Fixed-bias versus state-dependent pupil–vergence coupling under physically grounded viewing

Determine whether pupil–vergence coupling measured by infrared video-based eye trackers during physically grounded near–far depth viewing can be modeled as a single fixed, correctable bias that remains consistent across viewing distances, or whether the coupling varies with the physical viewing state.

Background

Video-based eye trackers infer gaze direction from image features such as the pupil center, making estimates sensitive to pupil size changes. Prior studies have shown pupil-size artifacts can bias gaze and vergence measurements, and physiological coordination among vergence, accommodation, and pupil size (the near triad) may further complicate measurement.

Most existing work either minimizes pupil dynamics, treats pupil size as a luminance/cognitive signal, or examines disparity-driven rather than physically grounded depth changes. As a result, it remains unresolved whether pupil–vergence coupling behaves like a fixed, correctable bias that could be handled with a universal calibration, or whether it changes with viewing state in real near–far viewing conditions.