After brain surgery, a man began seeing his cat’s eyes in human faces

Karl, a 28-year-old man in the northeastern United States, wakes up and looks at his grey tabby, Luna. For the rest of that day, the people he meets can come out with Luna’s almond-shaped eye sockets, enlarged pupils and stripes. Dartmouth researchers report that the effect began two years ago, after surgery removed part of his right temporal lobe.

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The case, published in the journal Cortex, belongs to a rare family of face-perception disorders in which a face looks wrong even though the eyes and the camera agree it is ordinary. Karl’s version is stranger still, because the distortion borrows from whatever he saw first.

The surgery behind Karl’s symptoms

According to the Dartmouth release distributed through EurekAlert, part of Karl’s right temporal lobe had to be removed to treat an arteriovenous malformation, a tangle of blood vessels connecting arteries and veins that can cause a brain bleed if left alone. The right temporal lobe plays a key role in face processing, so a deficit there is plausible, and Karl’s condition is prosopometamorphopsia, or PMO, in which faces appear distorted.

The release does not say whether his symptoms have faded. The research team plans to keep working with him.

Palinopsia: when the last thing seen lingers

PMO alone would not explain the cat. The second ingredient is palinopsia, in which an earlier-seen image persists or reappears in later perception. Karl sees features of Luna, including the eye shape, the large pupils and the stripes, on people he encounters that day, whether in person or online. If the first thing he looks at in the morning is a person rather than his cat, the pattern flips: he sees that person’s pupils and eye shape on other faces and even on Luna’s face.

The paper’s name makes the direction of travel explicit. It describes human-to-cat and cat-to-human transfer of facial features, and it adds a nod to history by counting the years since the last such report. Brad Duchaine, the lead author, is a professor and chair of psychological and brain sciences at Dartmouth and principal investigator of its Social Perception Lab. He is joined by Antonio Mello Guarini, a doctoral student in that department, and Jennifer Nosker, a neuropsychologist at Brigham and Women’s Hospital.

Forty years after a poodle on a bus

The Cortex paper looks back to a 1986 study in the same journal. That earlier patient was a woman who, nine months after a stroke, saw a poodle on a passenger’s lap and then saw the poodle’s face on every passenger on her bus. Duchaine’s team set Karl’s story beside it as a modern counterpart: in both, a single vivid face gets attached to many others.

Duchaine said the case shows that individual features can be pulled from memory and influence ongoing perception. In other words, the brain does not always treat each face as a fresh image. Pieces of a recent, salient one can leak into the next.

AI-assisted pictures and what PMO usually looks like

Because the experience is internal, the authors needed a way to show it. Duchaine fed a line-drawn sketch into a large language model to make it more photorealistic, and he and Karl then revised the images together for the report. He said such tools can help researchers and patients convey what distorted perception looks like, a task that words alone handle poorly.

Most PMO looks different from Karl’s. The faceblind.org PMO information page, which Duchaine co-founded, describes features that droop, swell, shrink, shift out of place or stretch, and says roughly 75 case reports have been published. Most cases last days or weeks, though some persist for years. Duchaine’s lab has also heard from more than 250 people with face distortions, and some of them were told they had a psychiatric problem and given antipsychotics even though the difficulty was visual.

The scientific literature on the disorder is thin and old, which is part of why single cases carry weight. A review indexed on PubMed, A century of prosopometamorphopsia studies, gathers the published reports across more than a hundred years, and its existence shows how long clinicians have been recording faces that melt, slide or stretch. What Karl adds is a clear link between a specific recent visual experience and the specific feature that migrates, which is difficult to document when patients describe distortions only in the abstract. Duchaine’s group, which calls for more volunteers with PMO on its research page, hopes studies of such cases will improve understanding of PMO and of typical face processing, and may eventually suggest ways to reduce or eliminate the distortions.

An earlier Dartmouth case shows how varied the condition is. ScienceAlert’s 2024 account described a 58-year-old man whose real faces looked demonic while photographs of the same faces looked normal, a pattern linked to a 1-centimeter lesion near the hippocampus.

The full report sits on ScienceDirect under the identifier S0010945226002649 and was published on Oct. 26. Whether Karl’s cat-eyed faces will ever settle down is still an open question that Duchaine’s team says it will keep investigating alongside him.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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