Humans and many animals have forward-facing eyes providing different views of the environment. Precise depth estimates can be derived from the resulting binocular disparities, but determining which parts of the two retinal images correspond to one another is computationally challenging. To aid the computation, the visual system focuses the search on a small range of disparities. We asked whether the disparities encountered in the natural environment match that range. We did this by simultaneously measuring binocular eye position and three-dimensional scene geometry during natural tasks. The natural distribution of disparities is indeed matched to the smaller range of correspondence search. Furthermore, the distribution explains the perception of some ambiguous stereograms. Finally, disparity preferences of macaque cortical neurons are consistent with the natural distribution.

We present a probabilistic model of how viewers may use defocus blur in conjunction with other pictorial cues to estimate the absolute distances to objects in a scene. Our model explains how the pattern of blur in an image together with relative depth cues indicates the apparent scale of the image's contents. From the model, we develop a semiautomated algorithm that applies blur to a sharply rendered image and thereby changes the apparent distance and scale of the scene's contents. To examine the correspondence between the model/algorithm and actual viewer experience, we conducted an experiment with human viewers and compared their estimates of absolute distance to the model's predictions. We did this for images with geometrically correct blur due to defocus and for images with commonly used approximations to the correct blur. The agreement between the experimental data and model predictions was excellent. The model predicts that some approximations should work well and that others should not. Human viewers responded to the various types of blur in much the way the model predicts. The model and algorithm allow one to manipulate blur precisely and to achieve the desired perceived scale efficiently.

Summary Estimating depth from binocular disparity is extremely precise and the cue does not depend on statistical regularities in the environment. Thus, disparity is commonly regarded as the best visual cue for determining 3D layout. But depth from disparity is only precise near where one is looking; it is quite imprecise elsewhere [1-4]. To overcome this imprecision away from fixation, vision resorts to using other depth cues—e.g., linear perspective, familiar size, aerial perspective. But those cues depend on statistical regularities in the environment and are therefore not always reliable [5]. Depth from defocus blur relies on fewer assumptions and has the same geometric constraints as disparity [6], but different physiological constraints [7-14]. Hence, blur could in principle fill in the parts of visual space where disparity is imprecise [15]. We tested this possibility with a depth-discrimination experiment. We found that disparity was more precise near fixation and that blur was indeed more precise away from fixation. When both cues were available, observers relied on the more informative one. Blur appears to play an important, previously unrecognized [16,17] role in depth perception. Our findings lead to a new hypothesis about the evolution of slit-shaped pupils and have noteworthy implications for the design and implementation of stereo 3D viewing systems.

From the desktop to the laptop to the mobile device, personal computing platforms evolve over time. Moving forward, wearable computing is widely expected to be integral to consumer electronics and beyond. The primary interface between a wearable computer and a user is often a near-eye display. However, current generation near-eye displays suffer from multiple limitations: they are unable to provide fully natural visual cues and comfortable viewing experiences for all users. At their core, many of the issues with near-eye displays are caused by limitations in conventional optics. Current displays cannot reproduce the changes in focus that accompany natural vision, and they cannot support users with uncorrected refractive errors. With two prototype neareye displays, we show how these issues can be overcome using display modes that adapt to the user via computational optics. By using focus-tunable lenses, mechanically actuated displays, and mobile gaze-tracking technology, these displays can be tailored to correct common refractive errors and provide natural focus cues by dynamically updating the system based on where a user looks in a virtual scene. Indeed, the opportunities afforded by recent advances in computational optics open up the possibility of creating a computing platform in which some users may experience better quality vision in the virtual world than in the real one.virtual reality | augmented reality | 3D vision | vision correction | computational optics E merging virtual reality (VR) and augmented reality (AR) systems have applications that span entertainment, education, communication, training, behavioral therapy, and basic vision research. In these systems, a user primarily interacts with the virtual environment through a near-eye display. Since the invention of the stereoscope almost 180 years ago (1), significant developments have been made in display electronics and computer graphics (2), but the optical design of stereoscopic near-eye displays remains almost unchanged from the Victorian age. In front of each eye, a small physical display is placed behind a magnifying lens, creating a virtual image at some fixed distance from the viewer (Fig. 1A). Small differences in the images displayed to the two eyes can create a vivid perception of depth, called stereopsis.However, this simple optical design lacks a critical aspect of 3D vision in the natural environment: changes in stereoscopic depth are also associated with changes in focus. When viewing a near-eye display, users' eyes change their vergence angle to fixate objects at a range of stereoscopic depths, but to focus on the virtual image, the crystalline lenses of the eyes must accommodate to a single fixed distance ( Fig. 2A). For users with normal vision, this asymmetry creates an unnatural condition known as the vergence-accommodation conflict (3, 4). Symptoms associated with this conflict include double vision (diplopia), compromised visual clarity, visual discomfort, and fatigue (3, 5). Moreover, a lack of accurate focus also removes a cu...

Depth estimates from disparity are most precise when the visual input stimulates corresponding retinal points or points close to them. Corresponding points have uncrossed disparities in the upper visual field and crossed disparities in the lower visual field. Due to these disparities, the vertical part of the horopter—the positions in space that stimulate corresponding points—is pitched top-back. Many have suggested that this pitch is advantageous for discriminating depth in the natural environment, particularly relative to the ground. We asked whether the vertical horopter is adaptive (suited for perception of the ground) and adaptable (changeable by experience). Experiment 1 measured the disparities between corresponding points in 28 observers. We confirmed that the horopter is pitched. However, it is also typically convex making it ill-suited for depth perception relative to the ground. Experiment 2 tracked locations of corresponding points while observers wore lenses for 7 days that distorted binocular disparities. We observed no change in the horopter, suggesting that it is not adaptable. We also showed that the horopter is not adaptive for long viewing distances because at such distances uncrossed disparities between corresponding points cannot be stimulated. The vertical horopter seems to be adaptive for perceiving convex, slanted surfaces at short distances.