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Previous research has demonstrated the existence of the face race lightness (FRL) illusion. It indicates that Black faces tend to appear darker than White faces, even when their luminance values are objectively adjusted to be the same. However, the debate over the exclusive influence of face-race categories on the FRL illusion continues, with the impact of racial groups on the illusion remaining relatively unexplored. To address these gaps, we conducted studies to investigate whether the FRL illusion varies in terms of racial salience and racial groups. We manipulated the racial salience by altering the orientation of the faces. A total of 64 Caucasians (Study 1) and 63 Asians (Study 2) were recruited. Participants were shown pairs of faces in rapid succession and were asked to report which face appeared lighter or darker. In each trial, the two faces belonged to the same race category: Black, Black–White ambiguous, or White. The luminance of the first face remained consistent across trials while the luminance of the second face varied and was adjusted across eight levels (− 20, − 12, − 8, − 4, + 4, + 8, + 12, + 20). Our findings reveal that the FRL illusion is largely dependent on the salience of face-race information. When faces were presented upright, the FRL illusion was prominent; however, it disappeared when faces were inverted. Remarkably, the FRL illusion was observed not only in Caucasians but also in Asians. Therefore, our results suggest that the FRL illusion primarily stems from race salience rather than participants' racial groups. [ABSTRACT FROM AUTHOR]

Head-mounted displays (HMDs) are becoming more and more popular as a device for displaying a virtual reality space, but how real are they? The present study attempted to quantitatively evaluate the degree of reality achieved with HMDs by using a perceptual phenomenon as a measure. Lightness constancy is an ability that is present in human visual perception, in which the perceived reflectance (i.e., the lightness) of objects appears to stay constant across illuminant changes. Studies on color/lightness constancy in humans have shown that the degree of constancy is high, in general, when real objects are used as stimuli. We asked participants to make lightness matches between two virtual environments with different illuminant intensities, as presented in an HMD. The participants' matches showed a high degree of lightness constancy in the HMD; our results marked no less than 74.2% (84.8% at the maximum) in terms of the constancy index, whereas the average score on the computer screen was around 65%. The effect of head-tracking ability was confirmed by disabling that function, and the result showed a significant drop in the constancy index but that it was equally effective when the virtual environment was generated by replay motions. HMDs yield a realistic environment, with the extension of the visual scene being accompanied by head motions. [ABSTRACT FROM AUTHOR]

Head-mounted displays (HMDs) are becoming more and more popular as a device for displaying a virtual reality space, but how real are they? The present study attempted to quantitatively evaluate the degree of reality achieved with HMDs by using a perceptual phenomenon as a measure. Lightness constancy is an ability that is present in human visual perception, in which the perceived reflectance (i.e., the lightness) of objects appears to stay constant across illuminant changes. Studies on color/lightness constancy in humans have shown that the degree of constancy is high, in general, when real objects are used as stimuli. We asked participants to make lightness matches between two virtual environments with different illuminant intensities, as presented in an HMD. The participants’ matches showed a high degree of lightness constancy in the HMD; our results marked no less than 74.2% (84.8% at the maximum) in terms of the constancy index, whereas the average score on the computer screen was around 65%. The effect of head-tracking ability was confirmed by disabling that function, and the result showed a significant drop in the constancy index but that it was equally effective when the virtual environment was generated by replay motions. HMDs yield a realistic environment, with the extension of the visual scene being accompanied by head motions.

Lightness contrast and assimilation are opposite phenomena: in contrast grey targets appear darker when bordering bright rather than dark surfaces; in assimilation grey targets appear lighter when bordering bright rather than dark surfaces. The underlying neurophysiological mechanisms of these phenomena are not known. The aim of this study was to investigate the relationship between contrast and assimilation, and the timing and levels of perceptual and cognitive processing using combined behavioural and electrophysiological methods. Thirty undergraduate students (23 female, age range 18–48 years) participated in a forced-choice (grey target is lighter/darker than a comparison square) task, using stimuli designed such that the inducers were in two configurations (small and large) and two shades (white and black). The behavioural data (more consistent and faster responses) corroborated previous findings of stronger contrast effects with white inducers and stronger assimilation effects with black inducers. According to the Event-Related Potentials (ERP) results the mean amplitude was larger in conditions with less consistent and slower behavioural responses. Thus, with contrast responses P1 amplitude was larger with black than white inducers, and N1 amplitude was larger to assimilation than contrast when the configuration of the stimulus was held constant. These results suggest contrast may occur as early as P1 (~ 110 ms) and assimilation may occur later in N2 (~ 220 ms), whereas in some conditions, differences in ERPs associated with contrast vs assimilation may happen as early as in N1 (~ 170 m), in occipital and parietal cortical sites. [ABSTRACT FROM AUTHOR]

