Windows to the Soul: Pupils Reveal ‘Aphantasia’ – The Absence of Visual Imagination

"Exposing participants to bright and dark shapes, the researchers found that aphantasic individuals exhibited the same pupillary response as the general population: constriction to bright, dilation to dark.

However, during the study’s second component where participants were asked to visualise those same shapes, the pupillary response of aphantasic individuals did not significantly differ in response to imagined dark versus imagined bright objects.

“One of the problems with many existing methods to measure imagery is that they are subjective, that is to say they rely on people being able to accurately assess their own imagery. Our results show an exciting new objective method to measure visual imagery,” says Prof Pearson, “and the first physiological evidence of aphantasia. With over 1.3 million Australians thought to have aphantasia, and 400 million more internationally, we are now close to an objective physiological test, like a blood test, to see if someone truly has it.”

To ensure the aphantasic participants were really attempting imagery, the researchers included a further experimental condition, requesting aphantasic individuals to visualise four shapes, instead of one.

While the pupils of those with aphantasia showed no difference when imagining light versus dark objects, they did show a difference imagining one versus four objects, suggesting more mental effort, thereby negating an explanation of non-participation by aphantasic individuals."