Binocular Luster Research Articles

Binocular luster elicited by isoluminant chromatic stimuli relies on mechanisms similar to those in the achromatic case.

The phenomenon of binocular luster can be evoked by simple dichoptic center-surround stimuli showing a luminance contrast difference between the eyes. Previous findings support the idea that this phenomenon is mediated by a low-level conflict mechanism that integrates the monocular signals from different types of contrast detector cells. Also, isoluminant stimuli with different chromatic contrasts between eyes can trigger sensations of luster. Here, we investigate whether the lustrous impression in such purely chromatic stimuli depends on interocular contrast differences and in particular on interocular contrast polarity pairings in a similar way as in the achromatic case. In our experiments, we measured the magnitude of the lustrous response using a series of isoluminant dichoptic center-ring-surround stimuli with varying ring width whose chromatic properties were varied along the red-green and blue-yellow cardinal directions. The trends in the data were very similar to those of our former study with achromatic stimuli, indicating similar mechanisms in both cases. The empirical luster data could also be predicted fairly well by a chromatic version of our interocular conflict model (with overall R2 values between 0.577 and 0.639), for which two different receptive field models were used, simulating the behavior of color-sensitive double-opponent cells in V1.

The Effect of Interocular Contrast Differences on the Appearance of Augmented Reality Imagery

Augmented reality (AR) devices seek to create compelling visual experiences that merge virtual imagery with the natural world. These devices often rely on wearable near-eye display systems that can optically overlay digital images to the left and right eyes of the user separately. Ideally, the two eyes should be shown images with minimal radiometric differences (e.g., the same overall luminance, contrast, and color in both eyes), but achieving this binocular equality can be challenging in wearable systems with stringent demands on weight and size. Basic vision research has shown that a spectrum of potentially detrimental perceptual effects can be elicited by imagery with radiometric differences between the eyes, but it is not clear whether and how these findings apply to the experience of modern AR devices. In this work, we first develop a testing paradigm for assessing multiple aspects of visual appearance at once, and characterize five key perceptual factors when participants viewed stimuli with interocular contrast differences. In a second experiment, we simulate optical see-through AR imagery using conventional desktop LCD monitors and use the same paradigm to evaluate the multi-faceted perceptual implications when the AR display luminance differs between the two eyes. We also include simulations of monocular AR systems (i.e., systems in which only one eye sees the displayed image). Our results suggest that interocular contrast differences can drive several potentially detrimental perceptual effects in binocular AR systems, such as binocular luster, rivalry, and spurious depth differences. In addition, monocular AR displays tend to have more artifacts than binocular displays with a large contrast difference in the two eyes. A better understanding of the range and likelihood of these perceptual phenomena can help inform design choices that support high-quality user experiences in AR.

Detection of vertical interocular phase disparities using luster as cue.

Interocular disparities in contrast generate an impression of binocular luster, providing a cue for their detection. Disparities in the carrier spatial phase of horizontally oriented Gabor patches also generate an impression of luster, so the question arises as to whether it is the disparities in local contrast that accompany the phase disparities that give rise to the luster. We examined this idea by comparing the detection of interocular spatial phase disparities with that of interocular contrast disparities in Gabor patches, in the latter case that differed in overall contrast rather than phase between the eyes. When bandwidth was held constant and Gabor spatial frequency was varied, the detection of phase and contrast disparities followed a similar pattern. However, when spatial frequency was fixed and Gabor envelope standard deviation (and hence number of modulation cycles) was varied, thresholds for detecting phase disparities followed a U-shaped function of Gabor standard deviation, whereas thresholds for contrast disparities, following an initial decline, were more-or-less constant as a function of Gabor standard deviation. After reviewing a number of possible explanations for the U-shape found with phase disparities, we suggest that the likely cause is binocular sensory fusion, the strength of which increases with the number of modulation cycles. Binocular sensory fusion would operate to reduce phase but not contrast disparities, thus selectively elevating phase disparity thresholds.

A simple model of binocular luster.