Visual illusions have been studied extensively, but their time course has not. Here we show, in a sample of more than 550 people, that unrestricted presentation times—as opposed to presentations lasting only a single second—weaken the Ebbinghaus illusion, strengthen lightness contrast with double increments, and do not alter lightness contrast with double decrements. When presentation time is unrestricted, these illusions are affected in the same way (decrease, increase, no change) by how long observers look at them. Our results imply that differences in illusion magnitude between individuals or groups are confounded with differences in inspection time, no matter whether stimuli are evaluated in matching, adjustment, or untimed comparison tasks. We offer an explanation for why these three illusions progress differently, and we spell out how our findings challenge theories of lightness, theories of global-local processing, and the interpretation of all research that has investigated visual illusions, or used them as tools, without considering inspection time. [ABSTRACT FROM AUTHOR]

Objective: The lightness of a surface is not solely determined by the amount of light it reflects but it is also modulated by the surrounding context. Despite a long history of research, neural correlates of context dependent lightness perception remain a question of ongoing debate. The current study seeks to expand upon the existing literature by using a classical effect called simultaneous lightness induction (SLI) as stimulus where a central disk appears darker when embedded in a darker surround compared to when it is embedded in a lighter surround. Methods: We use functional magnetic resonance imaging (fMRI) to investigate locus of processing of context-dependent lightness in visual hierarchy. During the fMRI experiment, we presented ten participants with a dynamic stimulus by modulating the luminance of either achromatic surround (surroundmodulation condition) or achromatic disk (disk-modulation condition) at four different frequencies ranging from 1 to 8 Hz while they perform a demanding fixation task. Results: Behaviorally, when the surround luminance is modulated at low frequencies, participants perceive an illusory change in lightness of the disk (lightness induction). Whereas, they perceive the disk as having constant lightness at higher frequencies. Utilizing this temporal dependence of lightness induction and comparing the fMRI BOLD activity of the surround-modulation condition with that of the disk-modulation condition at different frequencies, while accounting for the effects of long-range luminance changes, we showed that activity in V1 correlates with perceived lightness. However, such a correlation was not evident in extrastriate areas, V2, V3, and V4. Conclusion: The findings of our study provide evidence for the involvement of the primary visual cortex in processing of context-dependent lightness information. [ABSTRACT FROM AUTHOR]

In double increment Simultaneous Lightness Contrast two equiluminant squares rest on darker backgrounds that differ in luminance. Research on such displays has produced conflicting results as to whether an illusion is observed. Anchoring theory of lightness predicts no illusion with double increment displays. Here we test the hypothesis that an illusion can be predicted if the framework containing the target and the darkest background carries more weight in lightness computations. We tested two displays, one with a general white and one with a general black background. An illusion was obtained only in the first display. These results suggest that an illusion can occur with double increment displays when the global value of the targets differs from their local value, as these conditions allow different local framework weighting to affect the targets’ final lightness. We propose that this parameter be added to the Anchoring Theory.

Humans are able to estimate the reflective properties of the surface (albedo) of an object despite the large variability in the reflected light due to shading, illumination and specular reflection. Here we first used a physically based rendering simulation to study how different statistics (i.e. percentiles) based on the luminance distributions of matte and glossy objects predict the overall surface albedo. We found that the brightest parts of matte surfaces are good predictors of the surface albedo. As expected, the brightest parts led to poor performance in glossy surfaces. We then asked human observers to sort four (2 matte and 2 glossy) objects in a virtual scene in terms of their albedo. The brightest parts of matte surfaces highly correlated with human judgments, whereas in glossy surfaces, the highest correlation was achieved by percentiles within the darker half of the objects' luminance distributions. Furthermore, glossy surfaces tend to appear darker than matte ones, and observers are less precise in judging their lightness. We then manipulated different bands of the virtual objects' luminance distributions separately for glossy and matte surfaces. Modulating the brightest parts of the luminance distributions of the glossy surfaces had a limited impact on lightness perception, whereas it clearly influenced the perceived lightness of the matte objects. Our results demonstrate that human observers effectively ignore specular reflections while evaluating the lightness of glossy objects, which results in a bias to perceive glossy objects as darker. [ABSTRACT FROM AUTHOR]

