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Explanations of the Ponzo size illusion, the simultaneous contrast illusion, and the Craik-O’Brien-Cornsweet brightness illusions involve either stimulus-driven processes (assimilation, enhanced contrast, and anchoring) or prior experiences. Real-world up-down asymmetries for typical direction of illumination and ground planes in our physical environment should influence these illusions if they are experience based, but not if they are stimulus driven. Results presented here demonstrate differences in illusion strengths between upright and inverted versions of all three illusions. A left-right asymmetry of the Cornsweet illusion was produced by manipulating the direction of illumination, providing further support for the involvement of an experience-based explanation. When the inducers were incompatible with the targets being located at the different distances, the Ponzo illusion persisted and so did the influence from orientation, providing evidence for involvement of processes other than size constancy. As defined here, upright for the brightness illusions is consistent with an interpretation of a shaded bulging surface and a 3D object resulting from a light-from-above assumption triggering compensation for varying illumination. Upright for the Ponzo illusion is consistent with the inducers in the form of converging lines being interpreted as railway tracks receding on the ground triggering size constancy effects. The implications of these results, and other results providing evidence against experience-based accounts of the illusions, are discussed.

Usually, there is a limited depth of field (DOF) for automultiscopic three-dimensional (3D) displays, which requires modifying light fields of 3D scenes to fit into the DOF constraint of a target display. A novel depth-perception preserved 3D content remapping method is presented based on Cornsweet illusion, which uses Cornsweet profile to enhance the depth-perception by augmenting the contrast at the edges. The original depth map is decomposed into multifrequency bands and remapped by reducing the low-frequency bands while preserving the high-frequency parts, which leads to Cornsweet profiles with the preserved perceptual depth. The manipulation of the multifrequency bands is processed in logarithmic domain with a well-designed monotonic mapping function. The tradeoff between displayed blur and depth preservation is achieved by adopting the available objective metric based on human vision system. A warping-based view synthesis method is adopted to retarget the light field according to the modified depth map. Experimental results show that the displayed modified 3D light field appears sharp, and the original perception of depth is maximally preserved.

Rene Jagnow [2012] argues that David Rosenthal's theory of consciousness cannot account for certain experiences that involve colours so fine-grained that we do not and cannot have concepts of them. Jagnow claims that an appeal to comparative concepts such as being slightly darker than cannot help Rosenthal, since, in order to apply such concepts, we would already need to be conscious of two distinct fine-grained colours. The present paper contests this claim. It appeals to the Cornsweet illusion and some other visual phenomena, in order to argue that our visual systems can and do represent brutely comparative matters.

On page 3653, there is a mistake in the explanation of the Cornsweet illusion. In fact, the explanation is that the panel perceived as darker is facing towards the light source—in the case of this figure the light is coming from the right.

In recent years, several techniques have been proposed to simulate the gaze effect of the Human Visual System (HVS). It is believed that this effect is due to the foveation filtering. Current techniques to simulate the foveation filtering in computer graphics are either slow or suffer from artifacts and limitations. In this paper, we present a new approach of foveation filtering based on the Mipmap Pyramid of the current view by considering the relationship between the Gaussian kernel and Mipmap level. Due to the nonlinear Mipmap interpolation under the Bilateral Filtering scheme, we are able to simulate the foveation filtering more naturally and efficiently than in previous work. Moreover, a detail enhancement method based on the Cornsweet illusion is proposed to augment the gazing effect. We demonstrate our new approach with a variety of examples and provide comparisons with recent approaches.

Figure/background organization usually entails that figures are perceived in front of the background, and in special conditions front objects appear transparent. Moreover, depth stratification is constrained by the color contrast between specific areas also when transparency is perceived. In four experiments, we showed that contrast affects surface stratification even when it is artificially produced by Cornsweet illusory contrasts, both by increasing and decreasing the color difference just at the border of the adjacent areas, and also when the colors of all areas, complementary and equiluminant included, are kept constant. The results agree with previous findings in the achromatic domain, both with opaque and transparent colors (Masin, 2000) and stress the relevance of the perceived contrast, instead of color differences, on the perception of transparency and stratification.

