Binocular Luminance Research Articles

Effects of binocular disparity on binocular luminance combination.

This study aimed to examine the effects of binocular disparity on binocular combination of brightness information coming from luminance increments and decrements. The point of subjective equality was determined by asking the observers to judge which stimulus appeared brighter-a bar stimulus with variable disparity or another stimulus with zero disparity. For the bar stimulus, the interocular luminance ratio was varied to trace an equal brightness curve. Binocular disparity had no effect on luminance increments presented on a gray or black background. In contrast, when luminance decrements were presented on a gray background, non-zero disparities elevated points of subjective equality for stimuli with interocular luminance differences. This means that the binocular brightness combination of the two monocular signals shifted from winner-take-all summation toward linear averaging. It has been argued that this effect may be caused by non-zero binocular disparities attenuating interocular suppression, which is deemed to operate normally with zero disparity.

Poster Session II: SSVEP measurements of color and spatial frequency response in V1.

Recent work from our group (Segala et al, eLife, 2023) shows that the rules for binocular luminance signal combination depend on spatial frequency (SF). Structured patterns show strong interocular suppression while unstructured inputs (mean field disks) do not. Here, we used SSVEPs to ask if SF dependence is also found in chromatic pathways. SSVEPs were recorded from 12 subjects using a canonical V1 template (Poncet & Ales, 2023). Eyes were targeted using shutter goggles and stimuli were contrast-reversing gratings or disks at 5Hz (left eye) and 7Hz (right eye). Experimental factors were stimulus SF (disk, grating 1cpd), chromaticity (LMS, L-M or S-cone isolating) and ocularity (left, right or both). Monocular conditions generated large responses at 2F. In binocular conditions, all 2F responses showed suppression, and significant intermodulation (IM) terms (sums and differences of the inputs - e.g., 2Hz) were present. The magnitude of both suppression and IM in the binocular condition depended on SF and chromaticity; IM amplitudes were higher for gratings compared to disks in the luminance condition, but higher for disks compared to gratings in the chromatic conditions. Overall we found significant differences in the spectral response signatures across all stimulus combinations. All inputs undergo binocular combination in V1 but the rules governing the combination appear to depend on both chromaticity and SF.

Capturing Luminous Flux Entering Human Eyes with a Camera, Part 2: A Field Verification Experiment

ABSTRACT A space occupant’s real-time exposure to light reaching his/her eyes has been a concern in lighting research and design practice. Following the parallel fundamental research in Part 1, Part 2 of this study explored a way to use a Canon 550D fitted with the Sigma 4.5 mm F2.8 circular fisheye lens to estimate the luminous flux arriving at the entrance pupil from the visible luminous environment. By taking two 180° HDR images at the same camera position but in different aiming directions and merging them into a single luminance map covering the observer’s entire binocular visual field (214° horizontally and 125° vertically), the monocular and binocular luminance map can be generated with the aid of the dynamic visual field model proposed in Part 1. In a field verification experiment, the luminous flux passing through the entrance pupil in the preset scenes and gaze angles was estimated. Individual luminous contribution from an object or a region of interest within the occupant’s dynamic binocular visual field or subfields was also calculated. This study expanded the capacity of HDR photography in lighting measurement to capture binocular luminous flux entering human eyes as input for optimizing human-light interaction in various luminous environments.

Binocular combination of luminance profiles.

We develop and test a new two-dimensional model for binocular combination of the two eyes' luminance profiles. For first-order stimuli, the model assumes that one eye's luminance profile first goes through a luminance compressor, receives gain-control and gain-enhancement from the other eye, and then linearly combines the other eye's output profile. For second-order stimuli, rectification is added in the signal path of the model before the binocular combination site. Both the total contrast and luminance energies, weighted sums over both the space and spatial-frequency domains, were used in the interocular gain-control, while only the total contrast energy was used in the interocular gain-enhancement. To challenge the model, we performed a binocular brightness matching experiment over a large range of background and target luminances. The target stimulus was a dichoptic disc with a sharp edge that has an increment or decrement luminance from its background. The disk's interocular luminance ratio varied from trial to trial. To refine the model we tested three luminance compressors, five nested binocular combination models (including the Ding–Sperling and the DSKL models), and examined the presence or absence of total luminance energy in the model. We found that (1) installing a luminance compressor, either a logarithmic luminance function or luminance gain-control, (2) including both contrast and luminance energies, and (3) adding interocular gain-enhancement (the DSKL model) to a combined model significantly improved its performance. The combined model provides a systematic account of binocular luminance summation over a large range of luminance input levels. It gives a unified explanation of Fechner's paradox observed on a dark background, and a winner-take-all phenomenon observed on a light background. To further test the model, we conducted two additional experiments: luminance summation of discs with asymmetric contour information (Experiment 2), similar to Levelt (1965) and binocular combination of second-order contrast-modulated gratings (Experiment 3). We used the model obtained in Experiment 1 to predict the results of Experiments 2 and 3 and the results of our previous studies. Model simulations further refined the contrast space weight and contrast sensitivity functions that are installed in the model, and provide a reasonable account for rebalancing of imbalanced binocular vision by reducing the mean luminance in the dominant eye.

