Concentric chromatic gradient affects color appearance of central targets

Distinct Mechanisms Mediate Visual Detection and Identification

This study determined the effects of achromatic and multichromatic targets and darts on throwing. Subjects were 56 college men assigned to one of four dart-and-target throwing conditions as follows: white target--white darts, white target--multi-colored darts, multi-colored target--white darts, and multi-colored target--multi-colored darts. Subjects threw from 20 ft. using an overhand throwing pattern. The main effect of target color and the interaction of target color and dart color were significant. The results indicated that white backgrounds are superior to colored backgrounds. Also, the interactions of colored darts against a white background produced the best combination for performance. In target tasks which depend upon response-produced feedback, color of figures and background interact apparently to affect motor performance.

Photoreceptor sensitivity changes explain color appearance shifts induced by large uniform backgrounds in dichoptic matching

Starting from an achromatic display used by Zavagno to study a glare and a ‘smoke’ effect, we show two new dynamic effects that we call (a) ‘light explosion’ and (b) ‘night crash’. On a uniform white or black background four black or white rectangles (inducers, 1 deg × 5.7 deg) were arranged to form an orthogonal cross with a square gap in its centre. (a) When the luminance of black inducers on a white background is transformed into a smooth gray scale gradient with the lighter ends facing the square gap, a luminous mist with a glare effect is seen. When such a transformation is performed dynamically by changing the gradient from outside to inside (with the outside ends remaining black and the inside changing toward white), a sudden explosion of light is seen. (b) When the luminance of white inducers on a black background is transformed into a smooth gray scale gradient with their darker ends facing the square gap, a sort of dark ‘smoke’ is seen. If such a transformation is performed dynamically by changing the gradient from inside to outside (with the outside ends remaining white and the inside changing toward black), a sudden and instantaneous black diffusion (a sort of night crash) is seen. Both the light explosion and the night crash effects have an exponential course followed by an immediate drop. Psychophysical data show that both effects depend on an interaction between the lightness of the background, the lightness of the square gap, and the transformation rate of the gray scale gradient.

Regarding the ocean background, the painted camouflage on the surface of targets effectively conceals them, providing a strategic defense against military reconnaissance. Accurately predicting the color appearance of both the target and background is crucial for assessing the camouflage’s performance. This study investigates the perceived color attributes (lightness, chroma, and hue) of marine targets against varying ocean backgrounds using memory matching assessments. Visual data reveal that background color slightly influences target hue perception through simultaneous contrast effects, while lightness and chroma remain unaffected. As the image-based color appearance model – iCAM offers a potential solution for extracting color appearance attributes from a complex RGB image, it has been adopted to predict the pixel-wise color appearance of the marine targets. Comparative validation shows iCAM substantially outperforms existing color appearance models in marine environments, establishing its superior capability for naval camouflage assessment and design. Further analysis indicates that chroma predictions are sensitive to changes in the filter kernel size of iCAM and the image size, while lightness and hue predictions remain stable. Notably, undersized kernels systematically underestimate perceived chroma, highlighting the critical importance of parameter optimization.

The aim of this study was to evaluate the effect of thickness on the color appearance and translucency parameter (TP) of multilayer CAD/CAM composite resin blocks. Four brands of A3-shade multilayer CAD/CAM composite resin blocks were examined (Katana Avencia, CERASMART Multi, KZR-CAD HR Block 4 E-va, and Block HC Hard AN). Six specimens of five thicknesses were prepared for each brand, yielding 120 specimens in total. CIEL*a*b* values were determined using a spectrophotometer against black and white backgrounds, and the TP was calculated. The color differences (ΔE00) between layers (cervical/middle/incisal) and brands for each thickness against the black background were calculated using the CIEDE2000 system. As a result, on the black background, L* of the incisal layer was greater while a* and b* were smaller than those of the cervical layer for all brands. The ΔE00 values between the cervical and middle layers (1.23-3.27) were smaller than those between the cervical and incisal layers (3.98-5.67) and those between the middle and incisal layers (3.14-5.92). TP decreased with increasing block thickness. Some TP differences between layers were significant, but they were less than 2.75. In conclusion, the color appearance of CAD/CAM blocks was significantly influenced by both the thickness and layer. L*a*b* decreased with thickness, and a negative exponential relationship between TP and thickness was observed for all layers and brands.

