Comparison of Light Field and Conventional Near-Eye AR Displays in Virtual-Real Integration Efficiency

Introduction

Existing augmented and virtual reality (AR/VR) devices often suffer from vergence-accommodation conflicts (VAC). Accommodation refers to the adjustment of focal length of a human eye to obtain a clear image of an object, whereas vergence refers to the simultaneous movement of both eyes towards or away from one another in order to align the two retinal images of an object on corresponding retinal points of interest. Consistent accommodation and vergence cues received by the brain can guide the eyes to properly focus on the object. A vergence-accommodation conflict (VAC) occurs when the brain receives mismatching vergence and accommodation cues (Figure 2), which can cause binocular fusion difficulty, visual fatigue, and dizziness to users of augmented and virtual reality (AR/VR). The conflict is more pronounced when the virtual object is closer to the eyes.

Figure 1.

We present a series of text-based visual search tasks to systematically and quantitatively test human visual performance under the influence of vergence-accommodation conflict (VAC). From left to right: experimental setup, example visual content, and experimental results. Each visual content example includes two side-by-side text blocks. The left text block is displayed by a smartphone, and the right text block by a pair of AR glasses.

Figure 2.

Illustration of the vergence-accommodation conflict. The eyes accommodate and converge at the same distance when watching a real object. But this is not the case when using a conventional 3D AR display.

Conventional augmented reality (AR) optical see-through displays render stereoscopic images on 2D image planes. These displays are notable for lacking the ability to provide correct focus cues for both accommodation and convergence. Unlike traditional stereoscopic techniques, light field displays, which are VAC-free, work by generating a light field pertaining to a virtual object and projecting it into the user’s eyes in the same way as the light field of a real object would travel to the eyes. A light field is a collection of light rays traveling from every point in the space of interest through every possible path (Levoy & Hanrahan, 1996). Since the light field display has continuous focal planes, the user can perceive a clear image of the virtual object at any depth.

The effect of VAC on users has been investigated for conventional AR glasses. While most of the work focuses on the physiological discomfort of users (Hoffman et al., 2008; Shibata et al., 2011; Zou et al., 2015), only a limited amount of work has examined the association between VAC and user visual performance (Gabbard et al., 2019; Daniel & Kapoula, 2019). Furthermore, light field AR display has never been considered in these studies. This motivates us to carry out the research further.

In this work, we design a psychovisual experiment to systematically and quantitatively compare the visual performance of participants wearing a pair of light field AR glasses with that of the same participants wearing a pair of conventional AR glasses. To the best of our knowledge, our work is among the first that systematically compare light field AR glasses (VAC-free) with conventional AR glasses (VAC-inherent). We want to find out whether there is a significant difference in user performance between light field AR glasses and conventional AR glasses under the same viewing condition. The results obtained in this experiment lays the foundation for future evaluation of near-eye light field displays.

Background

This section reviews the occurrence of VAC, the advanced architecture of conventional 3D displays, light field, and related works based on visual search tasks.