As Far as Eye See: Vergence-Pupil Coupling in Near-Far Depth Switching
This work addresses measurement accuracy issues for researchers using eye-tracking in immersive and real-world studies, though it is incremental in refining existing methods.
The study investigated how pupil size artifacts affect vergence angle estimates during depth perception using a head-mounted eye tracker, finding that pupil-vergence coupling varies across individuals and conditions, with controlled conditions reducing but not eliminating the effect.
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.