Varifocal Displays Reduce the Impact of the Vergence-Accommodation Conflict on 3D Pointing Performance in Augmented Reality Systems

TL;DR

The paper addresses VAC-related degradation in AR 3D pointing by testing a custom varifocal AR display in a controlled, ISO-standard pointing task. A two-study, within-subject design compares varifocal and fixed-focal viewing, showing an average performance boost in MT and THP under varifocal conditions, but with substantial inter-individual variability linked to baseline performance. The findings highlight baseline-dependent benefits: participants with poorer fixed-focal performance gain more from varifocal support, while high-baseline users may see smaller or negative effects. Overall, the work demonstrates the potential of varifocal displays to mitigate VAC in interaction tasks, while underscoring the need to account for individual differences in design and evaluation of AR depth interfaces.

Abstract

This paper investigates whether a custom varifocal display can improve 3D pointing performance in augmented reality (AR), where the vergence-accommodation conflict (VAC) is known to impair interaction. Varifocal displays have been hypothesized to alleviate the VAC by dynamically matching the focal distance to the user's gaze-defined target depth. Following prior work, we conducted a within-subject study with 24 participants performing an ISO 9241-411 pointing task under varifocal and fixed-focal viewing. Overall, varifocal viewing yielded significantly higher performance than the fixed-focal baseline across key interaction metrics, although the magnitude and even the direction of the benefit varied across individuals. In particular, participants' responses exhibited a baseline-dependent pattern, with smaller improvements (or occasional degradation) observed for those with better baseline performance. Our findings suggest that varifocal technology can improve AR pointing performance relative to fixed-focal viewing, while highlighting substantial individual differences that should be considered in design and evaluation.

Figures (11)

• Figure 1: The custom varifocal display. (Left) A user pointing at a virtual target with the wand input device, as viewed through the varifocal display. (Right) The components of the varifocal display. Green arrows represent light from the real scene, while red arrows represent light from the virtual image, reflected by the spherical mirror and beamsplitter. Both converge at the beamsplitter and enter the human eye together.
• Figure 2: Movement directions. (a) Lateral direction, with both virtual targets positioned 52.5 cm from the user; (b) depth direction, with virtual targets positioned 40 cm and 65 cm from the user, respectively. For both movements, the separation distance between the virtual targets is 25 cm.
• Figure 3: User study. (a) Experimental environment. (b) Wand. (c) An image of a user performing our experiment. (d) The revised setup, which improves mechanical robustness and ergonomics.
• Figure 4: Exemplary views with varifocal feature activated. The user focuses on the target shown at different distances: (a-c) at the closest plane, with the test pattern at the (a) closest, (b) middle, and (c) farthest plane; (d-f) at the farthest plane, with the test pattern at the (d) closest, (e) middle, and (f) farthest plane.
• Figure 5: Calibration views from the user's perspective, with the calibration platforms positioned at (a) 65 cm, (b) 52.5 cm, and (c) 40 cm from the user. The virtual and real calibration platforms are aligned at these points. (d) The three calibration platforms were placed on a height-adjustable table, allowing easy removal after each depth was calibrated.