Levin and Banaji ( Journal of Experimental Psychology: General, 135, 501-512, 2006) reported a lightness illusion in which participants appeared to perceive Black faces to be darker than White faces, even though the faces were matched for overall brightness and contrast. Recently, this finding was challenged by Firestone and Scholl ( Psychonomic Bulletin and Review, 2014), who argued that the nominal illusion remained even when the faces were blurred so as to make their race undetectable, and concluded that uncontrolled perceptual differences between the stimulus faces drove at least some observations of the original distortion effect. In this paper we report that measures of race perception used by Firestone and Scholl were insufficiently sensitive. We demonstrate that a forced choice race-identification task not only reveals that participants could detect the race of the blurred faces but also that participants' lightness judgments often aligned with their assignment of race. [ABSTRACT FROM AUTHOR]

Lightness judgments of face stimuli are context-dependent (i.e., judgments of face lightness are influenced by race classification). Here, we tested whether contextual effects in face lightness perception are modulated by expertise, exploiting well-known other race effects in face perception. We used a lightness-matching paradigm where Chinese and White observers were asked to adjust the lightness of a variable face to match that of a standard face. The context (i.e., race category) of the two faces could be the same or different. Our data indicated that both groups had the smallest matching errors in same-context trials, for which errors did not vary across different racial categories. For cross-context trials, observers made the largest (negative) errors when the reference face was Black, as compared to Chinese and White references, for which matching errors were no different from zero or trended positively. Critically, this pattern was similar for both groups. We suggest that contextual influences in lightness perception are unlikely to be guided by classical mechanisms that drive face perception. We instead speculate that such influences manifest in terms of an interaction between race assumptions (e.g., expected surface reflectance patterns) and traditional mechanisms for reflectance computations.

In simultaneous lightness contrast, two identical gray target squares lying on backgrounds of different intensities appear different in lightness. Traditionally, this illusion was explained by lateral inhibitory mechanisms operating retinotopically. More recently, spatial filtering models have been preferred. We report tests of an anchoring theory account in which the illusion is attributed to grouping rules used by the visual system to compute lightness. We parametrically varied the belongingness of two gray target bars to their respective backgrounds so that they either appeared to group with a set of bars flanking them, or they appeared to group with their respective backgrounds. In all variations, the retinal adjacency of the gray squares and their backgrounds was essentially unchanged. We report data from seven experiments showing that manipulation of the grouping rules governs the size and direction of the simultaneous lightness contrast illusion. These results support the idea that simultaneous lightness contrast is the product of anchoring within perceptual groups. [ABSTRACT FROM AUTHOR]

It is well known that visible luminance gradients may generate contrast effects. In this work we present a new paradoxical illusion in which the luminance range of gradual transitions has been reduced to make them invisible. By adopting the phenomenological method proposed by Kanizsa, we have found that unnoticeable luminance gradients still generate contrast effects. But, most interestingly, we have found that when their width is narrowed, rather than generating contrast effects on the surrounded surfaces, they generate an assimilation effect. Both high- and low-level interpretations of this "phantom" illusion are critically evaluated. [ABSTRACT FROM AUTHOR]

The responses of visual neurons in experimental animals have been extensively characterized. To ask whether these responses are consistent with a wholly empirical concept of visual perception, we optimized simple neural networks that respond according to the cumulative frequency of occurrence of local luminance patterns in retinal images. Based on this estimation of accumulated experience, the neuron responses showed classical center-surround receptive fields, luminance gain control and contrast gain control, the key properties of early level visual neurons determined in animal experiments. These results imply that a major purpose of pre-cortical neuronal circuitry is to contend with the inherently uncertain significance of luminance values in natural stimuli.

