Simultaneous Brightness Contrast Research Articles

Simultaneous brightness contrast with three different stimuli: 2D, 3D, and D‐up

AbstractIn this study, simultaneous brightness contrast was investigated using three different devices: 2D (paper), 3D (space), and D‐up. The paper stimuli were made by printing papers, the space stimuli were produced by illumination in a two‐rooms experimental booth, and the D‐up stimuli were shown to subjects using a D‐up viewer. The brightness of test patches was judged by the amounts of whiteness and blackness. The results were different among the devices; however, if the whiteness of the test patches was plotted for the luminance contrast of the test patch versus the surround, all the data points were expressed by nonlinear equations. Data from the space stimuli were expressed by only one equation; those from the paper stimuli were also expressed by the nonlinear equation but with different coefficients for each test patch. The results from D‐up were between those of the space and paper experiments. All the results were explained in relation to the hypothesized illuminated space over the surrounds. The difference among devices was explained by the whiteness of the surround being transferred to the illumination.

Mechanisms underlying simultaneous brightness contrast: Early and innate

In the phenomenon of simultaneous brightness contrast, two patches, one on a dark background and the other on a light one, appear to have different brightness despite being physically equi-luminant. Elucidating the phenomenon’s underlying mechanisms is relevant for the larger question of how the visual system makes photometric judgments in images. Accounts over the past century have spanned low-, mid- and high-level visual processes, but a definitive resolution has not emerged. We present three studies that collectively demonstrate that the computations underlying this phenomenon are low-level, instantiated prior to binocular fusion, and available innately, without need for inferential learning via an individual’s visual experience. In our first two studies, we find that strong brightness induction is obtained even when observers are unaware of any luminance differences in the neighborhoods of the probe patches. Results with dichoptic displays reveal that eye of origin, although not evident consciously, has a marked influence on the eventual brightness percept of the probe patches, thereby localizing brightness estimation to a site preceding binocular fusion. The third study uses conventional simultaneous brightness contrast displays, but an unusual group of participants: Congenitally blind children whom we were able to treat surgically. The results demonstrate an immediate susceptibility to the simultaneous brightness illusion after sight onset. Together, these data strongly constrain the search for mechanisms underlying a fundamental brightness phenomenon.

Sonification supports perception of brightness contrast

In complex visual representations, there are several possible challenges for the visual perception that might be eased by adding sound as a second modality (i.e. sonification). It was hypothesized that sonification would support visual perception when facing challenges such as simultaneous brightness contrast or the Mach band phenomena. This hypothesis was investigated with an interactive sonification test, yielding objective measures (accuracy and response time) as well as subjective measures of sonification benefit. In the test, the participant’s task was to mark the vertical pixel line having the highest intensity level. This was done in a condition without sonification and in three conditions where the intensity level was mapped to different musical elements. The results showed that there was a benefit of sonification, with higher accuracy when sonification was used compared to no sonification. This result was also supported by the subjective measurement. The results also showed longer response times when sonification was used. This suggests that the use and processing of the additional information took more time, leading to longer response times but also higher accuracy. There were no differences between the three sonification conditions.

An adaptive scale Gaussian filter to explain White's illusion from the viewpoint of lightness assimilation for a large range of variation in spatial frequency of the grating and aspect ratio of the targets.

The variation between the actual and perceived lightness of a stimulus has strong dependency on its background, a phenomena commonly known as lightness induction in the literature of visual neuroscience and psychology. For instance, a gray patch may perceptually appear to be darker in a background while it looks brighter when the background is reversed. In the literature it is further reported that such variation can take place in two possible ways. In case of stimulus like the Simultaneous Brightness Contrast (SBC), the apparent lightness changes in the direction opposite to that of the background lightness, a phenomenon often referred to as lightness contrast, while in the others like neon colour spreading or checkerboard illusion it occurs opposite to that, and known as lightness assimilation. The White’s illusion is a typical one which according to many, does not completely conform to any of these two processes. This paper presents the result of quantification of the perceptual strength of the White’s illusion as a function of the width of the background square grating as well as the length of the gray patch. A linear filter model is further proposed to simulate the possible neurophysiological phenomena responsible for this particular visual experience. The model assumes that for the White’s illusion, where the edges are strong and quite a few, i.e., the spectrum is rich in high frequency components, the inhibitory surround in the classical Difference-of-Gaussians (DoG) filter gets suppressed, and the filter essentially reduces to an adaptive scale Gaussian kernel that brings about lightness assimilation. The linear filter model with a Gaussian kernel is used to simulate the White’s illusion phenomena with wide variation of spatial frequency of the background grating as well as the length of the gray patch. The appropriateness of the model is presented through simulation results, which are highly tuned to the present as well as earlier psychometric results.

