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The efficacy of using point source lights to measure depth perception under remote view is evaluated. A Howard-Dolman type apparatus in which the depth plane is represented by either traditional rods or by point source lights is used. Ten operators, half viewing rods and half viewing lights, were asked to give depth scaling and stereoacuity judgments under four display conditions: (1) 2-D static, (2) 2-D motion parallax, (3) 3-D static, (4) 3-D motion parallax. The pattern of both stereoacuity and depth scaling responses was similar for rods and lights across the four conditions. Stereoacuity was significantly improved under 3-D as compared to 2-D view and under motion parallax as compared to static view for both lights and rods. When viewing lights but not rods a combination of motion parallax with disparity cues produced further improvements in stereoacuity. This pattern of results was similar for depth scaling, but differences were not significant. The accuracy of both stereoacuity and depth scaling judgments decreased when point source lights, as compared to rods, were viewed. These results show that point source lights produce valid measures of depth perception and contain fewer non-disparity cues than traditional Howard-Dolman rods.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In a recent paper we presented the formulation of multiple-frequency tomography with the Scanning Tomographic Acoustic Microscope (STAM) [1]. Because of the limited range of frequencies available, the STAM is not ideally suited for multiple-frequency tomography. In this paper we review the tomographic reconstruction algorithm and present the implementation of multiple-angle tomography. In addition to the projecdon phase correction required for multiple-frequency tomography [1], multiple-angle tomography also requires registration and alignment of the tomographic projections. By addressing the projection phase error and alignment problems, we have successfully implemented the STAM for multiple-angle tomography, and experimental reconstructions of a two-layer specimen are presented to demonstrate the feasibility and capability of the STAM.

Several investigators have reported that voluntary pursuit of a moving object is less smooth when it moves over a textured background compared with when it moves over a dark background. Furthermore, when a person fixates a stationary target on a moving background, microdrifts of the eyes occur in the direction of motion of the background. These two facts suggest that OKN is not completely switched off during voluntary pursuit or fixation. Howard and Simpson (1989) found that optokinetic nystagmus (OKN) is only weakly evoked by moving stimuli which are out of the plane of convergence. This led to the prediction that voluntary pursuit of a visual target should be disrupted more by a stationary background in the same depth plane than by a background which is nearer or further away than the pursuit target. Pursuit disruption was measured by the frequency and total amplitude of saccadic intrusions. For horizontal pursuit, disruption was reduced, compared with the coplanar condition, when the textured background was further away than the target but not when it was nearer. For vertical pursuit, disruption was reduced in both the far and near conditions compared with the coplanar condition. In both cases disruption was least when the background was dark.

A highly performance-enhanced three-dimensional (3D) object recognition system has been implemented using a computational integral imaging technique with depth of picked-up elemental images. For this, depth data of the picked-up elemental images are extracted, and elemental images are classified into a number of groups depending on these depth values. Then, each group of depth-dependently classified elemental images is separately used for reconstructing the object image on each corresponding depth plane. By this method, defocused images resulting from the objects located on other depth planes, which unavoidably occur in the conventional computational integral imaging reconstruction (CIIR) method, can be effectively removed. That is, in the proposed method, only the clearly focused object images can be reconstructed where the objects were originally located. Thus, a significant performance improvement of the CIIR-based 3D object recognition system is obtained. Experimental results confirm the feasibility of the proposed method.