We recorded from single neurons in the parvocellular layers of the lateral geniculate body of anesthetized monkeys. Spectral response curves of parvocellular neurons depended on the luminance ratio between the chromatic stimuli and achromatic background. From response/intensity curves, we determined the relative luminance between a coloured and an achromatic (white) light at which a given cell became non-responsive (critical luminance ratio, CLR). The spectral dependence of the CLRs of narrow (N) and wide band (W) cells with opponent receptor input showed characteristic differences. The activity of W-cells increased with luminance increase of a white light and of a coloured light in the specific spectral region of the cell (yellow-red for the long wave length sensitive WL-, and yellow-green-blue for the short wave length sensitive WS-cells), while N-cells were activated by their specific spectral light (blue for NS-cells, red for NL-cells) and by a luminance decrease of achromatic white. N-cells discriminate best between their characteristic colour and white at luminance ratios below their respective CLR, while W-cells distinguish best between a light of their characteristic colour and white at chromatic/achromatic luminance ratios above their respective CLR. Yellow sensitive W-cells with a narrow spectral sensitivity peaking around 570 nm and with only a small or no response to white light, could enable distinction between white and yellow of similar luminance. The findings are consistent with the opponency model of spectrally sensitive cells in the LGB. We discuss their implications for colour coding by parvocellular cells. N- and W-cells appear to behave complementary with respect to luminance information (N-cells may be compared to the cat's off-cells, W-cells to on-cells). S- and L-cells are complementary with respect to colour. The yellow sensitive WM-cells are critical for the discrimination of yellow and white, while cells with excitatory cone input from blue and red cones (W-SL-cells) may aid the perception of purple. The fact that, at different relative luminance ratios between a chromatic stimulus and a white background, the whole family of parvocellular cells is involved differently in coding for colour, may explain the different appearance of colours against a white background at different luminance ratios and the perception of induced colours.

Recent psychophysical experiments demonstrate that for simple configurations, colour appearance is largely determined by the ratios of within-type cone excitations (cone contrasts) between a target surface and its immediate background. Other experiments demonstrate that both the mean and variance of the cone excitations from remote surfaces may influence the colour of a target surface. The relative contribution of local and remote surfaces to the colour appearance of a centrally viewed target also depends on adaptational state and, therefore, on stimulus duration. Cone-contrast models of colour appearance that include the influence of cone excitations from local and global surfaces may be viewed as modern-day successors of the Retinex model for colour constancy. Here we describe psychophysical experiments of colour matching under simulated illumination changes, and examine the effects of the size and configuration of local and remote chromatic elements in a complex background on the colour appearance of a central target. We compare the observed colour matches with predictions from a standard Retinex model and from a modified Retinex-like model with weighting factors on the distance-order of chromatic edges.

Perceived segmentation of center from surround by only illusory contours causes chromatic lateral inhibition

When single cones are stimulated with spots of 543-nm light presented against a white background, subjects report percepts that vary between predominately red, white, and green. However, light of the same spectral composition viewed over a large field under normal viewing conditions looks invariably green and highly saturated. It remains unknown what stimulus parameters are most important for governing the color appearance in the transition between these two extreme cases. The current study varied the size, intensity and retinal motion of stimuli presented in an adaptive optics scanning laser ophthalmoscope. Stimuli were either stabilized on target locations or allowed to drift across the retina with the eye's natural motion. Increasing both stimulus size and intensity led to higher likelihoods that monochromatic spots of light were perceived as green, whereas only higher intensities led to increases in perceived saturation. The data also show an interaction between size and intensity, suggesting that the balance between magnocellular and parvocellular activation may be critical factors for color perception. Surprisingly, under the range of conditions tested, color appearance did not depend on whether stimuli were stabilized. Sequential activation of many cones does not appear to drive hue and saturation perception as effectively as simultaneous activation of many cones.

