Michael J. Sinai

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.

Diffuse and localized nerve fiber layer loss measured with a scanning laser polarimeter: sensitivity and specificity of detecting glaucoma.

Purpose: To differentiate normal from diseased retinal nerve fiber layers (NFL) using a new method of analyzing polarimetry data that specifically targets patterns of diffuse and localized NFL loss. Methods: The NFL from a sample of 34 patients with primary open‐angle glaucoma (POAG), 34 patients with ocular hypertension, and 34 normal subjects were imaged using a scanning laser polarimeter (GDx; Laser Diagnostic Technologies, Inc., San Diego, CA). Diffuse loss was defined as a reduction in the peak‐to‐trough amplitude of the double‐hump NFL pattern, and localized loss was defined as a lowering of the correlation of thickness values between local regions shown previously to correspond in normal subjects. Results: Significant differences were found between the groups of normal subjects, patients with hypertension, and patients for both the amplitude and the correlational measures. The sensitivity and specificity calculated using optimal criterion values were 94% and 91%, respectively. Conclusions: These results suggest that NFL analysis targeting specific patterns of loss may be beneficial for differentiating normal NFL patterns from diseased NFL patterns, as well as for identifying patients at high risk.

Fourier analysis of nerve fiber layer measurements from scanning laser polarimetry in glaucoma: emphasizing shape characteristics of the 'double-hump' pattern.

Purpose: The pattern of the distribution of nerve fiber layer (NFL) thickness values across the retina may provide an early anatomic indication of glaucomatous disruption. We developed a method of analyzing polarimetry measurements that emphasizes the shape of the pattern of NFL thickness values. Sensitivity and specificity for detecting glaucoma was obtained for these measures and compared with those for conventional measures. Methods: Nerve fiber thickness was inferred from retardation shift measured by a scanning laser polarimeter (Laser Diagnostic Technologies, Inc., San Diego, CA) in 34 healthy subjects (68 eyes) and 34 patients with glaucoma (68 eyes). Fourier analysis was performed on the polarimetry data to emphasize the shape in the evaluation of the distribution of thickness values around the optic disc (along a 1.7‐disc diameter ring). This was computed separately on superior and inferior hemiretinas. Results: Significant differences were found in the Fourier shape measures between healthy subjects and patients with glaucoma. The sensitivity and specificity using Fourier coefficients with this particular sample was 96% and 90%, respectively. Conclusion: The evaluation of NFL measurements with Fourier analysis to emphasize the holistic shape of the “double‐hump” pattern was found to be a useful tool as an analysis strategy.

Interocular symmetry in nerve fiber layer thickness of normal eyes as determined by polarimetry.

PURPOSE The existence of asymmetries between the two eyes in number and distribution of nerve fibers may provide an early anatomic indication of glaucomatous disruption if a symmetrical pattern of nerve fibers can be shown in normal eyes. Normal eyes were tested to determine whether a high degree of correspondence of regional nerve fiber layer thickness exists between fellow eyes. METHODS Nerve fiber layer thickness was inferred from retardation shift measured by a scanning laser polarimeter (Laser Diagnostic Technologies, Inc.) in 40 volunteers without glaucoma or ocular disease (80 eyes). Total thickness and the pattern of nerve fiber thickness over 208 regions was compared between the paired eyes. RESULTS Inferred nerve fiber layer thickness in companion eyes was highly correlated. Variation of the total nerve fiber thickness was much less between companion eyes than between eyes of different individuals. In terms of regional (i.e., local) interocular correspondence, the measurements in the inferior retina were observed to be highly similar in the two eyes, but a pronounced shift of the location of the superior peak (maximum thickness) in the left eye relative to the right was observed, as were differences between the two eyes in the thickness measurements at the nasal and temporal minima. CONCLUSION Significant interocular asymmetries were detected in regions other than the interior hemiretina. These interocular asymmetries may reflect previously unrecognized anatomic nerve fiber differences or systematic angular bias in the instrument for one eye relative to the other. In contrast to the regional measures, the measures of total thickness were very similar between companion eyes, suggesting that the assessment of interocular asymmetries of total thickness determined by polarimetry may offer potential for detecting glaucoma.

