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The pupillary light response as a physiological index of aphantasia, sensory and phenomenological imagery strength

DOI: 10.7554/elife.72484
Kay, L., Keogh, R., Andrillon, T., & Pearson, J. (2022). The pupillary light response as a physiological index of aphantasia, sensory and phenomenological imagery strength. eLife, 11. doi:10.7554/eLife.72484

Abstract

The pupillary light response is an important automatic physiological response which optimizes light reaching the retina. Recent work has shown that the pupil also adjusts in response to illusory brightness and a range of cognitive functions, however, it remains unclear what exactly drives these endogenous changes. Here, we show that the imagery pupillary light response correlates with objective measures of sensory imagery strength. Further, the trial-by-trial phenomenological vividness of visual imagery is tracked by the imagery pupillary light response. We also demonstrated that a group of individuals without visual imagery (aphantasia) do not show any significant evidence of an imagery pupillary light response, however they do show perceptual pupil light responses and pupil dilation with larger cognitive load. Our results provide evidence that the pupillary light response indexes the sensory strength of visual imagery. This work also provides the first physiological validation of aphantasia.

Authors

  • Lachlan Kay2
  • Rebecca Keogh14
  • Thomas Andrillon2
  • Joel Pearson28

Understanding the Pupillary Light Response and Aphantasia

Overview/Introduction

The pupillary light response is a natural reflex that helps regulate the amount of light entering our eyes. Recent studies have shown that this response is not only triggered by actual light but also by our imagination and cognitive activities. This research explores how the pupillary light response is linked to the strength of visual imagery in our minds. It also investigates aphantasia, a condition where individuals lack visual imagery, providing the first physiological evidence of this phenomenon.

Methodology

  • Participants: The study involved 42 participants from the general population and 18 individuals with aphantasia.
  • Tasks: Participants were asked to imagine visual stimuli and their pupillary responses were measured. A binocular rivalry task was also used to assess visual imagery strength.
  • Measurements: Pupillary responses were recorded using eye-tracking technology during tasks involving visual imagery and perception.

Key Findings

  • Imagery and Pupillary Response: In the general population, stronger and more vivid visual imagery was associated with greater changes in pupil size.
  • Aphantasia: Individuals with aphantasia did not show significant pupillary changes during imagery tasks, confirming their lack of visual imagery.
  • Cognitive Load: Despite the lack of imagery, aphantasic individuals showed normal pupil responses to cognitive load, indicating active engagement in tasks.

Implications

  • Understanding Aphantasia: This study provides objective evidence for aphantasia, helping to validate the experiences of those who report an inability to visualize.
  • Applications in Neuroscience: The findings could aid in developing new methods for assessing visual imagery and cognitive functions, potentially benefiting psychological and neurological research.
  • Broader Impact: Understanding the link between imagery and physiological responses could lead to better insights into how the brain processes visual information.

Limitations

  • Sample Size: The study involved a relatively small number of aphantasic participants due to the rarity of the condition.
  • Age Differences: There was an age difference between the general and aphantasic groups, which could influence results, although it was not found to be a significant factor.
In summary, this research highlights the connection between visual imagery and physiological responses, offering new insights into the nature of aphantasia and the broader workings of the human mind.