Detection of between-eye differences in color: Interactions with luminance.

Between-eye differences in color or luminance result in the appearance of luster, which provides a cue for detecting between-eye differences. We measured thresholds for detecting between-eye differences in both hue and chromatic contrast (saturation) in dichoptically superimposed color patches. Sensitivity was found to be highest at isoluminance and decreased with the addition of task-irrelevant, spatially coextensive, binocular (i.e., same in both eyes) luminance contrast. However, when the members of each dichoptic pair were presented side by side on the screen and viewed with the same eye, the added luminance contrast had no effect on the detection of their differences. If the effect of the luminance contrast was simply to dilute or desaturate the chromatic signals, we would expect thresholds to increase for the within-eye and not just the between-eye (dichoptic) conditions. We suggest that the presence of binocular luminance contrast reduces the interocular suppression between the dichoptic colors, causing the dichoptic color pairs to blend, thus rendering their differences harder to detect.

Dichoptic colour-saturation masking is unmasked by binocular luminance contrast

We demonstrate a new type of interaction between suprathreshold colour (chromatic) and luminance contrast in the context of binocular, specifically dichoptic vision. A highly saturated isoluminant violet ‘mask’ disk in one eye greatly elevates detection thresholds for an isoluminant violet ‘test’ disk in the other eye, an example of dichoptic colour-saturation masking. However when binocular luminance contrast (i.e. luminance contrast matched in the two eyes) is added to the disks, the masking is dramatically reduced. Adding binocular luminance contrast to the test disk on its own, or to the mask and test disks presented together in both eyes had comparatively little effect on test thresholds. The likely explanation for the dichoptic unmasking effect is that the binocular luminance contrast reduced the interocular suppression between chromatic mask and test, in keeping with other recent findings from measurements of the appearance of dichoptic saturation mixtures (Kingdom & Libenson, 2015). We suggest that binocularly matched luminance contrast promotes the interpretation that the dichoptic colour saturations, even though unmatched, nevertheless originate from a single object. Under these conditions the visual system tends to blend the mask and test saturations rather than have them compete, resulting in reduced dichoptic masking. We term this idea the “object commonality” hypothesis.

Interocular contrast gain control plus monocular luminance gain control can explain binocular luminance summation

Interocular contrast gain control plus monocular luminance gain control can explain binocular luminance summation

Relative roles of luminance and fixation in inducing dissociated vertical divergence.

We evaluated the roles of luminance and fixation in the pathophysiology of dissociated vertical divergence (DVD). Vertical eye position was measured in 6 subjects with DVD (ages 11-47 years, 5 females) and 6 controls (ages 16-40 years, 5 females) using video-oculography (VOG) under conditions of change in fixation and luminance. Subjects with DVD showed the following VOG responses. When fixation was precluded with a translucent filter and bright light was shone into one eye to produce a marked binocular luminance disparity, we found some subjects had a small induced vertical divergence causing the illuminated eye to be lower than the nonilluminated eye (mean -1.6° ± 1.5°, P = 0.06 compared to no vertical divergence using the signed rank test). When fixation was precluded with a translucent filter, while alternate occlusion produced a mild binocular luminance disparity, we found a smaller vertical divergence of the eyes that was not statistically significant (1.2° ± 2.1°, P = 0.3). When alternate occlusion produced reversal of monocular fixation in the dark (with essentially no change in peripheral luminance disparity), there was a significant vertical divergence movement causing the covered eye to be relatively higher than the uncovered eye (7.2° ± 3.1°, P = 0.03). The amplitude of this vertical divergence was similar to that measured under conditions of alternate occlusion in a lighted room (where there also was a significant average relative upward movement of the covered eye of 8.1° ± 2.9°, P = 0.03). Control subjects showed no vertical divergence under any testing conditions. Dissociated vertical divergence is mediated primarily by changes in fixation and only to a minor degree by binocular luminance disparity.

