Binocular luster - A review

Predicted effectiveness of EnChroma multi-notch filters for enhancing color perception in anomalous trichromats

EnChroma filters are aids designed to improve color vision for anomalous trichromats. Their use is controversial because the results of lab-based assessments of their effectiveness have so far largely failed to agree with positive anecdotal reports. However, the effectiveness of EnChroma filters will vary depending on the conditions of viewing, including whether the stimuli are broadband reflective surfaces or colors presented on RGB displays, whether illumination spectra are broadband or narrowband, the transmission spectra of particular filters, and the cone spectral sensitivity functions of the observer. We created a model of anomalous trichromatic color vision to predict the effects of EnChroma filters on the color signals impaired in anomalous trichromacy. Using the model we varied illumination, filter type and observer cone sensitivity functions, and tested the effect of presenting colors as broadband reflective surfaces or on RGB displays. We also used hyperspectral images to assess the impact of the filters on anomalous trichromats' color vision for natural scenes. Model results predicted that the filters should be broadly effective at enhancing anomalous trichromats' equivalent to L/(L + M) chromatic contrasts under a range of viewing conditions, but are substantially more effective for deuteranomals than for protanomals. The filters are predicted to be more effective for broadband reflective surfaces presented under broadband illuminants than for surfaces presented under narrowband illuminants or for colors presented on RGB displays. Since the potential impacts of contrast adaptation and perceptual learning are not considered in the model, it needs to be empirically validated. Results of empirical tests of the effects of EnChroma filters on deuteranomalous color vision in comparison with model predictions are presented in an accompanying paper (Somers et al., in prep.).

Peripheral vision is mainly for looking rather than seeing

Vision includes looking and seeing. Looking, mainly via gaze shifts, selects a fraction of visual input information for passage through the brain's information bottleneck. The selected input is placed within the attentional spotlight, typically in the central visual field. Seeing decodes, i.e., recognizes and discriminates, the selected inputs. Hence, peripheral vision should be mainly devoted to looking, in particular, deciding where to shift the gaze. Looking is often guided exogenously by a saliency map created by the primary visual cortex (V1), and can be effective with no seeing and limited awareness. In seeing, peripheral vision not only suffers from poor spatial resolution, but is also subject to crowding and is more vulnerable to illusions by misleading, ambiguous, and impoverished visual inputs. Central vision, mainly for seeing, enjoys the top-down feedback that aids seeing in light of the bottleneck which is hypothesized to starts from V1 to higher areas. This feedback queries for additional information from lower visual cortical areas such as V1 for ongoing recognition. Peripheral vision is deficient in this feedback according to the Central-peripheral Dichotomy (CPD) theory. The saccades engendered by peripheral vision allows looking to combine with seeing to give human observers the impression of seeing the whole scene clearly despite inattentional blindness.

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.

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.

The Perceptual Science of Augmented Reality

Augmented reality (AR) systems aim to alter our view of the world and enable us to see things that are not actually there. The resulting discrepancy between perception and reality can create compelling entertainment and can support innovative approaches to education, guidance, and assistive tools. However, building an AR system that effectively integrates with our natural visual experience is hard. AR systems often suffer from visual limitations and artifacts, and addressing these flaws requires basic knowledge of perception. At the same time, AR system development can serve as a catalyst that drives innovative new research in perceptual science. This review describes recent perceptual research pertinent to and driven by modern AR systems, with the goal of highlighting thought-provoking areas of inquiry and open questions.

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.