Millions of people may be unknowingly living with a hidden neurological condition that prevents them from seeing images in their mind's eye, known as aphantasia. For the first time, researchers have developed an objective biological test to identify it.
The Pupil Test: A Window to the Mind's Eye
Scientists from the University of New South Wales in Australia have pioneered a simple test that can detect aphantasia by monitoring a person's pupillary response. Published in the journal eLife in 2022, their study found that while viewing actual images, the pupils of people with and without aphantasia reacted normally to light and dark.
However, a stark difference emerged when participants were asked to visualise those same shapes in their imagination. The pupils of those without aphantasia changed size in response to imagined brightness or darkness, but the pupils of those with the condition showed no change. This provides the first physiological evidence for the condition.
Not a Lack of Effort, But a Different Kind of Thinking
A crucial finding from the research counters the assumption that individuals with aphantasia are simply not trying hard enough to visualise. The study involved 42 people without aphantasia and 18 who reported having it.
When asked to imagine four objects at once instead of one, the pupils of those with aphantasia dilated—a clear sign of increased cognitive effort. "This indicated that the participants with aphantasia were indeed trying to imagine in this experiment, just not in a visual way," explained Lachlan Kay, a PhD candidate involved in the study.
Senior author Dr Joel Pearson, a neuroscientist, described this as "very exciting," stating it was the first proof that people with the condition actively attempt mental imagery, putting to rest claims they are not making an effort.
Understanding the 'Hidden' Condition
Aphantasia is an often undiagnosed condition where individuals cannot voluntarily form mental pictures of faces, scenes, or objects. Estimates from the British Psychological Society suggest it affects between two and five per cent of the population, equating to millions of people globally.
People with the condition might be unable to picture a loved one's face or imagine a sunset, though their eyesight is normal. It does not affect intelligence or general functioning, which is why many only discover they have it in adulthood upon realising others experience vivid mental imagery.
The term originates from ancient Greek, where 'phantasia' referred to the mind's ability to create images. Presentations vary: some are born with it (congenital aphantasia), while others acquire it later from brain injury or trauma. It can be complete or partial, and while visual imagery is most commonly affected, it can also involve other senses like sound or smell.
According to the Aphantasia Network, those with the condition tend to process the world through facts, concepts, and abstract knowledge rather than pictures. With this new, objective test, researchers hope to improve understanding and diagnosis of this little-known but fascinating aspect of human cognition.
