As Far as Eye See: Vergence-Pupil Coupling in Near-Far Depth Switching

TL;DR

This study examines how pupil size fluctuations influence vergence-based depth perception estimates in eye-tracking, revealing variability across individuals and conditions, and demonstrating that controlled lighting can mitigate but not eliminate this effect.

Contribution

It provides empirical evidence that pupil size artefacts affect vergence estimates during real-world depth viewing and explores methods to reduce this influence.

Findings

Pupil-vergence coupling varies across individuals and conditions.

Luminance modulation reduces variability in vergence estimates.

Pupil size fluctuations influence vergence estimates even without visual depth cues.

Abstract

Vergence is widely used as a proxy for depth perception and spatial attention in immersive and real-world eye-tracking studies. In this paper, we investigate how pupil size artefacts affect vergence estimates during real physical depth viewing with a head-mounted eye tracker. Using a beamsplitter setup with physically near and far targets, we elicited controlled convergent and divergent eye movements under static, luminance-modulated, and blockwise fixation conditions. Near and far targets were reliably separable in vergence angle across participants. However, pupil-vergence coupling varied substantially across individuals and conditions. Static illumination produced large inter-participant variability, while luminance modulation reduced this spread, yielding more clustered estimates. Blockwise and audio-cued recordings further showed that pupil-vergence coupling persists even without visual depth onsets. These results suggest that pupil size fluctuations can systematically influence vergence estimates, and that controlled viewing conditions can reduce--but not eliminate--this effect.