Several brightness illusions indicate that borders can affect the perception of surfaces dramatically. In the Cornsweet illusion, two equiluminant surfaces appear to be different in brightness because of the contrast border between them. Here, we report the existence of cells in monkey visual cortex that respond to such an “illusory” brightness. We find that luminance responsive cells are located in color-activated regions (cytochrome oxidase blobs and bridges) of primary visual cortex (V1), whereas Cornsweet responsive cells are found preferentially in the color-activated regions (thin stripes) of second visual area (V2). This colocalization of brightness and color processing within V1 and V2 suggests a segregation of contour and surface processing in early visual pathways and a hierarchy of brightness information processing from V1 to V2 in monkeys.

In order to reveal the extent of the anisotropy and individual differences in stereoscopic depth contrast and Cornsweet illusion in depth, the magnitudes of these effects were measured with different slant orientations for 26 observers. About 30% of observers showed a prominent anisotropy for depth contrast, while the anisotropy was not found for Cornsweet illusion in depth in spite of the previous research studies. The correlation between the results of these experiments was not significant (r=0.163), suggesting that multiple factors affect these two illusions.

The strength of the Craik–O'Brien–Cornsweet illusion was measured for different values of spatial and temporal stimulus parameters, in the traditional achromatic version, and in an isoluminant colour version. It was found that the illusion is much weaker with isoluminant colour stimuli than with achromatic luminance stimuli. The illusion depends on the spatial parameters of the stimulus in a way that yields an approximate scale invariance: The strength of the illusion is similar for different stimulus sizes, as long as the ratio of the width of the transition region around the edge, where luminance or colour change, to the total stimulus width is preserved. In both the achromatic and the chromatic case, the strength of the illusion decreases with increasing presentation time. The similarity of the differences between brightness and colour effects on one hand and the differences in sensitivity for colour and luminance changes in humans on the other suggests that a lack of gradient detection underlies the Craik–O'Brien–Cornsweet illusion.

It is both a technical and an artistic challenge to depict three-dimensional content using stereo equipment and a flat two-dimensional screen. On the one hand, the content needs to fit within the limits of a given display technology and at the same time achieve a comfortable viewing experience. Given the technological advances of 3D equipment, especially the latter increases in importance. Modifications to stereo content become necessary that aim at flattening or even removing binocular disparity to adjust the 3D content to match the comfort zone in which the clash between accommodation and vergence stays acceptable. However, applying such modifications can lead to a reduction of crucial depth details. One promising direction is backwardcompatible stereo, for which the disparity is low enough that overlaid stereo pairs seem almost identical. It builds upon the Craik-O'Brien-Cornsweet effect, a visual illusion, which uses so-called Cornsweet profiles to produce a local contrast that leads to a perceived brightness increase. Similarly, Cornsweet profiles in disparity can lead to an illusion of depth. Applying them skilfully at depth discontinuities allows for a reduction of the overall disparity range to ensure a comfortable yet convincing stereo experience. The present work extends the previous idea by showing that Cornsweet profiles can also be used to enhance the 3D impression. This operation can help in regions where the disparity range was compressed, but also to emphasize parts of a scene. A user study measures the performance of backward-compatible stereo and our disparity enhancement.

Much research has gone into developing methods for enhancing the contrast of displayed 3D scenes. In the current study, we investigated the perceptual impact of an algorithm recently proposed by Ritschel et al.1 that provides a general technique for enhancing the perceived contrast in synthesized scenes. Their algorithm extends traditional image-based Unsharp Masking to a 3D scene, achieving a scene-coherent enhancement. We conducted a standardized perceptual experiment to test the proposition that a 3D unsharp enhanced scene was superior to the original scene in terms of perceived contrast and preference. Furthermore, the impact of different settings of the algorithm's main parameters enhancement-strength (λ) and gradient size (σ) were studied in order to provide an estimate of a reasonable parameter space for the method. All participants preferred a clearly visible enhancement over the original, non-enhanced scenes and the setting for objectionable enhancement was far above the preferred settings. The effect of the gradient size σ was negligible. The general pattern found for the parameters provides a useful guideline for designers when making use of 3D Unsharp Masking: as a rule of thumb they can easily determine the strength for which they start to perceive an enhancement and use twice this value for a good effect. Since the value for objectionable results was twice as large again, artifacts should not impose restrictions on the applicability of this rule.

