What if all of the sudden, the right side of people’s faces on your TV appeared to be melting? What if the right side of your own face seemed like it was melting in the mirror? That is the surprising case of a 59-year-old Portuguese man. A study about him was recently published in the scientific journal Current Biology.
The international study was carried out by researchers from the Faculty of Psychology and Educational Sciences of the University of Coimbra, in collaboration with the Hospital of the University Center of Coimbra, Dartmouth College, and the Massachusetts Institute of Technology.
The man, referred to by the fictitious name Augusto in the published study, has an extremely rare neuropsychological condition called hemi-prosopometamorphopsia — only 25 cases are known worldwide. Augusto is unable to visualize faces in a normal way, something that causes him unimaginable suffering.
“This condition is usually characterized by the perception of a distortion in the eyes, nose and/or mouth only on one side of the face. These features seem to be falling off, almost as if they were melting. Nothing more than images of faces causes these distortions,” says Jorge Almeida, the study’s principal investigator and director of the Proaction Lab.
A series of studies with this patient showed for the first time the existence of a step in the processing of faces in which these are rotated and resized to match a pattern. “In the process of recognizing a face we are seeing, we compare that face with those we have in our memory. Thus, whenever we see a face, our brain creates a representation of it and aligns it with a model we have in memory,” adds the researcher. This is, in fact, the way digital face recognition used by Facebook and Google platforms works.
In addition, with this study it was possible to demonstrate that these representations of faces are present in the two hemispheres of the brain and that the representations of the right and left halves of the faces are dissociable. Thus, this study not only increased knowledge about the functioning of the brain, but also supported with scientific evidence one of the most widely used facial recognition methodologies today.
Like many other patients with hemi-prosopometamorphopsia, distortions experienced by Augusto were caused by a lesion in white matter beams that connect the neuronal areas dedicated to faces present in the left and right cerebral hemispheres, preventing the flow of information between them.
One of the experiments carried out with Augusto was the presentation of images from different perspectives (left profile, front and right profile). Augusto indicated that the eyes, mouth and/or nose of the presented faces appeared to be drooping — red areas in the image below. No other deformations were reported when any other non-face images were presented (cars, houses, etc.)
In a second experiment, the researchers presented images of faces in very different forms: the left and right halves of the faces separately, on both sides of the visual field (right and left) and rotated at 90, 180 and 270 degrees.
Regardless of how the faces were presented, Augusto continued to report that the distortions affected the same parts of the face. Even when the face was inverted (mouth up
and eyes down), the patient saw the distortions on the left side. It was still the right eye that seemed to be “melting”, even though in the inverted face it is located on the left side.
“When presenting faces at various angles of rotation, we found that only the right characteristics of the face were distorted, even when the face was presented inverted 180 degrees and those parts of the face were on the left side. The only way to explain this result is that when we process faces, we rotate them and create a model centered on the face and not the observer. In this way, the right eye in this face-centered model is always represented as the right eye, even if it is in our left visual field as when we see an inverted face. This model centered on the face is then compared with an existing model”, concludes Almeida.
The study, “Face-Specific Perceptual Distortions Reveal A View- and Orientation-Independent Face Template“, was authored by Jorge Almeida, Andreia Freixo, Miguel Tábuas-Pereira, Sarah B. Herald, Daniela Valério, Guilherme Schu, Diana Duro, Gil Cunha, Qasim Bukhari, Brad Duchaine, and Isabel Santana.
