Eric L. Heft

Psychophysical measurement of night vision goggle noise

Pilots, developers, and other users of night-vision goggles (NVGs) have pointed out that different NVG image intensifier tubes have different subjective noise characteristics. Currently, no good model of the visual impact of NVG noise exists. Because it is very difficult to objectively measure the noise of a NVG, a method for assessing noise subjectively using simple psychophysical procedures was developed. This paper discusses the use of a computer program to generate noise images similar to what an observer sees through an NVG, based on filtered white noise. The images generated were based on 1/f (where f is frequency) filtered white noise with several adjustable parameters. Adjusting each of these parameters varied different characteristics of the noise. This paper discusses a study where observers compared the computer-generated noise images to true NVG noise and were asked to determine which computer-generated image was the best representation of the true noise. This method was repeated with different types of NVGs and at different luminance levels to study what NVG parameters cause variations in NVG noise.

Optometric measurements predict performance but not comfort on a virtual object placement task with a stereoscopic three-dimensional display

Abstract. Twelve participants were tested on a simple virtual object precision placement task while viewing a stereoscopic three-dimensional (S3-D) display. Inclusion criteria included uncorrected or best corrected vision of 20/20 or better in each eye and stereopsis of at least 40 arc sec using the Titmus stereotest. Additionally, binocular function was assessed, including measurements of distant and near phoria (horizontal and vertical) and distant and near horizontal fusion ranges using standard optometric clinical techniques. Before each of six 30 min experimental sessions, measurements of phoria and fusion ranges were repeated using a Keystone View Telebinocular and an S3-D display, respectively. All participants completed experimental sessions in which the task required the precision placement of a virtual object in depth at the same location as a target object. Subjective discomfort was assessed using the simulator sickness questionnaire. Individual placement accuracy in S3-D trials was significantly correlated with several of the binocular screening outcomes: viewers with larger convergent fusion ranges (measured at near distance), larger total fusion ranges (convergent plus divergent ranges, measured at near distance), and/or lower (better) stereoscopic acuity thresholds were more accurate on the placement task. No screening measures were predictive of subjective discomfort, perhaps due to the low levels of discomfort induced.

Psychophysical measurement of night vision goggle noise using a binocular display

Users of night vision goggles (NVGs) have reported differences in perceived noise across various NVGs. To understand these differences, we need to measure NVG noise in a psychophysical context. In the precursory study, subjects attempted to characterize NVG noise by examining choices across different parameters of filtered white noise generated on a computer monitor. Subjects adjusted parameters of the filtered noise to match the noise for each combination of two goggles and two luminance levels. Significant differences were found between luminance levels, NVG type, and parameter relationships. Concerns from the previous experiment have yielded this study to better understand if this characterization process has merit. In the previous study, the parameter sequence was constant across trials. We increased the number of trials and subjects, and we included an accounting for parameter sequence. In addition, we used a modified Wheatstone stereoscope to simulate NVG tube independence. We discuss our results in terms of luminance levels, parameter sequence, subject variability, and relationships between parameters.

Chromaticity and luminance requirements for colored symbology in night vision goggles

Recent advances in display technology have made it possible to superimpose color-coded symbology on the images produced by night vision goggles (NVGs). The resulting color mixture shifts the symbologys hue and saturation, which can impede recognition of the color code. We are developing luminance-contrast specifications for color-coded NVG symbology to ensure accurate color recognition.

Luminance contrast requirements for colored symbols in helmet-mounted displays

Previously, we presented an experiment in which we defined minimum, but not sufficient, luminance contrast ratios for color recognition and legibility for helmet-mounted display (HMD) use. In that experiment, observers made a subjective judgement of their ability to recognize a color by stopping the incremental increase in contrast ratio of a static display. For some target color/background combinations, there were extremely high error rates and in these cases sufficient contrast ratios were not achieved. In the present experiment, we randomly presented one of three target colors on one of five backgrounds. The contrast ratio of the target on the background ranged from 1.025:1 up to 1.3:1 in steps of 0.025. As before, we found that observers could accurately identify the target colors at very low contrast ratios. In addition, we defined the range in which color recognition and legibility became sufficient (>= 95% correct). In a second experiment we investigated how ell observers did when more than one color appeared in the symbology at one time. This allowed observers to compare target colors against each other on the five backgrounds. We discuss our results in terms of luminance contrast ratio requirements for both color recognition as well as legibility in HMDs.

