The pupillary response of people with aphantasy did not differ significantly between imagined dark and bright objects.

The reaction of the pupils can be used to diagnose aphantasy, a condition that prevents the patient from creating images in his mind, even though they are perceived through the senses. A study led by researchers at UNSW Sydney and published in ‘eLife’ found that the pupils of people with aphantasy did not respond when asked to imagine dark and light objects, while people without aphantasy did.

To first measure the pupillary reflex of people without aphantasy, the researchers recruited 42 study participants, who had visual imagination, and fitted them with glasses to track their eye movements and pupil size.

Participants were then exposed to bright or dark shapes on a gray background, which, as expected, caused pupillary constriction in response to bright shapes (comparable to looking at a bright sky) and pupillary dilation in response to light. dark shapes (after turning off a light).

Next, to test the mind’s ability to visualize objects, participants were asked to simply imagine those same light or dark shapes (with their eyes open, so their pupils would be tracked) and then report on the intensity of those shapes. images.

The researchers found that even in response to imagined bright and dark shapes, participants’ pupils still constricted and dilated appropriately, a pupillary response that was greater in those who reported greater image vividness.

“The pupillary reflex is an adaptation that optimizes the amount of light that reaches the retina,” explains Professor Joel Pearson, lead author of the paper. “And while it was already known that imaged objects can evoke so-called ‘endogenous’ changes in pupil size, we were surprised to see more dramatic changes in those that report more vivid images. This is really the first biological and objective proof of the vividness of the images.”

Finally, having established the link between visual imagery and pupillary response, the researchers wanted to test the effect in 18 individuals with aphantasy. By exposing participants to bright and dark shapes, the researchers found that people with aphantasy showed the same pupillary response as the general population: constriction for bright, dilation for dark.

However, during the second part of the study, in which participants were asked to visualize those same shapes, the pupillary response of people with aphantasy did not differ significantly between imagined dark and bright objects.

“Our results show an exciting new objective method for measuring visual images and the first physiological evidence for aphantasy. With more than 1.3 million Australians believed to have aphantasia, and a further 400 million internationally, we are now close to an objective physiological test, such as a blood test, to see if someone really does have it.” Professor Pearson.

“Our pupils are known to get bigger when we do a more difficult task,” says Lachlan Kay, PhD candidate at the Future Minds Lab, UNSW. “Imagining four objects simultaneously is more difficult than imagining just one. The pupils of those with aphantasy 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 afantasy were actually trying to imagine in this experiment, just not in a visual way.”

Now Professor Pearson and his team at the Future Minds Lab plan to investigate how this new method could be scaled up and applied online to enable global, efficient and objective measurement of images and afantasy.

“We know that thinking or not thinking about pictures affects the amount of detail in lifetime memories, how excited we get when reading, and how well we hold things in short-term memory. This new method will allow us to understand the brain mechanisms of intense images and the global implications of how we think, make decisions and feel, “says Professor Pearson.