The dichoptic combination of simple center–surround stimuli showing a contrast difference between eyes can trigger a lustrous impression in the fused percept, particularly when the contrast polarities in the two input images are of opposite sign. Recent developments suggest that the phenomenon of binocular luster results from a neural conflict between ON and OFF visual pathways at an early binocular level. Support for this idea was found in a previous study in which the empirical luster judgments strongly correlated with the predictions of an interocular conflict model which was based on such ON–OFF pairings. However, our original model could not account for the fact that weaker lustrous sensations can also be evoked by stimuli showing contrast polarities of same sign between eyes. In the present study we present an improved model that also includes ON–ON and OFF–OFF pairings. The predictive power of this model was tested in a series of four experiments, using a total of about 500 different center–ring–surround configurations as test stimuli. We found that, overall, our modified version accounts for more than 80% of the variance in the empirical luster judgments and that the former problems could be largely resolved. Our results further suggest a nonlinear transducer function for the binocular conflict signals.

Binocular luster – A review

Binocular luster is a visual phenomenon that can be elicited by dichoptic stimuli showing an interocular difference in color or luminance contrast. For instance, when the two eyes are presented with simple center-surround stimuli in which the center patch in one eye is brighter and in the other eye darker than the common surround, the center patch in the fused percept assumes a lustrous appearance reminiscent of metal or graphite. Soon after the discovery of this phenomenon in the mid-19th century, it was intensively studied and several explanations were proposed. After this initial phase, however, research interest waned significantly. Stimulated by new insights into related phenomena and the underlying physiological mechanisms, the last 20 years have seen an increase in research activity in this field, which has considerably expanded our understanding of binocular luster. In this paper, we provide a detailed review of research on binocular luster over the past 170 years. We present and discuss the existing findings in a number of separate sections, dealing with 1) the phenomenology of binocular luster, 2) different theories that have been proposed, 3) several factors influencing the lustrous impression, 4) the relationship between binocular luster and binocular rivalry, 5) the current understanding of its neural basis, and 6) potential applications based on binocular luster.

On the Art of Binocular Rivalry.

Binocular rivalry has a longer descriptive history than stereoscopic depth perception both of which were transformed by Wheatstone's invention of the stereoscope. Thereafter, artistic interest in binocular vision has been largely confined to stereopsis. A brief survey of research on binocular contour rivalry is followed by anaglyphic examples of its expression as art. Rivalling patterns can be photographs, graphics, and combinations of them. In addition, illustrations of binocular lustre and interactions between rivalry and stereopsis are presented, as are rivalling portraits of some pioneers of the science and art of binocular vision. The question of why a dynamic process like binocular rivalry has been neglected in visual art is addressed.

On the Origins of Terms in Binocular Vision.

Vision with two eyes has been commented upon for many centuries, and the principal concern has been with binocular single vision. The terminology we apply to binocular vision developed rapidly after the invention of the stereoscope in the early 19th century. The origins of terms such as anaglyph, binocular lustre, chromatic stereoscope, cyclopean eye, dichoptic, horopter, pseudoscope, rivalry, stereoscope, stereograph, and stereopsis are described together with portraits of those who introduced them.

Binocular Lustre: Does identification of interocular contrast difference require opposite (light-dark) contrasts in the two eyes?

Binocular Lustre: Does identification of interocular contrast difference require opposite (light-dark) contrasts in the two eyes?

The role of contrast polarities in binocular luster: Low-level and high-level processes

The binocular fusion of two center-surround configurations, where one center is brighter, the other darker than the common surround, leads to a strong impression of luster in the central patch. Without reversed contrast polarities of the center patches, this impression is much weaker or even absent. However, we observed that in the latter case the perceived luster can be considerably enhanced by enclosing both centers with a thin ring of fixed luminance. Compared to the standard stimulus, this center-ring-surround configuration shows much less binocular rivalry and the luster has also a different, more glass-like material quality. In a psychophysical experiment, we examined how the magnitude of the lustrous response depends on the width of the ring, both in stimuli with reversed and consistent contrast polarities. It has been proposed that binocular luster results from a neuronal conflict between ON and OFF visual pathways. To test this hypothesis with respect to our data, we developed a simple model to estimate the amount of interocular conflict resulting from a given binocular stimulus pair and applied it to all stimuli used in the experiment. We found strong correlations between the interocular conflict measure and the strength of luster observed in the experiment, suggesting that a common low-level mechanism determines the magnitude of the lustrous response. Regarding the differences in the perceived material quality of the lustrous impressions, we discuss evidence indicating that high-level processes are involved that promote the visual system’s interpretation of the ring-stimuli as a certain depth-segmented 3D scene.