We present a new approach for enhancing local scene contrast by unsharp masking over arbitrary surfaces under any form of illumination. Our adaptation of a well-known 2D technique to 3D interactive scenarios is designed to aid viewers in tasks like understanding complex or detailed geometric models, medical visualization and navigation in virtual environments. Our holistic approach enhances the depiction of various visual cues, including gradients from surface shading, surface reflectance, shadows, and highlights, to ease estimation of viewpoint, lighting conditions, shapes of objects and their world-space organization. Motivated by recent perceptual findings on 3D aspects of the Cornsweet illusion, we create scene coherent enhancements by treating cues in terms of their 3D context; doing so has a stronger effect than approaches that operate in a 2D image context and also achieves temporal coherence. We validate our unsharp masking in 3D with psychophysical experiments showing that the enhanced images are perceived to have better contrast and are preferred over unenhanced originals. Our operator runs at real-time rates on a GPU and the effect is easily controlled interactively within the rendering pipeline.

Humans perceive a low-contrast Craik-O’Brien-Cornsweet (COC) grating as being similar to, or even indiscriminable from, a squarewave grating (Fig. l), despite the fact that the spatial intensity profiles of the two patterns are very different [3]. This similarity has been attributed to processing at early stages of the visual pathway which selectively transmits edge information, followed by cortical mechanisms which “fill in” the appropriate intensities between the edges [9]. Here we find that bees behave as though they experience a similar illusion, suggesting that certain principles of visual processing are shared by insects and humans. While the visual systems of insects and humans display several differences an obvious one being that insects possess compound (multi-faceted) eyes whilst humans possess simple (single lens) eyes recent work is beginning to reveal several parallels with regard to the ways in which the two systems process visual information. For example, bees, like humans, possess trichromatic vision [ 161, are “colour-blind” with respect to the detection of motion [ 12, 131, appear to analyse pattern orientation by using orientation-tuned channels [20, 211 and even exhibit “top-down” processing with regard to the ability to detect camouflaged objects [22]. Indeed, insects even seem to experi

Many single-unit electrophysiological studies of visual cortex have investigated strong evoked responses to simple stimuli such as oriented gratings. Experiments involving other types of stimuli, such as natural scenes, higher-order features, and surface brightness, produce single-unit responses that are more difficult to interpret. Experiments with brightness, in particular, evoke single-unit responses that are typically weakly modulated. When the brightness is generated by a visual illusion such as the Cornsweet illusion, statistical tests are often necessary to distinguish true responses from baseline fluctuations. Here, using data collected from cat Areas 17 and 18 in response to real and illusory brightness stimuli, we provide a method for detecting and quantifying weak but significant periodic responses. By randomizing spike trains (via bootstrap methods), we provide confidence levels for response significance, permitting the evaluation of both weak and strong responses. We show that because of a strong dependence on total spike number, response significance can only be appropriately determined with randomized spike trains of similar spike number. Such randomizations can be performed for both stimulus-elicited and spontaneously occurring spike trains. By developing a method for generating randomized modulated spike trains (phase-restricted randomization) from actual recordings, we calculate upper and lower confidence limits of modulated spike trains and describe how measurement precision varies as a function of total spike count. Finally, using this randomization method, we describe how a correction function can be determined to correct for measurement bias introduced at low spike counts. These methods may also be useful in the study of small but potentially significant responses in other systems.