Individual Variability in Simultaneous Contrast for Color and Brightness: Small Sample Factor Analyses Reveal Separate Induction Processes for Short and Long Flashes.

In classic simultaneous color contrast and simultaneous brightness contrast, the color or brightness of a stimulus appears to shift toward the complementary (opposite) color or brightness of its surrounding region. Kaneko and colleagues proposed that simultaneous contrast involves separate “fast” and “slow” mechanisms, with stronger induction effects for fast than slow. Support for the model came from a diverse series of experiments showing that induction by surrounds varying in luminance or color was stronger for brief than long presentation times (10–40 vs. 80–640 ms). Here, to further examine possible underlying processes, we reanalyzed 12 separate small data sets from these studies using correlational and factor analytic techniques. For each analysis, a principal component analysis of induction strength revealed two factors, with one Varimax-rotated factor accounting for brief and one for long durations. In simultaneous brightness experiments, separate factor pairs were obtained for luminance increments and decrements. Despite being based on small sample sizes, the two-factor consistency among 12 analyses would not be expected by chance. The results are consistent with separate fast and slow processes mediating simultaneous contrast for brief and long flashes.

The Oriented Difference-of-Gaussians Model of Brightness Perception

The Oriented Difference-of-Gaussians (ODOG) model of brightness perception is based on linear spatial filtering by oriented receptive fields followed by contrast/response normalization. The ODOG model can parsimoniously predict the perceived intensity (brightness) of regions in many visual stimuli including White's effect. Unlike competing explanations such as anchoring theory, filling-in, edge-integration, or layer decomposition, spatial filtering by the ODOG model accounts for the gradient structure of induction which, while most striking in grating induction, also occurs within the test fields of classical simultaneous brightness contrast and the White stimulus. Because the ODOG model does not require defined regions of interest it can be applied to arbitrary stimuli, including natural images. We give a detailed description of the ODOG model and illustrate its operation on the Black and White Mondrian stimulus similar to that used by Land & McCann [31] to demonstrate their Retinex model of lightness perception/constancy.

Limitations of the Oriented Difference of Gaussian Filter in Special Cases of Brightness Perception Illusions.

The Oriented Difference of Gaussian (ODOG) filter of Blakeslee and McCourt has been successfully employed to explain several brightness perception illusions which include illusions of both brightness-contrast type, for example, Simultaneous Brightness Contrast and Grating Induction and the brightness-assimilation type, for example, the White effect and the shifted White effect. Here, we demonstrate some limitations of the ODOG filter in predicting perceived brightness by comparing the ODOG responses to various stimuli (generated by varying two parameters, namely, test patch length and spatial frequency) with experimental observations of the same.

The Oriented Difference of Gaussians (ODOG) model of brightness perception: Overview and executable Mathematica notebooks.

The Oriented Difference of Gaussians (ODOG) model of brightness (perceived intensity) by Blakeslee and McCourt (Vision Research 39:4361-4377, 1999), which is based on linear spatial filtering by oriented receptive fields followed by contrast normalization, has proven highly successful in parsimoniously predicting the perceived intensity (brightness) of regions in complex visual stimuli such as White's effect, which had been believed to defy filter-based explanations. Unlike competing explanations such as anchoring theory, filling-in, edge-integration, or layer decomposition, the spatial filtering approach embodied by the ODOG model readily accounts for the often overlooked but ubiquitous gradient structure of induction which, while most striking in grating induction, also occurs within the test fields of classical simultaneous brightness contrast and the White stimulus. Also, because the ODOG model does not require defined regions of interest, it is generalizable to any stimulus, including natural images. The ODOG model has motivated other researchers to develop modified versions (LODOG and FLODOG), and has served as an important counterweight and proof of concept to constrain high-level theories which rely on less well understood or justified mechanisms such as unconscious inference, transparency, perceptual grouping, and layer decomposition. Here we provide a brief but comprehensive description of the ODOG model as it has been implemented since 1999, as well as working Mathematica (Wolfram, Inc.) notebooks which users can employ to generate ODOG model predictions for their own stimuli.

