Pupil Size Reflects Trial‐Level Variability in Imagery Vividness During Immersive Storytelling but Not (or Hardly) Individual Differences in Trait Imagery
Vanbuckhave, C., Eikner, J. S., Laeng, B., Onnis, L., & Mathôt, S. (2026). Pupil size reflects trial‐level variability in imagery vividness during immersive storytelling but not (or hardly) individual differences in trait imagery. Psychophysiology, 63(4). doi:10.1111/psyp.70298
Abstract
Previous research has shown that the eyes' pupils are larger when imagining dark as compared to bright objects or scenes. On the basis of this, it has been claimed that pupil size is a sensitive marker of mental imagery vividness. We investigated this claim in three experiments, conducted in two countries (Norway and The Netherlands; N total = 115), in which participants read, listened, or freely imagined stories that evoked a sense of darkness or brightness. In addition, self‐reports of vividness were collected for each story to measure variations in imagery vividness during the experiment; and through questionnaires (VVIQ, SUIS), to measure differences in task‐unrelated imagery abilities at the individual level. We found that the effect of larger pupils for darkness‐evoking stories than brightness‐evoking stories was highly variable. Importantly, we found that this pupil‐size difference (dark–bright) was consistently largest for vividly imagined stories. Finally, we did not find any convincing relationship between this pupil‐size difference and individual differences in questionnaire‐based imagery. We conclude that the strength of pupil‐size changes in response to imagined darkness or brightness better reflects trial‐by‐trial fluctuations in imagery vividness within an individual than individual differences in imagery vividness as a personal trait.
What This Study Is About
Researchers wanted to know if our eyes can "see" what we are imagining. They tested whether our pupils (the black circles in our eyes) change size when we think about bright or dark scenes, and if this could be used as an objective test to measure how vivid someone’s mental imagery—the ability to picture things in your mind—really is.
How They Studied It
The team worked with 115 participants across three different experiments. Participants either read or listened to short stories—some describing bright, sunny environments and others describing dark, shadowy places. While they were immersed in the stories, a high-tech eye-tracker measured their pupil size. Afterward, everyone rated how life-like their mental pictures were and completed a standard questionnaire to see if they had aphantasia (the inability to see any images in the "mind's eye").
What They Found
The researchers found that our bodies actually react to our thoughts! Just like a camera lens adjusting to light, participants' pupils grew larger when imagining dark scenes and smaller when imagining bright ones.
However, there was a twist: this "pupil reflex" was great at showing when a person was having a particularly vivid moment, but it wasn't very good at comparing different people. For example, someone who generally has very strong imagery didn't necessarily have a stronger pupil reaction than someone with average imagery. The test was better at tracking a single person's "ups and downs" in focus rather than acting as a "vividness thermometer" for everyone.
What This Might Mean
This suggests that while our pupils are connected to our imagination, using them to "prove" if someone has aphantasia is tricky. It suggests that the pupillary response is a sensitive tool for measuring moment-to-moment effort, but it might not be a permanent "signature" of how someone's brain is wired. Because the changes in pupil size were very tiny and varied a lot between people, we should be careful not to claim this is a perfect "lie detector" for the mind's eye yet.
One Interesting Detail
The researchers found that the pupil effect was much stronger when people listened to audio stories (like a podcast) compared to when they read text on a screen! This suggests that listening might allow the brain to focus more on "painting" the mental picture.