When looking at an object—say, a banana—we can both directlyperceiveits visual qualities (e.g., its size) and also make higher-leveljudgmentsabout its visual and non-visual properties (e.g., not only its size, but also its cost). Suppose you obtain a rating of a property such as size. Does that rating implicate seeing or merely higher-level judgment? The answer often matters a great deal -- e.g., determining whether such ratings imply “top-down” effects of cognition on perception. Too often, however, this distinction is ignored in empirical investigations of such effects. Here we suggest a simple test for when such ratings can be used to implicate perception: whenever the very same experiment “overgeneralizes” to an unambiguouslynon-perceptual factor, the results cannot be used to draw implications about perception, per se. As a case study, we investigate an empirical report alleging that conservatives perceive Barack Obama as darker skinned than liberals do. Two simple experiments show that the very same effects, measured via the same “representativeness” ratings, obtain with unambiguously non-perceptual and even silly factors (involving bright red horns vs. halos, rather than brightness differences). We suggest that this renders such methods unable to implicate visual processing and we recommend that “overgeneralization tests” of this type always be conducted in such contexts. [ABSTRACT FROM PUBLISHER]

Natural scenes often contain variations in local luminance as a result of cast shadows and illumination from different directions. When making judgments about such scenes, it may be hypothesized that darker regions (with lower relative contrast due to a lack of illumination) are avoided as they may provide less detailed information than well-illuminated areas. We here test this hypothesis, first by presenting participants images of faces that were digitally modified to simulate the effect of a shadow over half of the image, and second by presenting photographs of faces taken with side illumination, also resulting in the appearance of a shadow across half of the face. While participants viewed these images, they were asked to perform different tasks on the images, to allow for the presentation of the different versions of each image (left shadow, right shadow, no shadow), and to distract the observers from the contrast and illumination manipulations. The results confirm our hypothesis and demonstrate that observers fixate the better illuminated regions of the images. [ABSTRACT FROM AUTHOR]

A recent surge of research has revived the notion that higher-level cognitive states such as beliefs, desires, and categorical knowledge can directly change what we see. The force of such claims, however, has been undercut by an absence of visually apparent demonstrations of the form so often appealed to in vision science: such effects may be revealed by statistical analyses of observers' responses, but you cannot literally experience the alleged top-down effects yourself. A singular exception is an influential report that racial categorization alters the perceived lightness of faces, a claim that was bolstered by a striking visual demonstration that Black faces appear darker than White faces, even when matched for mean luminance. Here, we show that this visually compelling difference is explicable in terms of purely low-level factors. Observers who viewed heavily blurred versions of the original Black and White faces still judged the Black face to be darker and the White face to be lighter even when these observers could not perceive the races of the faces, and even when they explicitly judged the faces to be of the same race. We conclude that the best subjectively appreciable evidence for top-down influences on perception does not reflect a genuinely top-down effect after all: instead, such effects arise from more familiar (if subtle) bottom-up factors within visual processing. [ABSTRACT FROM AUTHOR]

The 3D LAMINART model of 3D vision and figure-ground perception is used to explain and simulate a key example of the Venetian blind effect and show how it is related to other well-known perceptual phenomena such as Panum's limiting case. The model proposes how lateral geniculate nucleus (LGN) and hierarchically organized laminar circuits in cortical areas V1, V2, and V4 interact to control processes of 3D boundary formation and surface filling-in that simulate many properties of 3D vision percepts, notably consciously seen surface percepts, which are predicted to arise when filled-in surface representations are integrated into surface-shroud resonances between visual and parietal cortex. Interactions between layers 4, 3B, and 2/3 in V1 and V2 carry out stereopsis and 3D boundary formation. Both binocular and monocular information combine to form 3D boundary and surface representations. Surface contour surface-to-boundary feedback from V2 thin stripes to V2 pale stripes combines computationally complementary boundary and surface formation properties, leading to a single consistent percept, while also eliminating redundant 3D boundaries, and triggering figure-ground perception. False binocular boundary matches are eliminated by Gestalt grouping properties during boundary formation. In particular, a disparity filter, which helps to solve the Correspondence Problem by eliminating false matches, is predicted to be realized as part of the boundary grouping process in layer 2/3 of cortical area V2. The model has been used to simulate the consciously seen 3D surface percepts in 18 psychophysical experiments. These percepts include the Venetian blind effect, Panum's limiting case, contrast variations of dichoptic masking and the correspondence problem, the effect of interocular contrast differences on stereoacuity, stereopsis with polarity-reversed stereograms, da Vinci stereopsis, and perceptual closure. These model mechanisms have also simulated properties of 3D neon color spreading, binocular rivalry, 3D Necker cube, and many examples of 3D figure-ground separation. [ABSTRACT FROM AUTHOR]

