Visibility of road hazards in thermal, visible, and sensor-fused night-time imagery.

Sensor fusion combines the output of multiple imaging sensors within a single composite display. Ideally, a fused image will retain important spatial information provided by individual input images, and will convey useful spatial or chromatic emergent information derived from the contrast between input images. The present experiment assessed the potential benefits of sensor fusion as a method of enhancing drivers' night-time detection of road hazards. Observers were asked to detect a pedestrian within thermal and visible images of a night-time scene, and within chromatic and achromatic renderings created by sensor fusion of grayscale thermal and visible images. Results indicated that fusion can both improve spatial image content, and can effectively embellish spatial content with emergent chromatic information. The benefits of both sensor fusion and of color rendering, however, were inconsistent, varying substantially with quality of input images submitted for fusion.

An oblique effect of chromatic gratings measured by color-mixture thresholds.

Contrast sensitivity is lower for obliquely oriented achromatic gratings than for vertical or horizontal gratings at high spatial and low temporal frequencies. Although this response is suggestive of mediation by P-pathway cortical correlates, no clear sensory (i.e. class 1) oblique effect has been demonstrated with isoluminant chromatic stimuli. In the present experiment, a two-alternative forced-choice detection task was used to measure observers' sensitivity to spatiotemporal sinusoids varying in orientation and color contrast. A maximum-likelihood method fit ellipses to the thresholds, with the length of each ellipse taken as a measure of chromatic contrast sensitivity at isoluminance, and the width as luminance contrast threshold. A chromatic oblique effect was observed at about 3 cycles deg-1 suggesting an orientation bias within the cortical stream conveying P-cell activity.

Perceptual ability with real-world nighttime scenes: image-intensified, infrared, and fused-color imagery.

We investigated human perceptual performance allowed by relatively impoverished information conveyed in nighttime natural scenes. We used images of nighttime outdoor scenes rendered in image-intensified low-light visible (i2) sensors, thermal infrared (ir) sensors, and an i2/ir fusion technique with information added. We found that nighttime imagery provides adequate low-level image information for effective perceptual organization on a classification task, but that performance for exemplars within a given object category is dependent on the image type. Overall performance was best with the false-color fused images. This is consistent with the suggestion in the literature that color plays a predominate role in perceptual grouping and segmenting of objects in a scene and supports the suggestion that the addition of color in complex achromatic scenes aids the perceptual organization required for visual search. In the present study, we address the issue of assessment of perceptual performance with alternative night-vision sensors and fusion methods and begin to characterize perceptual organization abilities permitted by the information in relatively impoverished images of complex scenes. Applications of this research include improving night vision, medical, and other devices that use alternative sensors or degraded imagery.

Effects of mission rehearsal simulation on air-to-ground target acquisition.

Traditionally military aviators have prepared for air-to-ground bombing missions with maps and aerial photographs of their targets. Mission rehearsal systems augment these media by allowing pilots to view simulated ingress to their target, as seen from the cockpit perspective. In the present experiment we assessed the benefits of mission rehearsal with a task requiring observers to view recorded approaches to target objects and to detect the target objects as quickly as possible. Results indicated that premission simulations allowed observers to detect target objects at greater stand-off ranges than did study with maps and aerial photographs alone. Actual or potential applications of this research include the deployment of a mission rehearsal system to assist aviators' mission planning.

Binocular function in early glaucoma.

PURPOSE: This study investigated whether certain binocular mechanisms are disrupted in early glaucoma. METHODS: Glaucoma patients, suspects, and normals were tested on a battery of psychophysical tests consisting of flicker sensitivity (5 and 34 Hz), temporal cut-off frequency (CFF), contrast sensitivity (Pelli-Robson chart), and stereoacuity. Monocular channels were evaluated with tests of monocular flicker performance and spatial contrast sensitivity. Binocular summation on spatial and temporal tests was used to reflect integrity of binocular neural interactions. Stereoacuity was taken as a measure of performance of disparity processing mechanisms. RESULTS: The groups differed in terms of binocular flicker sensitivity at both temporal rates, binocular and monocular peak contrast sensitivity, and stereoacuity. Binocular summation of both spatial and temporal sensitivity was normal. The glaucoma suspect group was distinguishable from the age-matched normal group on binocular contrast sensitivity and stereoacuity. CONCLUSIONS: The binocular mechanisms that mediate stereoacuity appear to be heavily disrupted, whereas the binocular mechanisms that mediate central neural interaction of monocular inputs are normal. Although monocular spatiotemporal abilities are disrupted, the binocular processes combine the monocular input normally. In addition, our results suggest a benefit of binocular testing for routine assessment of glaucoma patients. The profound disruption of stereoacuity appears to result from disorder in the spatial sampling array at the ganglion-cell level similar to the disorder reported in the normal periphery and the central retina of strabismic amblyopes. These and previous findings were reviewed to evaluate the supposition of preferential M-pathway disruption in early glaucoma. Such a model can not be reconciled with the present findings. We conclude that measurements of temporal modulation sensitivity fit well with such a model, but that the current evidence of spatiotemporal contrast sensitivity disruption is less supportive of such a model.

An anisotropy of human tactile sensitivity and its relation to the visual oblique effect.

The ability of humans to detect striated stimuli on the distal phalanges was found to be highly anisotropic. Observers were much more sensitive to stripes presented in the proximal-distal orientation than to stripes in any other orientation. This tactile anisotropy was contrasted with the well-known visual anisotropy in which sensitivity is greatest for stripes at the horizontal and vertical orientations. We suggest that both the tactile anisotropy and the visual anisotropy are caused by corresponding anisotropies in the distribution of preferred orientations of orientation-selective neurons with in the respective modalities.