An extremely rare condition caused a man to suffer from a bizarre and highly distressing symptom that makes faces appear half melted. The case study, published in the journal Current Biology, describes how the patient is unable to see faces without them being visually distorted despite his sight being otherwise normal.
Known as hemi-prosopometamorphopsia – or hemi-PMO if you can’t quite manage that mouthful – the condition has only ever been recorded 25 times in medical history and is caused by some form of brain damage. For the patient in this case study, nicknamed A.D by the researchers, the condition came as the result of a lesion in the splenium region of his brain, an area associated with sight. He had first presented to clinicians five years ago complaining that all faces appeared to melt on one side, creating an image that significantly diminished his quality of life. Hemi-PMO has rarely been studied as it often fades with time.
To better understand the strange illness, the researchers showed A.D a series of images of faces and other objects on different planes, at different angles and different perspectives. The results showed that he was capable of correctly seeing inanimate objects, but faces were almost always distorted despite being rotated and turned. The faces appeared as melted to A.D in the red regions shown on the photo below, indicating that his visual system viewed the upside-down face with the same template as used to understand the upright face.
The crux of the condition is said to be comparable to facial recognition technology, which uses a library of images of faces to fill in the gaps when looking at a new face. It’s thought that when we see a face for the first time, we incorporate all historic examples of faces seen to create an image in our mind. It was a fault in the area of the brain responsible for this in A.D’s brain that led to him viewing faces a bit like a Salvador Dali painting.
“Every time we see a face, the brain adjusts our representation of that face so its size, viewpoint, and orientation is matched to faces stored in memory, just like computer face recognition systems such as those used by Facebook and Google,” said co-author Brad Duchaine, a professor of psychological and brain sciences and the principal investigator of the Social Perception Lab at Dartmouth College. “By aligning the perceived face with faces stored in memory, it’s much easier for us to determine whether the face is one we’ve seen before.”
Hemi-PMO is one of a number of disorders that disrupt facial recognition. Another called prosopagnosia, also known as face blindness, prevents people from ever recognizing the same face twice causing significant disruption to their social and quality of life.