Paradoxical effect of spatially homogenous transparent fields on simultaneous contrast illusions

In simultaneous brightness contrast (SBC) demonstrations, identical mid-luminance disks appear different from each other when one is placed on a black background while the other is placed on a white background. The strength of SBC effects can be enhanced by placing a semi-transparent layer on top of the display (Meyer's effect). Here, we try to separate the causes of Meyer's effect by placing a spatially homogenous transparent layer over a standard SBC display, and systematically varying the transmission level (alpha=0, clear; alpha=1, opaque) and color (black, gray, white) of the semi-transparent layer. Spatially homogenous transparent layers, which lack spatial cues, cannot be unambiguously interpreted as transparent fields. We measure SBC strength with both matching and ranking procedures. Paradoxically, with black layers, increasing alpha level weakens SBC when measured with a ranking procedure (no Meyer's effect) and strengthens SBC when measured with a matching procedure (Meyer's effect). With white and gray layers, neither procedure produces Meyer's effect. We account for the differences between white and black layers by positing that the visual system separates luminance from contrast. The results suggest that observers attend to different information in the matching and ranking procedures.

Flashed stimulation produces strong simultaneous brightness and color contrast

Simultaneous brightness contrast and simultaneous color contrast are classical illusions that demonstrate how our perception can be altered by spatial context; a central gray region appears to have brightness and color that are complementary to those of a surrounding region. Previous studies have suggested the involvement of a sluggish process in these illusions. On the other hand, a different, fast mechanism has recently been postulated to operate in simultaneous contrast when the stimulus is presented only briefly. Here, we show that in briefly flashed stimuli, not only the simultaneous brightness contrast but also the simultaneous color contrast is perceived with greatly enhanced illusion strength. In simultaneous brightness contrast, inserting a spatial gap between the center and surround weakened the illusion only when the stimulus was flashed. In simultaneous color contrast, the gap weakened the illusion irrespective of stimulus duration. Both brightness contrast and color contrast effects steeply decayed with duration. The present study suggests the existence of a fast-responding process for estimating brightness/color primarily based on local difference in luminance/color along the edge between the center and surround. We argue that the sluggishness of simultaneous contrast demonstrated by previous studies originated from a sluggish process after local and fast spatial interactions.

Simultaneous brightness contrast of foragingPapiliobutterflies

This study focuses on the sense of brightness in the foraging Japanese yellow swallowtail butterfly, Papilio xuthus. We presented two red discs of different intensity on a grey background to butterflies, and trained them to select one of the discs. They were successfully trained to select either a high intensity or a low intensity disc. The trained butterflies were tested on their ability to perceive brightness in two different protocols: (i) two orange discs of different intensity presented on the same intensity grey background and (ii) two orange discs of the same intensity separately presented on a grey background that was either higher or lower in intensity than the training background. The butterflies trained to high intensity red selected the orange disc of high intensity in protocol 1, and the disc on the background of low intensity grey in protocol 2. We obtained similar results in another set of experiments with purple discs instead of orange discs. The choices of the butterflies trained to low intensity red were opposite to those just described. Taken together, we conclude that Papilio has the ability to learn brightness and darkness of targets independent of colour, and that they have the so-called simultaneous brightness contrast.

Context-dependent brightness priming occurs without visual awareness

Our visual systems account for stimulus context in brightness perception, but whether such adjustments occur for stimuli that we are unaware of has not been established. We therefore assessed whether stimulus context influences brightness processing by measuring unconscious priming with metacontrast masking. When a middle-gray disk was presented on a darker (or brighter) background, such that it could be consciously perceived as brighter (or darker) via simultaneous brightness contrast (SBC), reaction times were significantly faster to a bright (or dark) annulus than to a dark (or bright) annulus. We further show that context-dependent brightness priming does not correlate with visibility using an objective measure of awareness (Experiment 1) and that context-dependent, but not context-independent brightness priming, occurs equally strongly for stimuli below or above the subjective threshold for awareness (Experiment 2). These results suggest that SBC occurs at early levels of visual input and is not influenced by conscious perception.

Role of orientation enhancement at early phase of visual processing to generate simultaneous brightness contrast and White's illusion

Role of orientation enhancement at early phase of visual processing to generate simultaneous brightness contrast and White's illusion

Contextual Illusions Reveal the Limit of Unconscious Visual Processing

The perception of even the most elementary features of the visual environment depends strongly on their spatial context. In the study reported here, we asked at what level of abstraction such effects require conscious processing of the context. We compared two visual illusions that alter subjective judgments of brightness: the simultaneous brightness contrast illusion, in which two circles of identical physical brightness appear different because of different surround luminance, and the Kanizsa triangle illusion, which occurs when the visual system extrapolates a surface without actual physical stimulation. We used a novel interocular masking technique that allowed us to selectively render only the context invisible. Simultaneous brightness contrast persisted even when the surround was masked from awareness. In contrast, participants did not experience illusory contours when the inducing context was masked. Our findings show that invisible context is resolvable by low-level processes involved in surface-brightness perception, but not by high-level processes that assign surface borders through perceptual completion.