The ability of human beings to shift their vergence between multiple disparity stimuli was investigated. The stimulus was a stereogram consisting of a single bar (1× 0.3°) projected in the center of a larger circular pattern (28° dia) of dots (0.3° dia). In the initial condition, the subjects perceived a single bar in the center of a cluster of dots, all lying in a single depth plane. The subjects were instructed to fixate either the bar or one of the dots close to the bar. Stepwise changes of target-vergence of either the bar, or of all dots, or of both configurations in opposite directions, were imposed in a random sequence. Under these conditions, ocular vergence was controlled by the target-vergence of the selected target at all times, even if this implied a loss of binocular fusion for the non-selected target. The effect of target selection per se, without concomitant changes in retinal position of the selected target, was studied in two experienced subjects with stabilized image techniques. The subjects viewed a configuration containing short vertical bars placed at either side of a long vertical bar. The short bars on different sides of the long bar had opposite (crossed or uncrossed) disparities. After stabilization of the configuration while the subject fixated the long bar, subjects attempted to fixate the short bars alternatingly. Due to the stabilization the ensuing eye movements did not affect the retinal positions, and thus the disparity, of the bars. Attempted fixation of a para-foveally viewed, short bar induced vergence responses in the appropriate direction. These vergence responses would have reduced disparity of the selected target if this had not been stabilized, at the expense of increasing disparity of non-selected targets. From this result we conclude that, by the mechanism of target selection, disparity information of the selected target is gated to a subsystem processing disparity which controls vergence.

When two sine-wave gratings drift in different directions at the same speed behind a circular window, a single coherent plaid is seen rather than one grating sliding over the other. We find that as the stereo depth separation of the two component gratings increases, the probability of seeing a plaid declines. The gain of the slow phase of vertical optokinetic nystagmus (OKN) also falls as the separation of the components increases. When the two grating components are in the same depth plane, the vertical eye velocity is greater than that of either component. This shows that the OKN is being driven by the plaid, whose vertical speed is roughly twice as fast as the components. We conclude that both perception and OKN are fed by the same motion signal, which arises after binocular combination and after plaid synthesis.

One of the major tasks faced by organisms in a complex environment is disambiguating the objects in that environment from their backgrounds and from each other. The task is already challenging when there are a few objects in view with multi-faceted surfaces covered with multicolored patterns and lit with varying degrees of light and shadow. This might be exemplified by a scene of bathers in multicolored swimwear on the beach. But the disambiguation becomes nearly impossible when the scene is a deeply three-dimensional one of foliage high in the trees of a thick forest. When primates first adopted such an arboreal habitat, they were faced with the task of locomotion through this three-dimensional realm of branches heavily masked by a veil of leaves. The stakes for disambiguating the true distances from tree to tree were high; the price of failure was to drop many meters onto a ground inhabited by carnivorous beasts.

Two experiments are described which examine the effect of distance in the depth plane, as defined operationally by binocular disparity, on focused and divided attention. In both experiments, disparity was manipulated with a Tektronix stereoscopic 3D display system. In Experiment 1 (focused attention), 10 subjects classified letter stimuli presented at zero disparity. The targets were surrounded, either vertically or horizontally, by two irrelevant stimuli. The distractors were presented at 7 different depth planes relative to the target (i.e., 3 in front, 3 behind, and 1 at the same depth). The distractors showed evidence of being processed when at the same depth plane as the central relevant stimulus, but diminished processing when presented at different depth planes. This pattern of data provides evidence for a fairly "narrow" attentional bandwidth in depth, for focused attention. In Experiment 2 (divided attention), 8 subjects performed a one-axis pursuit tracking task at 0 disparity, while concurrently responding to stimuli presented immediately below, and at 5different depth planes (1 at the same disparity as the tracking task, 2 in front of, and 2 behind the tracking display). While there was considerable interference between the two tasks, there was no evidence that this interference was modulated by similarity of depth when the depth plane of stimulus presentation was known in advance (i.e., was "blocked"). These results suggest that in divided attention, where stimulus location is known in advance, the attentional bandwidth in depth is sufficiently broad to accommodate the same range of depth planes over which filtering had been observed in focused attention. When however the depth plane was randomized and unpredictable, evidence for a depth gradient of divided attention was found. The results are discussed in terms of attentional theory and the usefulness of stereoscopic displays.

