Alexis Kidder, Brad Duchaine; Mouth-specific distortions: Evidence from prosopometamorphopsia for independent representations of individual facial features. Journal of Vision 2023;23(9):5006.

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      © ARVO (1962-2015); The Authors (2016-present)

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Face perception research has largely emphasized holistic processing of faces (Tanaka & Simonyi, 2016), and work exploring whether and how individual facial features are represented has been limited. However, recent psychophysical, neuroimaging, and single-unit studies suggest individual facial features may be encoded independently (de Haas et al., 2016; Zhang et al., 2021; Waidmann et al., 2022). Here, we present evidence for mouth-specific representations in the human face processing system from a case study of Willie, a right-handed, 38-year-old man who experiences prosopometamorphopsia (PMO). Willie’s day-to-day distortions occur exclusively to mouths, and include whole mouth duplications, illusory mouth motion, and changes to lip shape. We ran a battery of 41 tasks to characterize Willie’s distortions. Of the evoked distortions, 98.7% (157 out of 159) of the distortions were to faces, 94.3% of these distortions were to single features (148 total), and 86% of these distortions only affected mouths (135 total). We tested predictions of four alternative accounts of the process that is producing the distortions: (1) low-level visual processing, (2) general visual object processing, (3) the lower half of viewer-centered face representations, or (4) face-centered mouth-specific representations. To test accounts 1 and 2, Willie viewed 360 simple shapes and 586 common objects and scenes, and reported only two distortions evoked by objects. To evaluate accounts 3 and 4, faces were displayed at different picture-plane orientations. Willie saw distortions to mouths at all six different orientations and did not see distortions to features in the lower half of the face other than mouths. Taken together, these results indicate that Willie’s distortions reflect disruptions to feature-specific, face-centered representations. His case indicates mouths are encoded independently from other face features and suggests that other facial features may also be represented independently.


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