A simple test can reveal whether someone unknowingly lives with a hidden disability known as aphantasia – a condition that leaves people unable to form mental images in their mind.
Often undiagnosed and poorly understood, aphantasia affects the brain’s ability to visualise pictures, scenes or faces, even though eyesight itself is completely normal.
Although estimates suggest between two and five per cent of people have aphantasia, the vast majority are never formally diagnosed.
Because the condition is invisible and not routinely tested for, experts believe millions are unaware they have it and only discover it later in life by chance.
People with the condition cannot picture a loved one’s face, imagine a sunset, or visualise an object when their eyes are closed – something most people assume everyone can do.
Because it does not affect intelligence, language or outward functioning, aphantasia is largely invisible and many people only realise they have it in adulthood, after discovering that others experience vivid mental imagery that they do not.
Now, Australian researchers say they have developed the first objective biological test to identify the condition.
Scientists at the University of New South Wales found aphantasia can be detected by monitoring pupillary response – the way the pupils expand and contract in response to light – according to findings published in 2022 in the journal eLife.
A simple test could reveal if you have a little-known condition that sees people unable to visualise imagery in their mind
The researchers monitored pupil size in participants with and without aphantasia while they were shown bright and dark shapes against a grey background.
Both groups – 42 people without aphantasia and 18 who reported having it – showed a normal pupil response when actually viewing the images, demonstrating that their eyes and visual pathways were functioning normally.
However, when both groups were then asked to visualise the same light and dark shapes in their mind, a clear difference emerged.
Participants without aphantasia showed the expected pupil response, with their pupils changing size depending on whether they were imagining light or dark objects.
By contrast, the pupils of those with aphantasia did not change at all when they attempted to visualise the images.
‘Our results show an exciting new objective method to measure visual imagery, and the first physiological evidence of aphantasia,’ said senior author Dr Joel Pearson, a neuroscientist, in a blog published by the university.
He described it as the first test of its kind for the condition.
‘This really is the first biological, objective test for imagery vividness,’ Dr Pearson said.
Crucially, the findings also counter the idea that people with aphantasia are simply not trying to imagine images.
Although their pupils did not respond to imagined brightness or darkness, they did dilate when participants were asked to imagine four objects rather than one – a sign of increased mental effort.
‘Our pupils are known to get larger when we are doing a more difficult task,’ said Lachlan Kay, a PhD candidate in the Future Minds Lab at the university.
‘Imagining four objects simultaneously is more difficult than imagining just one.
‘The pupils of those with aphantasia dilated when they imagined four shapes compared to one but did not change based on whether the shapes were bright or dark.
‘This indicated that the participants with aphantasia were indeed trying to imagine in this experiment, just not in a visual way.’
Professor Pearson described the finding as ‘very exciting’, saying it was the first time researchers had shown that people with aphantasia actively attempt mental imagery.
He said it ‘puts to rest claims that they may simply not be attempting to create a mental image’.
It is estimated that around two to five per cent of the population have aphantasia – equivalent to millions of people worldwide – according to the British Psychological Society.
Rather than thinking in pictures, people with the condition tend to process information through facts, concepts and abstract knowledge, says the Aphantasia Network, a global online community for those affected.
The term comes from ancient Greece, where the philosopher Aristotle described ‘phantasia’ as the mind’s ability to form images.
There is no single presentation of the condition. Some people are born with it – known as congenital aphantasia – while others acquire it later in life due to brain injury, trauma or medical conditions.
Aphantasia can also be complete or partial. Some people experience no mental imagery at all, while others report dim, fleeting or fragmented images.
While visual aphantasia is the most common form, researchers say the condition can also affect the ability to imagine sounds, touch, smells, tastes and movement.