This paper presents a summary of experimental findings, theoretical models and unresolved issues regarding border effects on brightness, of which the Cornsweet illusion (Cornsweet, 1970 Visual Perception. Academic Press: New York) is the best-known example. It is argued that no current theoretical model completely accounts for the wide variety of effects described. Contrast sensitivity function (CSF) models can explain many low-contrast, but not high-contrast, border effects. Lightness integration models based on Land and McCann's retinex theory (Land and McCann, 1971. J. Opt. Soc. Am. 61, pp. 1-11) have the advantage over CSF models in that they predict transitivity of border effects where they are found to occur. However, they fail to predict the appearance of a variety of Cornsweet-like figures, have never been tested with relatively high contrast versions of those figures, and have only been implemented by qualitative demonstration. It is argued that edge-detector models are potentially the most promising theoretical candidates but, as with lightness-integration models, they have invariably relied on qualitative demonstrations and have only dealt with low-contrast border effects. A computational edge-detector model which predicts the appearance of both high and low contrast Cornsweet figures is proposed and its advantages over other models, as well as its current limitations, are discussed. The final section discusses the neural locus for border effects in brightness.

A stereo analogue of the Cornsweet luminance illusion was discovered, and measured by a null method. Two flat vertical textured surfaces in the frontoparallel plane met at a vertical boundary, at which the left-hand surface curved slightly forward and the right-hand surface curved back by an equal amount. The protruding left edge was jointed to the receding right edge by a step. Result: although the two flat surfaces were equidistant, the left surface appeared to be about half a centimetre nearer to the observer than the right surface.

Naval Submarine Medical Research Laboratory, Groton, Connecticut The appearance of the Cornsweet illusion was assessed quantitatively by obtaining measures of the overall perceived contrast of the illusion stimulus and by obtaining magnitude estimations of the apparent homogeneity/evenness of brightness on either side of the luminance discontinuity, including brightness in the neighborhood of the discontinuity. The perceived broad-area contrast of the illusion matched the physical contrast of a comparison step-function stimulus for physical contrasts of 0.2 and below. Ratings of homogeneity of brightness of the illusion tended to be maximal for those same values of physical contrast.

Measurements were made of the perceived contrast that results from the Cornsweet illusion as a function of the edge contrast and edge width. The physical contrast was varied from 3% to 5%, and the visual extent of the Cornsweet edge varied from 0.1 degrees to 3.0 degrees on each side. Results show that, for low-contrast (less than 20%) and wide edges, the Cornsweet edge yields as much contrast as a real-step lumininance transition with the same edge magnitude. At high contrast (30%-40%) the illusion is reduced relative to a real step, regardless of whether the illusion consists of a conventional Cornsweet edge or an additive combination of a real step and a Cornsweet edge. As a general rule, wide edges yield more contrast than narrow edges. The results are interpreted in terms of the visual describing funtion; a nonlinear model is proposed. The correspondence between the predictions of the model and the perceptual measurements on the Cornsweet edges is good.

We have generated an auditory loudness illusion by amplitude modulating either a noise or a sinusoid using a temporal pattern analogous to the spatial luminance patterns used by Craik, O'Brien, and Cornsweet. The stimulus is gated on at a constant amplitude for some foreperiod, then, for example, the intensity is slowly decreased over a 100‐msec interval by 10 dB, then rapidly increased by 20 dB, then slowly decreased again to the initial amplitude where it remains for an interval equal to the foreperiod. Subjects adjusted the intensities of two square‐gated stimuli to match the loudnesses of the segments of the modulated stimulus before and after modulation. The results indicate that the stimulus following the modulation sounds 3 to 6 dB more intense than the stimulus preceding the modulation, when in fact the intensities are equal. Reversing the modulation reverses the direction of the effect. We will present examples and discuss the frequency, intensity, and temporal parameters that influence the magnitude of the illusion. [Supported by the NIH.]

Jesteadt, Green, and Weir [Percept. Psychophys. 23, 244–250 (1978)] found that the second of two equally intense tones was heard as louder when the tones were separated by intensity transitions which decayed slowly and rose abruptly: an auditory analog of the Cornsweet illusion in vision. The experiments to be reported attempt to distinguish two types of explanation of this effect: (i) that slow changes in intensity are less perceptually salient than fast, (ii) that the attack, or onset of a note is more salient in determining loudness than is offset. Preliminary experiments indicate that the attack is more important than the relative amount of rapid or slow intensity changes. [Work supported by Science Research Council, U.K.]