At least two distinct mechanisms control binocular luster, rivalry, and perceived rotation with contrast and average luminance disparities.

When one views a square-wave grating and dichoptically changes the average luminance or contrast of the monocular images, at least three perceptual phenomena might occur. These are the Venetian blind effect, or a perceived rotation of the bars around individual vertical axes; binocular luster, or a perceived shimmering; and binocular rivalry, or an alternating perception between the views of the two eyes. Perception of luster and rivalry occur when the "light bars" in the grating dichoptically straddle the background luminance (one eye’s image has a higher luminance than the background and the other eye’s image has a lower luminance than the background), with little impact from the "dark bars." Perception of rotation, on the other hand, is related to average luminance or contrast disparity, independent of whether or not the "light bars" straddle the background luminance. The patterns for perceived rotation versus binocular luster and binocular rivalry suggest at least two separate mechanisms in the visual system for processing luminance and contrast information over and above their differing physiological states suggested by their different appearances. While luster and rivalry depend directly on the relation between stimuli and the background, perceived rotation depends on the magnitude of the luminance or contrast disparity, as described by the generalized difference model.

Binocularity and visual search-Revisited.

Binocular rivalry is a phenomenon of visual competition in which perception alternates between two monocular images. When two eye's images only differ in luminance, observers may perceive shininess, a form of rivalry called binocular luster. Does dichoptic information guide attention in visual search? Wolfe and Franzel (Perception & Psychophysics, 44(1), 81-93, 1988) reported that rivalry could guide attention only weakly, but that luster (shininess) "popped out," producing very shallow Reaction Time (RT) × Set Size functions. In this study, we have revisited the topic with new and improved stimuli. By using a checkerboard pattern in rivalry experiments, we found that search for rivalry can be more efficient (16 ms/item) than standard, rivalrous grating (30 ms/item). The checkerboard may reduce distracting orientation signals that masked the salience of rivalry between simple orthogonal gratings. Lustrous stimuli did not pop out when potential contrast and luminance artifacts were reduced. However, search efficiency was substantially improved when luster was added to the search target. Both rivalry and luster tasks can produce search asymmetries, as is characteristic of guiding features in search. These results suggest that interocular differences that produce rivalry or luster can guide attention, but these effects are relatively weak and can be hidden by other features like luminance and orientation in visual search tasks.

Binocularity and Visual Search – Revisited

Binocular rivalry is a phenomenon of visual competition in which perception alternates between two monocular images. When two eye’s images only differ in luminance, observers may perceive shininess, a form of rivalry called binocular luster. Does dichoptic information guide attention in visual search? Wolfe and Franzel (Perception & Psychophysics, 44(1), 81–93, 1988) reported that rivalry could guide attention only weakly, but that luster (shininess) “popped out,” producing very shallow Reaction Time (RT) × Set Size functions. In this study, we have revisited the topic with new and improved stimuli. By using a checkerboard pattern in rivalry experiments, we found that search for rivalry can be more efficient (16 ms/item) than standard, rivalrous grating (30 ms/item). The checkerboard may reduce distracting orientation signals that masked the salience of rivalry between simple orthogonal gratings. Lustrous stimuli did not pop out when potential contrast and luminance artifacts were reduced. However, search efficiency was substantially improved when luster was added to the search target. Both rivalry and luster tasks can produce search asymmetries, as is characteristic of guiding features in search. These results suggest that interocular differences that produce rivalry or luster can guide attention, but these effects are relatively weak and can be hidden by other features like luminance and orientation in visual search tasks.

ColorBless

Binocular disparity allows interesting visual effects visible only to people with stereoscopic 3D displays. Here, we studied and applied one such effect, binocular luster, to the application of digital colorblind aids with active shutter 3D. We developed two prototype techniques, ColorBless and PatternBless, to investigate the effectiveness of such aids and to explore the potential applications of a luster effect in stereoscopic 3D beyond highlighting. User studies and interviews revealed that luster-based aids were fast and required lower cognitive effort than existing aids and were preferred over other aids by the majority of colorblind participants. We infer design implications of a luster effect from the study and propose potential applications in augmented visualization.