Binocular luminance contrast reduces dichoptic masking between chromatic stimuli

Binocular luminance contrast reduces dichoptic masking between chromatic stimuli

Investigation of Designated Eye Position and Viewing Zone for a two-view autostereoscopic display

Designated eye position (DEP) and viewing zone (VZ) are important optical parameters for designing a two-view autostereoscopic display. Although much research has been done to date, little empirical evidence has been found to establish a direct relationship between design and measurement. More rigorous studies and verifications to investigate DEP and to ascertain the VZ criterion will be valuable. We propose evaluation metrics based on equivalent luminance (EL) and binocular luminance (BL) to figure out DEP and VZ for a two-view autostereoscopic display. Simulation and experimental results prove that our proposed evaluation metrics can be used to find the DEP and VZ accurately.

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.

Perceived Suprathreshold Depth Under Conditions that Elevate the Stereothreshold

Previous studies considered the possibility that individuals with impaired stereoacuity can be identified by estimating the perceived depth of a target with a suprathreshold retinal image disparity. These studies showed that perceived suprathreshold depth is reduced when the image presented to one eye is blurred, but they did not address whether a similar reduction of perceived depth occurs when the stereothreshold is elevated using other manipulations. Stereothresholds were measured in six adult observers for a pair of bright 1-degree vertical lines during normal viewing and under five conditions that elevated the stereothreshold: monocular dioptric blur, monocular glare, binocular luminance reduction, monocular luminance reduction, and imposed disjunctive image motion. The observers subsequently matched the perceived depth of degraded targets presented with crossed or uncrossed disparities corresponding to two, four, and six times the elevated stereothreshold for each stimulus condition. The image manipulations used elevated the stereothreshold by a factor of 3.7 to 5.5 times. For targets with suprathreshold disparities, monocular blur, monocular luminance reduction, and disjunctive image motion resulted in a significant decrease in perceived depth. However, the magnitude of perceived suprathreshold depth was unaffected when monocular glare was introduced or the binocular luminance of the stereotargets was reduced. Not all conditions that increase the stereothreshold reduce the perceived depth of targets with suprathreshold disparities. Observers who have poor stereopsis therefore may or may not exhibit an associated reduction of perceived suprathreshold depth.

The psychophysics of detecting binocular discrepancies of luminance

In the natural world, a binocular discrepancy of luminance can signal a glossy surface. Using a spatial forced choice task, we have measured the ability of subjects to detect binocular luminance disparities. We show that the detection of binocular luminance disparity shares several basic psychophysical features with the detection of surface properties such as lightness and chromaticity: an approximation to Weber’s Law, spatial summation, temporal summation, and a deterioration with increasing eccentricity. We also discuss whether color-deficient subjects could derive reliable information about chromaticity from the binocular disparities of luminance induced by a monocularly worn color filter.

Colour–luminance interactions in binocular summation

Using a noise-masking paradigm we test the notion of binocular detection mechanisms that combine luminance and colour contrast. Binocular summation was measured for achromatic and red-green isoluminant Gabor stimuli over a range of temporal frequencies and was compared with and without the presence of a two-dimensional, dynamic, luminance noise mask (correlated). While we found that luminance noise reduced binocular luminance summation at all temporal frequencies, binocular red-green summation was reduced only at frequencies of 8 Hz and above. Our results suggest the existence of binocular colour–luminance interactions restricted to high temporal frequencies.

Functional and structural abnormalities in the visual cortex in early childhood strabismus

To investigate the structural basis for functional deficits in infantile strabismus we used a neuroanatomic tracer and a histochemical label to examine the primary visual cortex (area V1) of adult esotropic macaque monkeys. The animals had developed natural esotropia in the first months of life, alternated fixation, and exhibited the ocular motor signs that typify strabismus with onset in infancy. After behavioral and VEP testing, ocular dominance columns (ODCs) in V1 were injected with a neuronal traser and labeled for cytochrome oxidase activity. The strabismic monkeys showed striking deficits in binocular luminance visually-evoked potentials (VEPs) and characteristic directional asymmetries in motion VEPs. Binocular horizontal connections between ODCs were reduced an average of 50-60% in strabismic as compared to normal monkeys. ODCs also showed unequal metabolic activity with contralaterally (i.e. nasal retina) driven ODCs showing greater activity in each V1. The maldevelopment of connections in upper V1 layers correlates with the abnormalities in binocular and motion VEPs. The unequal metabolic activity suggests interocular suppression. These results provide the first neuroanatomic evidence for cerebral cortex maldevelopments in natural infantile esotropia.