We investigated how the chromatic properties of background surfaces affect color constancy using two-dimensional stimuli in a haploscopic view. The reference and test stimuli, illuminated by D65 and chromatic illuminants (red, green, blue, and yellow), consisted of a central 1.2° test patch, a 4.2° Mondrian-like background, and a peripheral 0.4° gray fringe. We used the neutral background and chromatic red-, green-, blue-, and yellow-dominated backgrounds, in which these patch colors were systematically shifted to one color direction while keeping the hue circle. In the first two conditions, both the reference and test feature the same background (neutral and complementary to the illuminant color). In contrast, in the last two conditions, the reference and test stimuli feature different backgrounds, and the expected color appearance of the backgrounds, except at the fringe, looks similar (the color of the illuminant and neutral). The results showed a notable decline in color constancy in the last two conditions, suggesting that the effectiveness of adaptation and illuminant estimation is reduced by the smaller stimulation difference between the reference and test, as well as by the unexpected spatial color structure, even though the cue itself still exists.

Many models of color constancy assume that the visual system estimates the scene illuminant and uses this estimate to determine an object's color appearance. A version of this illumination-estimation hypothesis, in which the illuminant estimate is associated with the explicitly perceived illuminant, was tested. Observers made appearance matches between two experimental chambers. Observers adjusted the illumination in one chamber to match that in the other and then adjusted a test patch in one chamber to match the surface lightness of a patch in the other. The illumination-estimation hypothesis, as formulated here, predicted that after both matches the luminances of the light reflected from the test patches would be identical. The data contradict this prediction. A second experiment showed that manipulating the immediate surround of a test patch can affect perceived lightness without affecting perceived illumination. This finding also falsifies the illumination-estimation hypothesis.

Brightness judgments are a key part of the primate brain’s visual analysis of the environment. There is general consensus that the perceived brightness of an image region is based not only on its actual luminance, but also on the photometric structure of its neighborhood. However, it is unclear precisely how a region’s context influences its perceived brightness. Recent research has suggested that brightness estimation may be based on a sophisticated analysis of scene layout in terms of transparency, illumination and shadows. This work has called into question the role of low-level mechanisms, such as lateral inhibition, as explanations for brightness phenomena. Here we describe experiments with displays for which low-level and high-level analyses make qualitatively different predictions, and with which we can quantitatively assess the trade-offs between low-level and high-level factors. We find that brightness percepts in these displays are governed by low-level stimulus properties, even when these percepts are inconsistent with higher-level interpretations of scene layout. These results point to the important role of low-level mechanisms in determining brightness percepts. INTRODUCTION

The Emergence of Contrast-Invariant Orientation Tuning in Simple Cells of Cat Visual Cortex

In glaucoma, the density of retinal ganglion cells is reduced. It is largely unknown how this influences retinal information processing. An increase in spatial summation and a decrease in contrast gain control and contrast adaptation have been reported. A decrease in lateral inhibition might also arise. This could result in a larger than expected response to some stimuli, which could mask ganglion cell loss on functional testing (structure-function discrepancy). The aim of this study was to compare lateral inhibition between glaucoma patients and healthy subjects; we used a case-control design. Cases (n = 18) were selected to have advanced visual field loss in combination with a normal visual acuity. Controls (n = 50) were not allowed to have symptoms or signs of any eye disease. Lateral inhibition was measured psychophysically on a computer screen, with (1) a modified illusory movement experiment and (2) a contrast sensitivity (CS) test. Illusory movement was quantified by nulling it with a real movement; measure of lateral inhibition was the amount of illusory movement. CS was measured at 1 and 4 cycles per degree (cpd); measure of lateral inhibition was the difference between log CS at 4 and 1 cpd. Both measures were compared between cases and controls; analyses were adjusted for age and gender. There was no difference between cases and controls for these two measures of lateral inhibition (p = 0.58 for illusory movement; p = 0.20 for CS). The movement threshold was higher in cases than in controls (p = 0.008) and log CS was lower, at both 1 (-0.20; p = 0.008) and 4 (-0.28; p = 0.001) cpd. Our results indicate that spatially antagonistic mechanisms are not specifically affected in glaucoma, at least not in the intact center of a severely damaged visual field. This suggests that the structure-function discrepancy in glaucoma is not related to a decrease in lateral inhibition.