  Recently, extended reality (XR) displays including augmented reality (AR) and
virtual reality (VR) have integrated eye tracking capabilities, which could
enable novel ways of interacting with XR content. The vergence angle of the
eyes constantly changes according to the distance of fixated objects. Here we
measured vergence angle for eye fixations on real and simulated target objects
in three different environments: real objects in the real-world (real), virtual
objects in the real-world (AR), and virtual objects in the virtual world (VR)
using gaze data from an eye-tracking device. In a repeated-measures design with
13 participants, Gaze-measured Vergence Angle (GVA) was measured while
participants fixated on targets at varying distances. As expected, results
showed a significant main effect of target depth such that increasing GVA was
associated with closer targets. However, there were consistent individual
differences in baseline GVA. When these individual differences were controlled
for, there was a small but statistically-significant main effect of environment
(real, AR, VR). Importantly, GVA was stable with respect to the starting depth
of previously fixated targets and invariant to directionality (convergence vs.
divergence). In addition, GVA proved to be a more veridical depth estimate than
subjective depth judgements.