Stereopsis due to luminance differences in the two eyes

A local region in an image is seen as slanted when the two eyes are shown different luminance values in that region. The steepness of the slant depends upon the size of the region and the difference in the luminance values in the two eyes. Three examples where this phenomenon influences depth perception are given: (1) stereopsis without corresponding binocular luminance edges is shown to be a limiting case of the phenomenon; (2) edges less than 1 min arc apart can be seen in relative depth with respect to each other; and (3) regions that appear transparent or translucent can be seen in depth despite having all the luminance edges at zero disparity in simple stereo images.

New phenomena linking depth and luminance in stereoscopic motion

A novel random-dot stereogram (RDS) was used to study stereoscopic motion. For this RDS stimulus, the direction of luminance motion and the direction of the moving cyclopean pattern can be independently controlled. The perceived cyclopean motion was examined under five different conditions, in which the cyclopean pattern was moving either up or down, the luminant dots were: (1) moving in the cyclopean direction; (2) moving opposite to the cyclopean direction; (3) moving orthogonal to the cyclopean direction, (4) stationary; or (5) dynamic (dots uncorrelated in successive frames). The study showed that luminance direction dominated cyclopean direction and that smooth and coherent cyclopean motion is seen only if luminance motion is present. The results suggest that stereoscopic motion is processed by interactions between separate binocular disparity units and luminance motion units, and not by a single binocular motion system, in which binocular units are tuned to both disparity and direction of motion.

Binocular luminance summation (BLS) in esotropic and exotropic kittens.

Binocular luminance summation (BLS) in esotropic and exotropic kittens.

Functional and neuronal binocularity in kittens raised with rapidly alternating monocular occlusion.

1. In order to determine the degree of synchrony of binocular activation required for the development of binocularity we reared 11 kittens with rapidly alternating monocular occlusion. Alternating occlusion was achieved with microprocessor-controlled electrooptic solid-state shutters, which were fitted to individually moulded goggles. The intervals of alternating occlusion were varied from 50 to 1,000 ms. Two normally reared kittens and three kittens that were reared with the shutters operating synchronously with open/close intervals of 50/50 ms, 200/200 ms, and 400/100 ms, respectively, were used as controls. Toward the end of the critical period we examined the kittens' ability for binocular depth discrimination and tested binocular luminance summation of the pupillary light reflex. Single-cell recordings were made from the visual cortex in order to determine the percentages of binocularly excitable neurons. 2. There was a good correlation between the degree of asynchrony of binocular experience, the impairment of depth discrimination, and the percentage of binocular neurons. Kittens reared with alternation rates of 200, 330, and 400 ms, respectively, had developed normal binocularity and were indistinguishable from the controls. Alternation rates of 500 ms or longer prevented the development of normal depth discrimination and luminance summation and resulted in reduced cortical binocularity. 3. A linear relationship between depth discrimination, binocular luminance summation, and percentages of binocular neurons was found. 4. Our findings indicate that an asynchrony of binocular activation of several hundred milliseconds is compatible with the development of normal binocularity in the kitten visual system.

Binocular Luminance Summation in Infants

The difference in pupil diameter between monocular and binocular viewing conditions has been found to be significantly different in human infants at an age of onset that is positively correlated with the age of onset for stereopsis. We attempted to use this information on binocular luminance summation (BLS) to devise a simple objective test using a direct ophthalmoscope in a modified two-part swinging-flashlight test. We evaluated 67 subjects with varying degrees of known heterotropia ranging in age from 16 hours to 20 years in an effort to determine a threshold measure of stereo-acuity or degree of heterotropia at which the test result might reproducibly change. We found BLS to be normally absent until about 4 months of age. All subjects older than 4 months manifested summation regardless of the extent of heterotropia, thus making our test unusable. We conclude that BLS is more than an ipsilateral consensual pupillary response, and we concur with others that these visual pathways must undergo maturation beyond the time of birth.