A tidal wave of recent research purports to have discovered that higher-level states such as moods, action capabilities, and categorical knowledge can literally and directly affect how things look. Are these truly effects on perception, or might some instead reflect influences on judgment, memory, or response bias? Here, we exploited an infamous art-historical reasoning error (the so-called “El Greco fallacy”) to demonstrate that multiple alleged top-down effects (including effects of morality on lightness perception and effects of action capabilities on spatial perception) cannot truly be effects on perception. We suggest that this error may also contaminate several other varieties of top-down effects and that this discovery has implications for debates over the continuity (or lack thereof) of perception and cognition. [ABSTRACT FROM PUBLISHER]

The Craik-O’Brien-Cornsweet (COC) effect demonstrates that perceived lightness depends not only on the retinal input at corresponding visual areas but also on distal retinal inputs. In the COC effect, the central edge of an opposing pair of luminance gradients (COC edge) makes adjoining regions with identical luminance appear to be different. To investigate the underlying mechanisms of the effect, we examined whether the subjective awareness of the COC edge is necessary for the generation of the effect. We manipulated the visibility of the COC edge using visual backward masking and continuous flash suppression while monitoring subjective reports regarding online percepts and aftereffects of adaptation. Psychophysical results showed that the online percept of the COC effect nearly vanishes in conditions where the COC edge is rendered invisible. On the other hand, the results of adaptation experiments showed that the COC edge is still processed at the early stage even under the perceptual suppression. These results suggest that processing of the COC edge at the early stage is not sufficient for generating the COC effect, and that subjective awareness of the COC edge is necessary.

The variable resolution and limited processing capacity of the human visual system requires us to sample the world with eye movements and attentive processes. Here we show that where observers look can strongly modulate their reports of simple surface attributes, such as lightness. When observers matched the color of natural objects they based their judgments on the brightest parts of the objects; at the same time, they tended to fixate points with above-average luminance. When we forced participants to fixate a specific point on the object using a gaze-contingent display setup, the matched lightness was higher when observers fixated bright regions. This finding indicates a causal link between the luminance of the fixated region and the lightness match for the whole object. Simulations with rendered physical lighting show that higher values in an object's luminance distribution are particularly informative about reflectance. This sampling strategy is an efficient and simple heuristic for the visual system to achieve accurate and invariant judgments of lightness. [ABSTRACT FROM AUTHOR]

Highlights: [•] In a VR study we contrasted the High- and Mid-level theory of lightness perception. [•] The magnitude of the contrast effect depends on the horizontal distance between the backgrounds. [•] Both Mid- and High-level process of visual perception are involved in the contrast phenomenon. [ABSTRACT FROM AUTHOR]

Managing the appearance of images across different display environments is a difficult problem, exacerbated by the proliferation of high dynamic range imaging technologies. Tone reproduction is often limited to luminance adjustment and is rarely calibrated against psychophysical data, while color appearance modeling addresses color reproduction in a calibrated manner, albeit over a limited luminance range. Only a few image appearance models bridge the gap, borrowing ideas from both areas. Our take on scene reproduction reduces computational complexity with respect to the state-of-the-art, and adds a spatially varying model of lightness perception. The predictive capabilities of the model are validated against all psychophysical data known to us, and visual comparisons show accurate and robust reproduction for challenging high dynamic range scenes. [ABSTRACT FROM AUTHOR]

Abstract: A laminar cortical model of stereopsis and 3D surface perception is developed and simulated. The model shows how spiking neurons that interact in hierarchically organized laminar circuits of the visual cortex can generate analog properties of 3D visual percepts. The model describes how monocular and binocular oriented filtering interact with later stages of 3D boundary formation and surface filling-in in the LGN and cortical areas V1, V2, and V4. It proposes how interactions between layers 4, 3B, and 2/3 in V1 and V2 contribute to stereopsis, and how binocular and monocular information combine to form 3D boundary and surface representations. The model suggests how surface-to-boundary feedback from V2 thin stripes to pale stripes helps to explain how computationally complementary boundary and surface formation properties lead to a single consistent percept, eliminate redundant 3D boundaries, and trigger figure-ground perception. The model also shows how false binocular boundary matches may be eliminated by Gestalt grouping properties. In particular, the disparity filter, which helps to solve the correspondence problem by eliminating false matches, is realized using inhibitory interneurons as part of the perceptual grouping process by horizontal connections in layer 2/3 of cortical area V2. The 3D sLAMINART model simulates 3D surface percepts that are consciously seen in 18 psychophysical experiments. These percepts include contrast variations of dichoptic masking and the correspondence problem, the effect of interocular contrast differences on stereoacuity, Panum’s limiting case, the Venetian blind illusion, stereopsis with polarity-reversed stereograms, da Vinci stereopsis, and perceptual closure. The model hereby illustrates a general method of unlumping rate-based models that use the membrane equations of neurophysiology into models that use spiking neurons, and which may be embodied in VLSI chips that use spiking neurons to minimize heat production. [Copyright &y& Elsevier]

