Depth-of-Focus Affects 3D Perception in Stereoscopic Displays

Familiar size affects perception differently in virtual reality and the real world

The promise of virtual reality (VR) as a tool for perceptual and cognitive research rests on the assumption that perception in virtual environments generalizes to the real world. Here, we conducted two experiments to compare size and distance perception between VR and physical reality (Maltz et al. 2021 J. Vis. 21, 1-18). In experiment 1, we used VR to present dice and Rubik's cubes at their typical sizes or reversed sizes at distances that maintained a constant visual angle. After viewing the stimuli binocularly (to provide vergence and disparity information) or monocularly, participants manually estimated perceived size and distance. Unlike physical reality, where participants relied less on familiar size and more on presented size during binocular versus monocular viewing, in VR participants relied heavily on familiar size regardless of the availability of binocular cues. In experiment 2, we demonstrated that the effects in VR generalized to other stimuli and to a higher quality VR headset. These results suggest that the use of binocular cues and familiar size differs substantially between virtual and physical reality. A deeper understanding of perceptual differences is necessary before assuming that research outcomes from VR will generalize to the real world. This article is part of a discussion meeting issue 'New approaches to 3D vision'.

Optimizing Visual Performance With Digitally Assisted Vitreoretinal Surgery

BACKGROUND AND OBJECTIVE

Evaluate depth of field (DOF) and lateral resolution (LR) on digitally assisted vitreoretinal surgery (DAVS) with different camera aperture values and TV viewing distances to determine maximal optical performance.

PATIENTS AND METHODS

Five retinal surgeons objectively evaluated DOF and LR at low (10×), medium (15×), and high (20×) magnification on a conventional microscope (CM) and DAVS. DAVS was evaluated at different camera apertures (30%, 50%, and 75%) and TV viewing distances (1.2 meters [m], 1.5 m, and 2.0 m). A comparison between CM and optimized DAVS values was carried out.

RESULTS

On DAVS, DOF significantly increased as camera aperture size was reduced (75% to 50%, P = .022; 75% to 30%, P ≤ .001; and 50% to 30%, P = .001) and as microscope magnification was reduced (high to medium, P = .009; high to low, P ≤ .001; and medium to low, P = .002). LR significantly increased as microscope magnification was increased (low to medium, P = .010; low to high, P ≤ .001; and medium to high, P = .015) and as TV display distance decreased (2.0 m to 1.5 m, P = .019; 2.0 m to 1.2 m, P = .009; and 1.5 m to1.2 m, P = .185). When comparing optimized DAVS against CM, DOF was significantly larger on DAVS (P = .019). LR on DAVS outperformed the CM, but statistical significant was not reached (P = .185).

CONCLUSIONS

The authors' study is the first to evaluate different aperture, magnification, and TV distance settings, and when optimized, DAVS can significantly outperform a CM with respect to DOF and LR. Optimized visual performance for DAVS is obtained with a 30% camera aperture and a TV viewing distance no further than 1.5 m. Maximal microscope magnification to exploit LR during macular surgery and low-to-medium magnification to increase DOF for overall vitrectomy surgery is recommended. [Ophthalmic Surg Lasers Imaging Retina. 2020;51:S15-S21.].

RESOLUTION, DEPTH OF FIELD, AND PHYSICIAN SATISFACTION DURING DIGITALLY ASSISTED VITREORETINAL SURGERY

PURPOSE

To evaluate depth of field, lateral resolution, and image quality of a heads-up 3D visualization system for vitreoretinal surgery using physician survey and optical measurement outcomes.

METHODS

Depth of field and lateral resolution were compared between the standard ocular viewing system and the digital 3D system at ×5, ×13, and ×18 magnification by 6 retinal surgeons. Optical techniques were used as well as a survey of surgeon impression. Surgeon impression surveys were performed after 6 weeks of surgical use of the device.

RESULTS

Physician questionnaire survey scores for depth of field at high magnification were better for the digital 3D system and equivalent for all other categories. Measured lateral resolution was 36.7 mm and 16.6 mm at ×5 magnification (P < 0.001), 14.3 mm and 6.4 mm at ×13 magnification (P < 0.001), and 9.8 mm and 4.2 mm (P < 0.001) at ×18 magnification for the digital 3D and oculars, respectively. Measured depth of field was 4.00 mm and 6.78 mm at ×5 magnification (P = 0.027), 0.72 mm and 0.86 mm at ×13 (P = 0.311), and 0.28 mm and 0.40 mm at ×18 magnification (P = 0.235) for the oculars and digital 3D, respectively.

CONCLUSION

Lateral resolution of the digital 3D system was half that of the ocular viewing system and there was some improvement in depth of field with the digital system. Surgeon impression suggested that the digital system was superior when evaluating depth of field at high magnification.

(Disparity-Driven) Accommodation Response Contributes to Perceived Depth

When looking at objects at various distances in the physical space, the accommodation and vergence systems adjust their parameters to provide a single and clear vision of the world. Subtended muscle activity provides oculomotor cues that can contribute to the perception of depth and distance. While several studies have outlined the role of vergence in distance perception, little is known about the contribution of its concommitant accommodation component. It is possible to unravel the role of each of these physiological systems by placing observers in a situation where there is a conflict between accommodation and vergence distances. We thus sought to determine the contribution of each response system to perceived depth by simultaneously measuring vergence and accommodation while participants judged the depth of 3D stimuli. The distance conflict decreased depth constancy for stimulus displayed with negative disparity steps (divergence). Although vergence was unaffected by the stimulus distance, accommodation responses were significantly reduced when the stimulus was displayed with negative disparities. Our results show that biases in perceived depth follow undershoots in the disparity-driven accommodation response. These findings suggest that accommodation responses (i.e., from oculomotor information) can contribute to perceived depth.

The Role of Vertical Disparity in Distance and Depth Perception as Revealed by Different Stereo-Camera Configurations

Vertical binocular disparity is a source of distance information allowing the portrayal of the layout and 3D metrics of the visual space. The role of vertical disparity in the perception of depth, size, curvature, or slant of surfaces was revealed in several previous studies using cue conflict paradigms. In this study, we varied the configuration of stereo-cameras to investigate how changes in the horizontal and vertical disparity fields, conflicting with the vergence cue, affect perceived distance and depth. In four experiments, observers judged the distance of a cylinder displayed in front of a large fronto-parallel surface. Experiment 1 revealed that the presence of a background surface decreases the uncertainty in judgments of distance, suggesting that observers use the relative horizontal disparity between the target and the background as a cue to distance. Two other experiments showed that manipulating the pattern of vertical disparity affected both distance and depth perception. When vertical disparity specified a nearer distance than vergence (convergent cameras), perceived distance and depth were underestimated as compared with the condition where vertical disparity was congruent with vergence cues (parallel cameras). When vertical disparity specified a further distance than vergence, namely an infinite distance, distance and depth were overestimated. The removal of the vertical distortion lessened the effect on perceived distance. Overall, the results suggest that the vertical disparity introduced by the specific camera configuration is mainly responsible for the effect. These findings outline the role of vertical disparity in distance and depth perception and support the use of parallel cameras for designing stereograms.