Lustrous material appearances: Internal and external constraints on triggering conditions for binocular lustre.

Lustrous surface appearances can be elicited by simple image configurations with no texture or specular highlights, as most prominently illustrated by Helmholtz' demonstration of stereoscopic lustre. Three types of explanatory framework have been proposed for stereoscopic lustre, which attribute the phenomenon to a binocular luminance conflict, an internalised physical regularity (Helmholtz), or to a disentangling of “essential” and “accidental” attributes in surface representations (Hering). In order to investigate these frameworks, we used haploscopically fused half-images of centre-surround configurations in which the luminances of the test patch were dynamically modulated. Experiment 1 shows that stereoscopic lustre is not specifically tied to situations of a luminance conflict between the eyes. Experiment 2 identifies a novel aspect in the binocular temporal dynamics that provides a physical basis for lustrous appearances, namely the occurrence of a temporal luminance counter-modulation between the eyes. This feature sheds some light on the internal principles underlying a disentangling of “accidental” and “essential” surface attributes. Experiment 3 reveals an asymmetry between a light and a dark reference level for the counter-modulations. This finding again suggests an interpretation in terms of an internalised physical regularity with respect to the dynamics of perceiving illuminated surfaces.

Alternation Frequency Thresholds for Stereopsis as a Technique for Exploring Stereoscopic Difficulties

When stereoscopic images are presented alternately to the two eyes, stereopsis occurs at F ≥ 1 Hz full-cycle frequencies for very simple stimuli, and F ≥ 3 Hz full-cycle frequencies for random-dot stereograms (eg Ludwig I, Pieper W, Lachnit H, 2007 “Temporal integration of monocular images separated in time: stereopsis, stereoacuity, and binocular luster” Perception & Psychophysics 69 92–102). Using twenty different stereograms presented through liquid crystal shutters, we studied the transition to stereopsis with fifteen subjects. The onset of stereopsis was observed during a stepwise increase of the alternation frequency, and its disappearance was observed during a stepwise decrease in frequency. The lowest F values (around 2.5 Hz) were observed with stimuli involving two to four simple disjoint elements (circles, arcs, rectangles). Higher F values were needed for stimuli containing slanted elements or curved surfaces (about 1 Hz increment), overlapping elements at two different depths (about 2.5 Hz increment), or camouflaged overlapping surfaces (> 7 Hz increment). A textured cylindrical surface with a horizontal axis appeared easier to interpret (5.7 Hz) than a pair of slanted segments separated in depth but forming a cross in projection (8 Hz). Training effects were minimal, and F usually increased as disparities were reduced. The hierarchy of difficulties revealed in the study may shed light on various problems that the brain needs to solve during stereoscopic interpretation. During the construction of the three-dimensional percept, the loss of information due to natural decay of the stimuli traces must be compensated by refreshes of visual input. In the discussion an attempt is made to link our results with recent advances in the comprehension of visual scene memory.

Perceived Depth in the ‘Sieve Effect’ and Exclusive Binocular Rivalry

An impression of a surface seen through holes is created when one fuses dichoptic pairs of discs, with one member of each pair black and the other member white. This is referred to as the 'sieve effect'. The stimulus contains no positional disparities. Howard (1995, Perception 24 67-74) noted qualitatively that the sieve effect occurs when the rivalrous regions are within the range of sizes, contrasts, and relative sizes where exclusive rivalry occurs, rather than binocular lustre, stimulus combination, or dominant rivalry. This suggests that perceived depth in the sieve effect should be at a maximum when exclusive rivalry is most prominent. We used a disparity depth probe to measure the magnitude of perceived depth in the sieve effect as a function of the sizes, contrasts, and relative sizes of the rivalrous regions. We also measured the rate of exclusive rivalry of the same stimuli under the same conditions. Perceived depth and the rate of exclusive rivalry were affected in the same way by each of the three variables. Furthermore, perceived depth and the rate of exclusive rivalry were affected in the same way by changes in vergence angle, although the configuration of the stimulus surface was held constant. These findings confirm the hypothesis that the sieve effect is correlated with the incidence of exclusive rivalry.