Simultaneous Mean Brightness Preservation and Contrast Improvement via Multi-Peak Histogram Equalization

Histogram Equalization is a traditional image improvement method for enhancing image contrast. However, this image contrast improvement is unsuitable for some consumer electronic applications since mean brightness of output image is different from that of the original image. Nevertheless, when the average brightness of the output image is close to the mean brightness of the original image, its contrast is also decreased thereby reducing efficiency of contrast improvement algorithm. In this paper, we propose a method that not only preserves the mean brightness but also improves the contrast of the output image. By separating the Histogram into Sub-histograms or Multi-peak histogram based on local minima, each sub-histogram will be spread out in a maximum dynamic range based on their gray level interval proportions. Subsequently, the conventional histogram equalization is independently applied to sub-histogram of each peak. To preserve the mean brightness, positions of local minima will be finely adjusted by shifting them within a certain gray scale interval. During each adjustment, sub-histograms of the two local minima which connected to the new local minimum point are re-equalized again. Finally, standard deviation will be normalized in order to improve contrast of the output image.

Spatial filtering versus anchoring accounts of brightness in staircase and simultaneous brightness contrast stimuli

Spatial filtering versus anchoring accounts of brightness in staircase and simultaneous brightness contrast stimuli

A probabilistic explanation of simultaneous brightness contrast

A probabilistic explanation of simultaneous brightness contrast

Coming to terms with lightness and brightness: Effects of stimulus configuration and instructions on brightness and lightness judgments

To recover surface reflectance and illuminance from the raw luminance signal, the visual system must use prior assumptions and strategies that make use of additional sources of information. Indeed, it has been found that depending on experimental conditions, lightness (apparent reflectance) may refer to judgments that are similar to brightness judgments (apparent luminance), that are similar to local brightness-contrast judgments, or that represent an independent third dimension of achromatic experience which exists only when the illumination across regions of the display is visibly non-uniform (L. E. Arend & B. Spehar, 1993a, 1993b). This means that lightness data generated in one experimental condition may not be comparable to lightness data measured in other conditions. We investigate this problem with regard to a history of data on simultaneous brightness-contrast by measuring brightness, brightness-contrast, and lightness in stimuli similar to those used in Gilchrist's edge-substitution studies (A. Gilchrist, S. Delman, & A. Jacobsen, 1983) and in stimuli similar to those used to test Gilchrist's intrinsic-image model against his newer anchoring model (A. Gilchrist, 2006). Our results clarify confusions that appear to stem from comparing different types of lightness judgments and from inadvertently using brightness as an index of lightness under conditions where independent lightness judgments are possible.

Multiresolution wavelet framework models brightness induction effects

A new multiresolution wavelet model is presented here, which accounts for brightness assimilation and contrast effects in a unified framework, and includes known psychophysical and physiological attributes of the primate visual system (such as spatial frequency channels, oriented receptive fields, contrast sensitivity function, contrast non-linearities, and a unified set of parameters). Like other low-level models, such as the ODOG model [Blakeslee, B., & McCourt, M. E. (1999). A multiscale spatial filtering account of the white effect, simultaneous brightness contrast and grating induction. Vision Research, 39, 4361–4377], this formulation reproduces visual effects such as simultaneous contrast, the White effect, grating induction, the Todorović effect, Mach bands, the Chevreul effect and the Adelson–Logvinenko tile effects, but it also reproduces other previously unexplained effects such as the dungeon illusion, all using a single set of parameters.

Koffka's Ring Effect Depends on Thickness, Not Continuity

AbstractMore than 70 years ago Gestalt psychologist Kurt Koffka described a fascinating effect1,2: When a contiguous grey ring is placed on a background half of one shade of grey (different from the ring) and half of another shade of grey, the ring appears to be a homogenous. However, if the ring is slightly divided, now the two halves of the ring appear different shades of grey with the half of the ring on the darker background appearing lighter than the half of the ring on the darker background. The Gestalt principle of continuity in visual perception is invoked to explain this effect. Here we show that in fact when the ring is made thinner it appears heterogeneous even when contiguous. Furthermore, when viewing a thick ring after first viewing a thin ring, the thick ring now too appears heterogenous! These effects are also demonstrated with a colored background and backgrounds with more than two regions. We show that standard simultaneous brightness and color contrast weaken with larger test patches. Thus, Koffka's ring effect is due to vanishingly weak simultaneous contrast for a sufficiently thick ring, not continuity.