Abstract
Purpose :
Vergence-accommodation conflicts (VAC) occur when the visual system receives a mismatch between vergence and accommodation cues. In augmented reality (AR), VAC mainly manifests when switching focus between real world and AR content, and is a major challenge for AR devices. In our study, we developed a novel metric, time to focus (TTF), and quantified the impact of VAC and additive contrast on visual performance in AR.
Methods :
Sixteen participants (21 to 41 years; mean 29.4 ± 5.8 SD) with corrected-to-normal vision participated in the study. Visual stimuli were generated by a three-plane variable focus haploscope. Each trial consisted of two intervals and simulated switching focus from real world to AR content. In the first interval, we presented a 10 arcmin Landolt C on 1/f noise in the center of the visual field. Its focal and vergence distances were matched (no VAC) and set to 1D. In the second interval, another Landolt C with flankers appeared above or below the first C. The vergence distance of the second C was also 1D; however, its focal distance varied between 2.5D and 0D to induce variable degrees of VAC (including 1D as a no VAC control condition). In addition, the second C also varied in additive contrast ranging from 1.6:1 to 12:1. The task in both intervals was to identify the orientation of the C opening in four cardinal directions. The duration of the first interval was unlimited and a correct response triggered the second interval. The duration of the second interval was varied by an adaptive staircase to determine the TTF. The TTFs were normalized as % change from the control no VAC condition.
Results :
The main finding was that the TTF exponentially increased as a function of VAC (effect of VAC in ANOVA F6,90 = 18.1, p < 0.001). Furthermore, the TTF increase was exacerbated by reducing the additive contrast (interaction between VAC and contrast F18,270 = 5.8, p < 0.001). This trend was most pronounced at closer vergence distances reaching an average of 156.3% (± 33.7) increase in TTF at 2.5 D vergence distance.
Conclusions :
In this study we developed a novel metric to quantify the impact of AR VAC and additive on visual performance. We showed that VAC increases TTF which is further exacerbated by reduced additive contrast. More research is warranted to understand how these observations contribute to visual fatigue associated with usage of augmented reality devices.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.