Abstract: In a looking-time study, 24 infants 6months of age were presented with continuously folding and unfolding patterns of stripes. The luminances in the dynamic lightness constancy pattern were changed in such way that adults attribute them to changes of the various regions’ orientation relative to the light source (lightness constancy display). The “reversed” lightness constancy stimulus consisted of a continuously folding and unfolding pattern, in which the luminance changes were not consistent with a striped surface illuminated from one side. The only difference between the animations was the relationship between the change in surface orientation and the change of luminances. The infants looked significantly longer at the reversed lightness constancy animation than at the lightness constancy display. This finding suggests that the infants detected the violation of the lightness constancy rules in the reversed lightness constancy stimulus. The infants were also presented with control animations to rule out the possibility that looking preferences were based on low-level properties of the display. [Copyright &y& Elsevier]

Abstract: The purpose of this work is to describe how the visual system groups surfaces of unequal lightness under complex patterns of illumination. We propose that the Gestalt principle of Grouping by Regularity explains this process better than the more often cited principle of Grouping by Similarity. In our first experiment we demonstrate that in a perceptual organization task, pitting proximity against illumination gradients, discounting the illuminant was contingent upon the periodicity of the illuminant. Traditional theories of lightness constancy and discounting the illuminant () cannot account for such effects. Three more experiments show that grouping is affected more by local luminance ratios than constant reflectance ratios. We conclude from these findings that Grouping by Regularity is a powerful grouping principle that operates pre-constancy. [Copyright &y& Elsevier]

Abstract: Recently we developed a model that reproduces the Kanizsa square illusion based on two principles: (1) a spatial 2-D integration of luminance ratio and differentiated depth signals creates a “primary” lightness map and a depth map, respectively, which is then followed by (2) a modification of the primary lightness values under influence of the perceived depth (). Within this model, the process of the spatial integration inevitably introduced an arbitrary offset. In order to obtain absolute values of depth and lightness, the offset values needed to be determined by other constraints. This is the anchoring problem of the depth and lightness measurements. Here we report the anchoring rules that were established by investigating the model’s responses to the Kanizsa square and its wide range of variations. For the primary lightness map, the highest value rule was applied, while the area rule appeared most plausible for the depth map. By applying the same principles to simple figures consisting of black and white areas of different size ratios, the model succeeded in reproducing published empirical results on lightness anchoring (). [Copyright &y& Elsevier]

M. Singh and B. L. Anderson (2002) proposed a perceptual theory of achromatic transparency in which the perceived transmittance of a perceived transparent filter is determined by the ratio of the Michelson contrast seen in the region of transparency to that of the background seen directly. Subsequently, B. L. Anderson, M. Singh, and J. Meng (2006) proposed that Michelson contrast should be replaced by perceived contrast in this theory. However, their experimental stimuli were nongeneric (i.e., special cases), and their observers had little choice in their matching strategy. Here, the author shows that both of their ratio-of-contrasts theories are incorrect and that problems with their theoretical analyses and experimental designs led them to conclude that mean luminance does not affect perceived transmittance when contrast is held constant. The author also shows that B. L. Anderson's (2003) transmittance anchoring principle is not valid when a transparent surface is perceived to penetrate rather than overlay another surface. Finally, the author shows that M. Singh's (2004) theoretical proof that the ratio-of- Michelson-contrasts theory accurately predicts lightness matching through transparency is incorrect. [ABSTRACT FROM AUTHOR]

The high dynamic range of illumination may cause serious distortions and problems in the viewing and further processing of digital images. Important information can be hidden in the highly or extremely lowly illuminated parts. This paper deals with the reproduction of such images and introduces two new tone reproduction preprocessing algorithms which may help in developing the hardly viewable or nonviewable features and content of the images. [ABSTRACT FROM AUTHOR]