Investigations into optimal color and shape primitives using the Perspecta 3D volumetric display

Volumetric displays allow users to view freely three-dimensional (3D) imagery without special eyewear. However, due to low display resolution, many colors appear distorted compared to their representation on a flat-panel display. In addition, due to the unique nature of the display, some shapes, objects, and orientations can also appear distorted. This study examines the perceptual range of virtual objects in a Perspecta 3D volumetric display to determine which combination of object type, size, position, and color produces the best perceived 3D image. Across three experiments, we test different object types, hues, saturation levels of hues, and position within the volumetric display. Participants rated their hue and shape naming confidence as well as their ratings on solidity. Various significant main and interaction effects were exhibited among three separate experiments.

How much camera separation should be used for the capture and presentation of 3D stereoscopic imagery on binocular HMDs

Designers, researchers, and users of binocular stereoscopic head- or helmet-mounted displays (HMDs) face the tricky issue of what imagery to present in their particular displays, and how to do so effectively. Stereoscopic imagery must often be created in-house with a 3D graphics program or from within a 3D virtual environment, or stereoscopic photos/videos must be carefully captured, perhaps for relaying to an operator in a teleoperative system. In such situations, the question arises as to what camera separation (real or virtual) is appropriate or desirable for end-users and operators. We review some of the relevant literature regarding the question of stereo pair camera separation using deskmounted or larger scale stereoscopic displays, and employ our findings to potential HMD applications, including command & control, teleoperation, information and scientific visualization, and entertainment.

Color and shape perception on the Perspecta 3D volumetric display

Volumetric displays allow users to view freely three-dimensional (3D) imagery without special eyewear. However, due to low display resolution, many colors appear distorted compared to their representation on a flat-panel display. In addition, due to the unique nature of the display, some shapes, objects, and orientations can also appear distorted. This study examines the perceptual range of virtual objects in a Perspecta 3D volumetric display to determine which combination of object type, size, and color produces the best 3D image. Participants viewed combinations composed of three object types (vertical square plane, empty cube, filled cube) x three sizes (small, medium, large) x seven colors (aqua, blue, green, purple, red, white, yellow). They named the color of the object and then rated the uniformity of the color, the quality of the shape, amount of visual flicker, and the solidity of the object. All dependent measures except the rating of solidity exhibited various main and interaction effects among object type, size, and color.

Characterizing night vision goggle noise using the method of paired comparisons

Users of night vision goggles (NVGs) have reported differences in NVG noise across different as well as the same type of NVG. To better understand these differences, we attempted to characterize NVG noise by having subjects choose parameters in an NVG simulation to best match the noise in real NVGs. From our previous efforts, we observed interdependence of simulation parameters and variability across observers. This has lead us to use the method of paired comparisons as a process for characterizing NVG noise. The results suggest that people perceive NVG noise differently in terms of spatial, temporal, and contrast combinations. In addition, we provide a methodology for determining psychophysically the best parameter combinations in a simulation’s algorithm to match the real environment that the simulation represents.

Microstereopsis is good, but orthostereopsis is better: precision alignment task performance and viewer discomfort with a stereoscopic 3D display

Two separate experiments examined user performance and viewer discomfort during virtual precision alignment tasks while viewing a stereoscopic 3D (S3D) display. In both experiments, virtual camera separation was manipulated to correspond to no stereopsis cues (zero separation), several levels of microstereopsis (20, 40, 60, and 80%), and orthostereopsis (100% of interpupillary distance). Viewer discomfort was assessed before and after each experimental session, measured subjectively via self-report on the Simulator Sickness Questionnaire (SSQ). Objective measures of binocular status (phoria and fusion ranges) and standing postural stability were additionally evaluated pre and postsessions. Overall, the results suggest binocular fusion ranges may serve as useful objective indicators of discomfort from S3D viewing, perhaps as supplemental measures to standard subjective reports. For the group as a whole, the S3D system was fairly comfortable to view, although roughly half of the participants reported some discomfort, ranging from mild to severe, and typically with the larger camera separations. Microstereopsis conferred significant performance benefits over the no-stereopsis conditions, so microstereoscopic camera separations might be of great utility for non-critical viewing applications. However, performance was best with near-orthostereoscopic or orthostereoscopic camera separations. Our results support the use of orthostereopsis for critical, high-precision manual spatial tasks performed via stereoscopic 3D display systems, including remote surgery, robotic interaction with dangerous or hazardous materials, and related teleoperative spatial tasks.