The experiments in this paper demonstrate that ‘‘Early Vision’’ mechanisms can account for the appearance of three ‘‘Diamond Wall’’ demonstrations, without reliance on apparent illumination, transparency, apparent depth, and junctions. The first set (Section 2) demonstrates that simultaneous contrast and the Katz– Albers effect can explain the appearance of a Diamond Wall display. The second set (Section 3) reviews the ‘‘Straight Edge’’ experiments designed to show changes in lightnesses consistent with perceived illumination. These experiments showed that very-low-spatialfrequency sampling causes both these effects, and White’s effect. The third set (Section 4) applies complex Early Vision models to images associated with the ‘‘High Vision’’ lightness hypotheses. The argument is that flat displays, which are perceived as flat, require a quite complex visual mechanism just to account for the properties of flat lightnesses. Any experimental verification of the existence of High Vision lightness mechanisms should be tested first with realistic complex Early Vision models. The results show that Early Vision mechanisms can account for appearances in Diamond Wall experiments. If Early Vision mechanisms can explain these results, then these experiments cannot be used as evidence for the existence of High Vision mechanisms.

Two experiments are reported which investigated the effects on stereopsis perception times of including monocularly conspicuous features in random-dot stereograms. It was found that such features facilitated stereopsis in large-disparity but not in small-disparity stereograms, perception times for the latter being relatively short with or without monocular features. Facilitation in the large-disparity stimuli came about both from features which delineated the shape of the whole disparate area and from features which merely happened to lie in the same depth plane as the disparate area, but which did not give any shape cues. It is argued that these various results can be well accounted for by a ‘vergence hypothesis’, which supposes that the long perception times often found with random-dot stereograms are due in part to the absence of stimulus features which can guide the vergence movements necessary for fusing the display.

The research in the present article was designed to investigate the phenomenon of stereoscopic transparency, in which overlapping surfaces are perceived simultaneously at different depths in the same visual direction. Four experiments are reported that examined observers’ abilities to achieve this phenomenon over a wide range of stimulus conditions. The results indicate that (1) the perceptual segregation of overlapping transparent surfaces is significantly more difficult than are comparable judgments for opaque surfaces; (2) the perception of transparency is impaired by increased depth differences between the overlapping surfaces or by increased element density; and (3) the effect is facilitated when the overlapping depth planes are distinguished by color, but not when they are distinguished by element orientation. The theoretical significance of these results is considered within the context of current competitive/cooperative models of stereo matching.

Based on the conventional ray‐tracing principle, a fast numerical algorithm is developed that calculates averaged propagation loss and reverberation of underwater sound. The averaging is performed by summing incoherently the contributions of individual ray bundles to each of the rectangular cells into which the range/depth plane is divided. The resulting matrix description of the average intensity field is used to calculate reverberation. The propagation‐loss algorithm is preliminarily tested against mathematical test functions and measured data.Subject Classification: [43]30.20, [43]30.40; [43]85.84.

Flickering areas of the visual field are perceived predominantly as backgrounds and the adjacent nonflickering areas are seen as figures. The effect of flicker on anchoring a region as ground is optimal within a limited range of temporal frequencies. Within the temporal frequencies used in the present experiments, the effect was greatest at 6.3 and 8.3 Hz. At these flicker rates the flickering regions were seen as ground over 75% of the time, whereas at 1.4 and 12.5 Hz the flickering regions were seen as ground less than 60% of the time. The average temporal luminance of the flickering and nonflickering areas was kept equal, so the figure-ground perception we found is not due to any luminance differences between the two regions. The flickering areas seen as ground were also perceived to lie on a depth plane behind the nonflickering figure regions. The amount of perceived depth separation increased as the regions became more perceptually anchored. The temporal tuning function offlicker-induced ground appears to be similar to those of visual pathways most sensitive to high temporal frequency.

A luminance gradient was constructed consisting of four successive steps of decreasing luminance which were staggered in depth. With monocular viewing, all steps appeared in the same apparent depth plane, and clear Mach bands were visible. With binocular viewing, however, the steps appeared to be at different distances, and Mach bands were greatly attenuated or absent even though each monocular view contained an adequate stimulus for their perception. Implications of this finding for retinal accounts of brightness contrast effects are discussed.

