Aphantasia Could Be Diagnosed Based on Pupil Size

Pupil size fluctuates to let just the right amount of light into the eye. Vision is improved by contracting the brightness and dilating in the dark. New research shows that beyond light changes, pupil size might also change based on perceptual and cognitive circumstances.

Mental imagery was shown to facilitate pupillary responses to light in this study published in the Association for Psychological Science (APS).

Another study, published in the Journal of Vision (JoV), suggests the pupil constricts in response to a high-light luminance object in a photo, such as the sun.

A condition known as aphantasia is diagnosed as the inability to produce mental images in the mind. Aphantasia can stem from birth or manifest later in life, despite being otherwise healthy. Researchers studied pupillary responses of people who experience aphantasia to better understand how the brain’s visual and ocular reflexes work.

The study, published in eLife, compared the pupillary responses of people with and without aphantasia.

Professor Julia Simner leads the MULTISENSE lab at the University of Sussex and was not involved in the study. After analyzing the data, she said, “The fascinating finding reported here is that people imagining light or dark objects show the same type of pupillary action as we would normally find when the eyes are exposed to light and dark objects in the real world. This suggests that their imagination is treated [as] a simulation of the real world. [Meanwhile,] people with aphantasia — who imagine in a more abstract way because they cannot build a picture in their mind’s eye — don’t show the same effect.”

The study participants were asked to imagine 32 white or gray shapes while their pupil size was measured. Other experiments were conducted, as well as a questionnaire. Researchers concluded that people without aphantasia reacted to perceived and imagined luminous images, which affected their pupillary size. Those with aphantasia did not note a change in pupillary size when perceiving or imagining luminous images.


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