Temporal integration of monocular images separated in time: Stereopsis, stereoacuity, and binocular luster

We evaluated stereopsis and binocular luster using electronically controlled shutter glasses with alternating monocular stimulation. In Experiment 1, we used the standard method for testing stereoacuity to obtain a gradual measure of stereopsis. Stereo thresholds decreased with increasing alternating frequency of two monocular half-images without a delay between them. Increasing delays led to increasing thresholds. In Experiment 2, we compared stereopsis resulting from two monocular half-images of a random-dot stereogram and binocular luster with respect to the minimum alternating frequency of the two half-images and the maximum interocular delay that were tolerated without a breakdown of the impression. Below 3 Hz, no stereopsis occurred. Binocular luster was observed only above 10 Hz. The mean threshold of interocular delay for detecting the global figure in a random-dot stereogram was about 51 msec, but for binocular luster it was about 20 msec. Overall, temporal integration was better for stereopsis than for binocular luster.

Observation and measurement of the appearance of metallic materials. Part I. Macro appearance

Part I of this article dealt with the appearance of metallic materials observed at a distance of a few meters. This part deals with the appearance at reading distance. Metallic materials exhibit various appearance attributes, including glitter, glints, depth, coherence glitter, binocular luster, binocular glitter, and binocular mottle. Color disparity is proposed as a measure of binocular luster. Metallic materials resemble grainy photographs, so the method used in photography to quantify graininess by measuring blending distance is introduced. Objective measures of granularity are proposed as correlates of graininess. The term “subsurface” is applied to the apparent “surface” lying beneath the glossy surface. Methods of optical image analysis, such as point spread function, edge spread function, Wiener spectrum, modulation transfer function, and image correlation are proposed to characterize the appearance of metallic surfaces. Polarization and cylindrical presentation may aid measurements. Binocular attributes of appearance introduced here require analysis of the disparity between two points of view. New kinds of pigments may require new methods of measurement. © 1998 John Wiley & Sons, Inc. Col Res Appl, 23: 362–373, 1998

Depth from Binocular Rivalry without Spatial Disparity

Some new stereoscopic effects are reported that arise from dichoptic stimuli containing no binocular disparity. In one effect, identical arrays of small black discs are presented to the two eyes and slightly smaller white discs are superimposed on one of each pair of black discs. This creates the impression of a surface with holes in it, through which is seen a surface with fluctuating black and white areas. This is referred to as the 'sieve effect'. The white discs must subtend less than about 1 deg of visual angle. With larger discs the black and white areas no longer exhibit alternating rivalry but combine to produce binocular lustre. This destroys the sieve effect. The sieve effect is weak or nonexistent when the black and white discs are the same size, showing that well-defined binocular rims are required for the effect. When the monocular white discs are reduced to dots, the impression of a surface seen through holes gives way to the impression of an array of dots behind or standing out from the background. In this case the monocular dots permanently dominate the homogeneous backgrounds in the other eye and the impression of depth can be explained in terms of apparent parallax or of disparity due to the instability of vergence.

Seeing depth in colour: More than just what meets the eyes

Novel binocular depth illusions obtained from two-dimensional colour images are presented. It is demonstrated that the magnitude of these illusions is based on transverse chromatic aberation (TCA), however, the depth obtained cannot be observed unless specific conditions are met even if the TCA is present. Some form of perceptual organization occurring at and/or beyond the binocular fusion site of the brain, is required for some of these effects to occur. An example of a paradoxical finding leading to this conclusion is the observation that under some conditions the same colour can be perceived on separate depth planes while spatially adjacent colours from opposing ends of the visible spectrum (i.e. red and blue or green) can be perceived on the same depth plane simultaneously within the same image. Further, results show that some form of reference plane is required by the brain to use the colour induced disparity, without which, depth cannot be perceived even if the disparity information is present. This phenomenon is spatially tuned for medium to high frequency components and is still detectable under isoluminant conditions which would support the notion that it requires information from the parvocellular pathway. Binocular lustre and rivaldepth are ruled out as being significant factors in the effect. It is argued that this phenomenon represents an instance of global interactive processes induced by TCA while previous studies on chromostereopsis have concentrated on local aspects. Results of the present study may explain why under certain situations depth can be perceived in coloured images and not under other circumstances where TCA is still present.