Human Perceptual Performance With Nonliteral Imagery: Region Recognition and Texture-Based Segmentation

In this study the authors address the issue of how the perceptual usefulness of nonliteral imagery should be evaluated. Perceptual performance with nonliteral imagery of natural scenes obtained at night from infrared and image-intensified sensors and from multisensor fusion methods was assessed to relate performance on 2 basic perceptual tasks to fundamental characteristics of the imagery. Specifically, single-sensor imagery and fused multisensor imagery (both achromatic and false color) were used to test performance on a region recognition task and a texture segmentation task. Results indicate that the use of color rendering and type of scene content play specific roles in determining perceptual performance allowed by nonliteral imagery. The authors argue that the usefulness of various image-rendering methods should be evaluated with respect to multiple perceptual tasks.

Effect of age and disc size on rim order rules by Heidelberg Retina Tomograph.

Purpose:The ISNT rule for nonglaucomatous eyes suggests that the neuroretinal rim is thickest at the inferior quadrant (I), followed by the superior (S), nasal (N), and temporal (T) quadrants. This study aimed to use Heidelberg Retina Tomograph (HRT III) measurements to assess (a) fulfillment of the ISNT rule and its derivatives in a large normative database and (b) effect of disc size and age on rule fulfillment. Patients and Methods:A multicenter, prospective, cross-sectional study of a Caucasian normative database consisting of 280 subjects with normal comprehensive biomicroscopic examination, intraocular pressure <21 mm Hg, and normal automated visual field testing was conducted. Right eye neuroretinal rim and disc area, measured by HRT III, for each of the 4 quadrants were analyzed. Compliance of the rim area to the ISNT rule (I≥S≥N≥T) and its derivates was determined. Effect of age and disc area on rule compliance was further determined. Results:Only 18% of normal eyes had rim areas that complied with the ISNT rule; however, a majority complied to IS (77%) and IST (73%) rules. The temporal quadrant had the smallest rim area [(I,S,N)>T] in 91% of patients. The likelihood of ISNT rule violation was increased in larger discs (&khgr;2, P=0.003) but was not affected by age. Conclusions:The ISNT rule does not apply to neuroretinal rim area as measured by HRT, as only 18% of the eyes complied with the ISNT rule in this normative database. Although the ISNT rule may be more applicable to normal eyes with a smaller disc area, the IS and IST rules seem to better represent the normative database.

Relevant spatial frequency information in the texture segmentation of night-vision imagery

We investigated the type of spatial structure present in nighttime imagery that is perceptually relevant for human observers to be able to perform texture-based segmentation of real world scenes. Three psychophysical tasks were developed to evaluate performance of the nighttime imagery. The test imagery consisted of scenes obtained via an image-intensified low=light CCD, a long-wave infrared sensor and monochrome sensor-fusion. For one task, performance was best with the fused imagery, but for two tasks, performance with fused imagery was not improved (compared to performance with ir imagery). Spatial filtering of the scenes and further testing revealed that the mid spatial frequencies (1-4 cpd) were more critical in determining performance than either the low or high frequencies. Fourier analysis of the scenes revealed a strong relationship between power and performance, where scenes with more power (especially at the middle frequencies) supported better performance. Implications of this research are that performance depends on power at the middle frequencies for those low-level visual tasks and that fusion algorithms may be improved if this is taken under consideration.

Extensions of the Sustained-Like and Transient-Like Effects

We report physiological and psychophysical studies that further expand and delineate two of the tests of Enoch’s Layer-by-Layer Perimetry. In the physiological studies we show that single ganglion cells give responses comparable to human responses. In the human studies we demonstrate that a corresponding sensitization response exists in the OFF-channel, that a “pure” flicker mechanism smaller than the transient-like mechanism exists, and that an orientation bias exists in the cortical properties mapped with a variation of these tests. These results offer extensions of layer-by-layer perimetry for the clinical testing of additional layers of the visual system.