Although lightness perception is clearly influenced by contextual factors, it is not known whether knowledge about the reflectance of specific objects also affects their lightness. Recent research by O. H. MacLin and R. Malpass (2003) suggests that subjects label Black faces as darker than White faces, so in the current experiments, an adjustment methodology was used to test the degree to which expectations about the relative skin tone associated with faces of varying races affect the perceived lightness of those faces. White faces were consistently judged to be relatively lighter than Black faces, even for racially ambiguous faces that were disambiguated by labels. Accordingly, relatively abstract expectations about the relative reflectance of objects can affect their perceived lightness. [ABSTRACT FROM AUTHOR]

A laminar cortical model of stereopsis and 3D surface perception is developed and simulated. The model describes how monocular and binocular oriented filtering interact with later stages of 3D boundary formation and surface filling-in in the LGN and cortical areas V1, V2, and V4. It proposes how interactions between layers 4, 3B, and 2/3 in V1 and V2 contribute to stereopsis, and how binocular and monocular information combine to form 3D boundary and surface representations. The model includes two main new developments: (1) It clarifies how surface-to-boundary feedback from V2 thin stripes to pale stripes helps to explain data about stereopsis. This feedback has previously been used to explain data about 3D figure-ground perception. (2) It proposes that the binocular false match problem is subsumed under the Gestalt grouping problem. In particular, the disparity filter, which helps to solve the correspondence problem by eliminating false matches, is realized using inhibitory interneurons as part of the perceptual grouping process by horizontal connections in layer 2/3 of cortical area V2. The enhanced model explains all the psychophysical data previously simulated by Grossberg and Howe (2003), such as contrast variations of dichoptic masking and the correspondence problem, the effect of interocular contrast differences on stereoacuity, Panum's limiting case, the Venetian blind illusion, stereopsis with polarity-reversed stereograms, and da Vinci stereopsis. It also explains psychophysical data about perceptual closure and variations of da Vinci stereopsis that previous models cannot yet explain. [ABSTRACT FROM AUTHOR]

Adelson's tile, snake, and some other lightness illusions of the same type were measured with the Munsell neutral scale for twenty observers. It was shown that theories based on low-level luminance contrast processing could hardly explain these illusions. Neither can those based on luminance X-junctions. On the other hand, Helmholtz's idea, that simultaneous lightness contrast originates from an error in judgement of apparent illumination, has been elaborated so as to account for the tile and snake illusions as well as other demonstrations presented in this report. [ABSTRACT FROM AUTHOR]

Studies on binocular contrast sensitivity have predominantly focused on flat, two-dimensional (2D) gratings. The underlying hypothesis of such studies is that contrast sensitivity is determined at the early stages of visual processing and is not influenced by the process of three-dimensional (3D) shape recovery. However, it can be argued that contrast detection involves identifying changes in albedo of a 3D surface rather than strictly determining the presence of 2D luminance changes. In support of this hypothesis, in three experiments we found that the relative salience of oriented luminance modulations was affected by the disparity content of the stimuli, when the same luminance distribution was assigned to a flat surface or to a surface modulated in depth. In the first experiment, in particular, we found that the relative salience of an oriented luminance grating decreased when it could be interpreted as the shading produced by a Lambertian illumination, rather than a change in reflectance. In the other two experiments, moreover, we found that this effect was reduced when the frequency of the luminance modulation did not match the frequency of the stereo corrugation. These results are consistent with the idea that the appearance of a luminance distribution is affected by the perceived 3D properties of the surface on which the luminance distribution is located. [Copyright &y& Elsevier]

A laminar cortical model of stereopsis and later stages of 3D surface perception is developed and simulated. The model describes how initial stages of monocular and binocular oriented filtering interact with later stages of 3D boundary formation and surface filling-in in the lateral geniculate nucleus and cortical areas V1, V2, and V4. In particular, it details how interactions between layers 4, 3B, and 2/3A in V1 and V2 contribute to stereopsis, and clarifies how binocular and monocular information combine to form 3D boundary and surface representations. Along the way, the model modifies and significantly extends the disparity energy model. Neural explanations are given for psychophysical data concerning: contrast variations of dichoptic masking and the correspondence problem, the effect of interocular contrast differences on stereoacuity, Panum’s limiting case, the Venetian blind illusion, stereopsis with polarity-reversed stereograms, da Vinci stereopsis, and various lightness illusions. By relating physiology to psychophysics, the model provides new functional insights and predictions about laminar cortical architecture. [Copyright &y& Elsevier]