Karl, a 28-year-old man living in the northeastern United States, has a grey tabby cat named "Luna". In the morning, his cat is often the first face that he sees.
And on some days from that point on, Karl sees features of his cat—such as the almond-shaped eye sockets, enlarged pupils, and stripes—on the human faces that he encounters that day whether it be in person or online.
Alternatively, if Karl sees a human face at the start of his day, and not his cat, he may see that person's pupils and eye shape in other people's faces and even in his cat's face that day.
Karl has a form of palinopsia, in which something seen earlier persists or reappears in later perception. In Karl's case, his palinopsia leads to face distortions, a condition called prosopometamorphopsia, or PMO.
Karl's experiences are documented in a report in the journal Cortex .
Karl's recurrent palinopsia began two years ago after part of his right temporal lobe had to be removed due to an arteriovenous malformation, tangled blood vessels between arteries and veins, which can lead to a brain bleed if left untreated. The right temporal lobe plays a critical role in face processing.
"This case of Karl seeing his cat's features in human faces and vice versa demonstrates that individual features can be pulled from memory and influence our ongoing perception," says lead author Brad Duchaine , a professor and chair of psychological and brain sciences and principal investigator of the Social Perception Lab at Dartmouth.
In learning about Karl's experience, Duchaine was reminded of a 1986 study published in Cortex reporting on a woman riding a bus who saw a poodle on a passenger's lap and then saw the poodle's face on every passenger on the bus. The woman had experienced a stroke nine months before. However, for Karl, only components of faces are transferred rather than an entire face.
In an effort to illustrate visually what Karl was experiencing, Duchaine prepared a line-drawn sketch that he then fed into a large language model to make the image more photo realistic. He then shared the image with Karl, and the two went back and forth modifying a set of images that are included in the report.
"AI provides researchers like us with the ability to generate more accurate visualizations of what people are experiencing when they're having distorted visual perceptions," says Duchaine. " If you know what the person is experiencing, you can much better research what they're dealing with and try to figure out ways to control it. And now the patient can also take part in that process of creating those visualizations."
"The use of AI is also helpful for patients who want to convey not just to their healthcare professionals, but to their friends and family, what faces look like to them."
The research team plans to work further with Karl in the future.
Duchaine's lab studies PMO and has heard from more than 250 people who experience face distortions. Duchaine says that his lab has heard from people who have been told that they had a psychiatric problem and in some cases, have even been put on antipsychotics, when they are in fact just having visual problems. More information about face processing distortions can be found on Duchaine's PMO website .
Antônio Mello, Guarini, a PhD student in the Department of Psychological and Brain Sciences, and Jennifer Nosker, a neuropsychologist at Brigham and Women's Hospital, also contributed to the study.