Stereoacuity and its dependence on contrast were measured at four spatial frequencies separated by 1 octave steps. Using a method of adjustment, observers adjusted the retinal disparity of an aperiodic narrow-band stimulus until it appeared in the depth plane defined by two flanking reference lines. Variations in contrast affected stereoacuity (the standard deviation of ten depth settings), with better performance observed at higher contrasts. Data were fit with straight lines (on a log–log plot), indicating a power-law dependence on contrast; the slope was steeper at lower spatial frequencies. These findings are consistent with the idea that disparity is computed from the responses of size-tuned mechanisms characterized by nonlinear contrast transfer functions. In a second experiment, the effects of interocular differences in contrast on stereoacuity were studied for two conditions. In the first condition, one eye always viewed a high-contrast target while the other eye viewed targets of successively lower contrast; in the second condition, one eye always saw a target of near-threshold contrast while the other eye saw targets of successively higher contrast. When the fixed contrast was high, stereoacuity deteriorated steadily as the interocular difference in contrast increased; the loss of stereoacuity was greatest at the lowest spatial frequency. When the fixed contrast was low, however, small increases in the contrast to one eye had no deleterious effect on stereoacuity. Once interocular contrast settings exceeded a certain difference, stereoscopic acuity began to deteriorate at lower spatial frequencies. These results address the issue of the stage of visual processing at which contrast exerts its influence on stereopsis.

Perceived depth was studied when an ambiguous stereopair (containing both crossed and uncrossed disparity) was viewed following exposure to an unambiguous stereopair (containing either crossed or uncrossed disparity). The “depth marker” effect (with the ambiguous figure seen in the same depth plane as the immediately preceding unambiguous figure) reported by Julesz (1964) was not replicated. Instead the ambiguous figure appeared near following exposure to uncrossed disparity and far after inspection of crossed disparity. This bias in depth judgments is attributed to disparity-selective masking ot a component within a compound stereospatial display.

Advances in the understanding of brain pathophysiology and the treatment of cerebral disorders are, in many respects, restricted by the development of associated technologies. This is illustrated by the paucity of reliable measurements of regional cerebral function which, until recently, have been limited to measurements of blood flow and of the general integrity of the blood brain barrier — using indicator dilution techniques and radioactive tracers. The restricted development of these techniques has been due to the virtual lack of spatial resolution of the various imaging devices in the depth plane and the limited choice of radio-actively labelled tracers.

Qualitative and quantitative scattering measurements at high acoustic frequencies were compared to the distributions of zooplankton, nekton, and other oceanographic measurements. Scattering was recorded at 100 and 200 kHz from depths of high euphauslid concentrations. No scattering was recorded at 11 kHz at these depths on some cruises. When scattering was recorded at 11 kHz at the depths of the high‐frequency scattering layer, the scattering records were qualitatively different and indicated the presence of fishes within the high‐frequency scattering layers. The high‐frequency scattering was also often correlated with oceanographic discontinuities such as thermoclines, haloclines, oxyclines, and the chlorophyll maximum. Variations in scattering strengths at the same depth plane were recorded. This patchiness in distribution of scattering at the high frequencies appeared to be correlated with aggregations of euphausiids. [Work supported by ONR.]

Perturbations in mode eigenvalues, associated with interactions between two ducts, were first investigated by the authors in 1969. The investigation of this interaction is extended to the frequency dependence of the coupling between ducts. A numerical measure of this coupling has been developed and used to determine optimum frequencies of propagation between a source located within one duct and a receiver located within the other duct. These optima occur near frequencies where the phase velocity difference between two adjacent modes forms a minimum. The coupling is strongly frequency dependent. For an example from the North Atlantic, one optimum frequency was found at 53.23 Hz. Propagation loss versus range plots show about 10 dB less loss at 53.23 Hz as compared to 64 Hz, where the mode phase velocities are well separated. Contour plots of propagation loss in the range‐receiver depth plane have been generated for a source in the upper duct. At 53.23 Hz these plots exhibit a range periodic transfer of ene...