If you are experiencing face distortions or similar symptoms, please contact us.
Face processing depends on a complex network of brain regions, and dysfunction within this network can produce a wide variety of face processing impairments. When faces or parts of faces are perceived as distorted, the condition is known as prosopometamorphopsia (PMO). “Prosopo” comes from the Greek word for face prosopon while “metamorphopsia” refers to perceptual distortions.
Not surprisingly, people with PMO often find it disturbing to look at other people’s faces. Fortunately, most cases last only a few days or weeks. Around 30 case reports on people with PMO have been published, so the condition appears to be quite rare.
PMO comes in different forms. The condition causes features to appear distorted in a variety of ways -- they may droop, appear smaller or larger than normal, be out of position, or seem stretched. PMO is typically classified based on the region of the face that is affected by distortion. We currently have little understanding about why people experience different types of PMO, but it is one of the many questions that we are interested in investigating.
In full-face PMO, features on both sides of the face are distorted (Dalrymple et al., 2014; Blom et al., 2014). For example, a woman who we tested in our lab, reported distortions to many face parts (both eyes, nose, mouth, and the contour of the face)(Dalrymple et al., 2014). In addition, the distortions she saw grew larger over time. Below you can see how the patient described her perceived distortions for two faces.
In hemi-prosopometamorphopsia (Hemi-PMO), features on one side of the face are distorted while features on the other side of the face look normal (Grusser et al., 1991, Cho et al., 2011, Almeida et al., 2020). Patient A.D. who we reported on in Almeida et al. (2020) often saw features on the right side of the face as if they were melting, but he did not see distortions on the left side of faces or in any other objects or body parts. When faces were turned upside down, the distortions continued to affect the same features they affected in upright faces. See figure below illustrating how A.D. might have seen the same photo when it was upright and upside down (the distorted part of the faces are shaded red to highlight them). However, in other cases (Nagaishi et al., 2015), the features distorted appear to change when faces are rotated. Considerably more cases of hemi-PMO have been reported in the neurological literature than full-face PMO, so hemi-PMO appears to be the more common type of PMO.
The brain regions we use to process faces are located primarily in our occipital and temporal lobes (back of the brain), and it is likely that abnormalities in these regions or the white matter connections between these regions cause PMO. In some cases, damage appears to be restricted to gray matter. Interestingly though, the cause of the majority of hemi-PMO cases is damage to white matter connections that link regions in the two hemispheres. These connections make up part of the corpus callosum and, in particular, the splenium. Below is an image showing the small splenium lesion that caused the hemi-PMO that Patient A.D. experiences (Almeida et al., 2020).
Perceptual distortions can affect any aspect of our visual experience. In PMO, faces are specifically impacted, but distortions can also have specific effects on other visual categories (e.g., objects, bodies, etc.). If you’re experiencing distortions that affect a particular visual category, we’d be interested in hearing about the distortions you’re seeing.
Little is known about the different types of PMO because few cases have been studied. Our lab is very interested in studying people with PMO. We hope that our research can lead to a deeper understanding of PMO and also how face processing works in typical brains. In addition, this research may help us identify interventions that reduce or eliminate face distortions in PMO.
If you are experiencing PMO or know someone who is, we would love to hear from you.
Professor at Dartmouth College
Department of Psychological and Brain Sciences
Co-Founder of faceblind.org
I’m a professor in the Department of Psychological and Brain Sciences at Dartmouth. Much of our lab’s research is focused on neuropsychological investigations of face processing. If you’re interested in our research, you can learn more here.
To get in touch about PMO or other types of category-specific metamorphopsia, please email me at: firstname.lastname@example.org (or use link below).