Henry L. Apfelbaum

DLP-based dichoptic vision test system.

It can be useful to present a different image to each of the two eyes while they cooperatively view the world. Such dichoptic presentation can occur in investigations of stereoscopic and binocular vision (e.g., strabismus, amblyopia) and vision rehabilitation in clinical and research settings. Various techniques have been used to construct dichoptic displays. The most common and most flexible modern technique uses liquid-crystal (LC) shutters. When used in combination with cathode ray tube (CRT) displays, there is often leakage of light from the image intended for one eye into the view of the other eye. Such interocular crosstalk is 14% even in our state of the art CRT-based dichoptic system. While such crosstalk may have minimal impact on stereo movie or video game experiences, it can defeat clinical and research investigations. We use micromirror digital light processing (DLP) technology to create a novel dichoptic visual display system with substantially lower interocular crosstalk (0.3%; remaining crosstalk comes from the LC shutters). The DLP system normally uses a color wheel to display color images. Our approach is to disable the color wheel, synchronize the display directly to the computers sync signal, allocate each of the three (former) color presentations to one or both eyes, and open and close the LC shutters in synchrony with those color events.

Inattentional blindness and augmented-vision displays: effects of cartoon-like filtering and attended scene

Augmented‐vision devices that we are developing to aid people with low vision (impaired vision) employ vision multiplexing– the simultaneous presentation of two different views to one or both eyes. This approach enables compensation for vision deficits without depriving the wearers of their normal views of the scene. Ideally, wearers would make use of the simultaneous views to alert them to potential mobility hazards, without a need to divide attention consciously. Inattentional blindness, the frequent inability to notice otherwise‐obvious events in one scene while paying attention to another, overlapping, scene, works against that sort of augmentation, so we are investigating ways to mitigate it. In this study, we filtered the augmented view, creating cartoon‐like representations, to make it easier to detect significant features in that view and to minimise interference with the normal view. We reproduced a classic inattentional blindness experiment to evaluate the effect, and found that, surprisingly, edge filtering had no detectable effect – positive or negative – on the noticing of unexpected events in the unattended scene. We then modified the experiment to determine if the inattentional blindness was because of the confusion of overlaid views or simply a matter of attention, and found the latter to be the case.

Tracking the line of primary gaze in a walking simulator: Modeling and calibration

This article describes a system for tracking the line of primary gaze (LoPG) of participants as they view a large projection screen. Using a magnetic head tracker and a tracking algorithm, we find the onscreen location at which a participant is pointing a head-mounted crosshair. The algorithm presented for tracking the LoPG uses a polynomial function to correct for distortion in magnetic tracker readings, a geometric model for computing LoPG from corrected tracker measurements, and a method for finding the intersection of the LoPG with the screen. Calibration techniques for the above methods are presented. The results of two experiments validating the algorithm and calibration methods are also reported. Experiments showed an improvement in accuracy of LoPG tracking provided by each of the two presented calibration steps, yielding errors in LoPG measurements of less than 2° over a wide range of head positions. Source code for the described algorithms can be downloaded from the Psychonomic Society Web archive,http://www.psychonomic.org/archive/.

37.3: Dynamic Magnification of Video for People with Visual Impairment

Magnification is an effective aid for people with conditions causing resolution loss, but it inherently restricts the field of view. Therefore, magnification must be centered on the most important point of the scene. We determine this “point of regard” (POR) by recording eye movements of normal subjects while they watch video.

The risk of pedestrian collisions with peripheral visual field loss

Patients with peripheral field loss complain of colliding with other pedestrians in open-space environments such as shopping malls. Field expansion devices (e.g., prisms) can create artificial peripheral islands of vision. We investigated the visual angle at which these islands can be most effective for avoiding pedestrian collisions, by modeling the collision risk density as a function of bearing angle of pedestrians relative to the patient. Pedestrians at all possible locations were assumed to be moving in all directions with equal probability within a reasonable range of walking speeds. The risk density was found to be highly anisotropic. It peaked at ≈45° eccentricity. Increasing pedestrian speed range shifted the risk to higher eccentricities. The risk density is independent of time to collision. The model results were compared to the binocular residual peripheral island locations of 42 patients with forms of retinitis pigmentosa. The natural residual island prevalence also peaked nasally at about 45° but temporally at about 75°. This asymmetry resulted in a complementary coverage of the binocular field of view. Natural residual binocular island eccentricities seem well matched to the collision-risk density function, optimizing detection of other walking pedestrians (nasally) and of faster hazards (temporally). Field expansion prism devices will be most effective if they can create artificial peripheral islands at about 45° eccentricities. The collision risk and residual island findings raise interesting questions about normal visual development.

Volume Perimetry: measurement in depth of visual field loss

Purpose. Volume scotomas are three-dimensional regions of space that are not visible to the observer. Volume perimetry maps volume scotomas. Volume scotomas predicted from combining monocular visual fields assume known fixation locus (mainly foveal). However, fixation loci are not always known, especially with central field loss (CFL). Here we demonstrate methods for measuring and calculating volume scotomas and discuss their practical implications. Methods. Three patients (bitemporal hemianopia, binasal scotoma, and CFL) were evaluated. Slices through the volume scotomas were measured at three distances: at the plane of fixation, at a plane anterior to fixation (representing anterior volume perimetry), and at a plane posterior to fixation (representing posterior volume perimetry). For anterior volume perimetry, patients fixated on a screen 100 cm away through a beamsplitter that reflected the perimetric stimulus (at 50 cm). For posterior volume perimetry, patients fixated on a near target (50 cm), while perimetric stimuli were presented on a screen 150 cm beyond fixation. At the plane of fixation, monocular visual fields under binocular viewing conditions were measured using a computerized dichoptic perimeter. Results. Posterior and anterior volume scotomas were documented in patients with bitemporal hemianopia and binasal scotomas, respectively. The CFL patient demonstrated both anterior and posterior volume scotomas. Scotoma magnitude was considered to determine its effect on visual function. Conclusions. Direct measurement of volume scotomas can be performed. Anterior and posterior volume visual fields can vary substantially from conventional binocular perimetry measured at the fixation plane, revealing blind areas not otherwise identified. These volume scotomas are likely to impair functional vision such as driving (for bitemporal hemianopes) and near work with small hand tools (for binasal scotomas). Patients with CFL will have impaired functional vision for both distance and near tasks. Consideration of volume scotomas can help provide more effective vision rehabilitation and counseling.

41.2: The Effect Of Edge Filtering On Vision Multiplexing

We developed a video filter that produces cartoon-like images consisting of bipolar white and black transitions at luminance edges of the input video, for use in augmented-vision devices. When tested in an inattentional blindness experiment it had no effect on the detectability of unexpected events, but did affect speed of responses to the attended task Response time improved when the unattended scene was filtered and degraded when the attended scene was filtered.

Inattentional blindness with the same scene at different scales

People with severely restricted peripheral visual fields have difficulty walking confidently and safely in the physical environment. Augmented vision devices that we are developing for low‐vision rehabilitation implement vision multiplexing, providing two views of the same scene at two different scales (sizes), with a cartooned minified wide view overlaying a natural see‐through view. Inattentional blindness may partially limit the utility of these devices as low‐vision aids. Inattentional blindness, the apparent inability to notice significant but unexpected events in an unattended scene when attention is fixed on another scene, has classically been demonstrated by overlaying two unrelated game scenes, with unexpected events occurring in one scene while attention is maintained on the other scene by a distractor task. We hypothesized that context like that provided by the related wide view in our devices might mitigate inattentional blindness in a study with two simultaneous views of the same scene shown at different scales. It did not, and unexpected event detection rates were remarkably consistent with our and other mixed‐scene studies. Still, detecting about half of the unexpected events bodes well for our use of vision aids that employ vision multiplexing. Without the aids, is it likely that many more events would be missed.