Cornsweet Effect Research Articles

Temporal characteristics of the Craik–O’Brien–Cornsweet effect as revealed by high-speed motion correspondence

Temporal characteristics of the Craik–O’Brien–Cornsweet effect as revealed by high-speed motion correspondence

A Compound Computational Model for Filling-In Processes Triggered by Edges: Watercolor Illusions.

The goal of our research was to develop a compound computational model with the ability to predict different variations of the “watercolor effects” and additional filling-in effects that are triggered by edges. The model is based on a filling-in mechanism solved by a Poisson equation, which considers the different gradients as “heat sources” after the gradients modification. The biased (modified) contours (edges) are ranked and determined according to their dominancy across the different chromatic and achromatic channels. The color and intensity of the perceived surface are calculated through a diffusive filling-in process of color triggered by the enhanced and biased edges of stimulus formed as a result of oriented double-opponent receptive fields. The model can successfully predict both the assimilative and non-assimilative watercolor effects, as well as a number of “conflicting” visual effects. Furthermore, the model can also predict the classic Craik–O'Brien–Cornsweet (COC) effect. In summary, our proposed computational model is able to predict most of the “conflicting” filling-in effects that derive from edges that have been recently described in the literature, and thus supports the theory that a shared visual mechanism is responsible for the vast variety of the “conflicting” filling-in effects that derive from edges.

Diamond Patterns: Cumulative Cornsweet Effects and Motion-Induced Brightening.

A Cornsweet edge creates the perception of a step in surface lightness between two adjacent regions of identical mean luminance due to a gradient on both sides. We might imagine that in a concatenated set of these gradients, the lightness steps would accumulate, but they do not. However, a diamond pattern, with each diamond filled with an identical luminance gradient does give a cumulative Cornsweet effect. Here, we offer an illumination explanation for why the cumulative effect is visible in the diamonds but not in the basic ramp grating and we demonstrate that when the diamonds drift, they produce a strong brightening effect (depending on the direction of the motion) and a dimming aftereffect. These effects are consistent with the local luminance gradients and not with the global lightness shift of the cumulative Cornsweet effect.

Free-Energy and Illusions: The Cornsweet Effect

In this paper, we review the nature of illusions using the free-energy formulation of Bayesian perception. We reiterate the notion that illusory percepts are, in fact, Bayes-optimal and represent the most likely explanation for ambiguous sensory input. This point is illustrated using perhaps the simplest of visual illusions; namely, the Cornsweet effect. By using plausible prior beliefs about the spatial gradients of illuminance and reflectance in visual scenes, we show that the Cornsweet effect emerges as a natural consequence of Bayes-optimal perception. Furthermore, we were able to simulate the appearance of secondary illusory percepts (Mach bands) as a function of stimulus contrast. The contrast-dependent emergence of the Cornsweet effect and subsequent appearance of Mach bands were simulated using a simple but plausible generative model. Because our generative model was inverted using a neurobiologically plausible scheme, we could use the inversion as a simulation of neuronal processing and implicit inference. Finally, we were able to verify the qualitative and quantitative predictions of this Bayes-optimal simulation psychophysically, using stimuli presented briefly to normal subjects at different contrast levels, in the context of a fixed alternative forced choice paradigm.

Cortical dynamics of surface lightness anchoring, filling-In, and perception

This study proposes how the visual cortex may process natural images under variable illumination conditions to generate surface lightness percepts. It is known that visual representations can adapt to a million-fold change in luminance. How such adaptation also anchors percepts of surface lightness to use the full dynamic range of neurons remains an unsolved problem. Such an anchoring of lightness helps to make an image look natural. Anchoring properties include articulation, insulation, configuration, and area effects (e.g., Gilchrist et al., 1999). A cortical model is developed that quantitatively simulates such psychophysical data, as well as psychophysical data about discounting the illumination gradient and the Cornsweet effect, among others. The model is also consistent with a range of anatomical and neurophysiological data about how the brain may use boundary representations to gate the filling-in of surface lightness via horizontal cortical interactions. The model filling-in mechanism runs a thousand times faster than mechanisms of previous biological filling-in models, and thereby helps to clarify how filling-in can occur at the speeds shown in perceptual experiments. The model can process natural images even under dim moonlight and dazzling sunlight. Application of the model to color domain illustrates that it is also able to process natural color images.

Temporal properties of the chromatic and achromatic Craik–O’Brien–Cornsweet effect

The Craik–O’Brien–Cornsweet effect (COCE) is a visual illusion in which a difference in brightness is observed between two regions of equal luminance separated by a contrast edge with opposite luminance gradients on each side. The COCE also occurs with chromatic contrasts. It has been hypothesized that the COCE is mediated by a cortical filling-in process. According to the filling-in hypothesis, the filling-in or spreading of neural activity proceeds at finite speed, and therefore exhibits some temporal tuning as a function of the width of the area to be filled in. In the present study, observers varied the temporal frequency of a COC grating to determine the maximum temporal frequency at which a temporal modulation of brightness or color was perceived. In the achromatic COCE, contours were modulated along the luminance axis of the DKL color space; in the chromatic COCE, contours were modulated either along the L − M or the S − (L + M) axis. For the achromatic condition, the critical temporal frequency at which the COCE was still perceived had the shape of an inverted U, inconsistent with the filling-in hypothesis: the critical temporal frequency increased with increasing spatial frequency only up to 0.2 cycles/deg, but then decreased for higher spatial frequencies. For the chromatic COCE, the critical temporal frequency decreased with increasing spatial frequency, which is also inconsistent with filling-in. Thus, the results of the present study are inconsistent with the idea that the temporal dynamics of the COCE, both achromatic and chromatic, are due to filling-in. Instead, our results are consistent with the spatial filtering properties of the luminance and chromatic systems.

Phenomenology and psychophysics

Recent philosophy of mind has tended to treat “inner” states, including both qualia and intentional states, as “theoretical posits” of either folk or scientific psychology. This article argues that phenomenology in fact plays a very different role in the most mature part of psychology, psychophysics. Methodologically, phenomenology plays a crucial role in obtaining psychophysical results. And more importantly, many psychophysical data are best interpreted as reporting relations between stimuli and phenomenological states, both qualitative and intentional. Three examples are used to argue for this thesis: the Weber–Fechner laws, the Craik-O’Brien–Cornsweet effect, and subjective contour figures. The phenomenological properties that play a role here do so in the role of data that ultimately constrain theoretical work (in this case theory of vision), and not as theoretical posits.

An Empirical Explanation of the Cornsweet Effect

A long-standing puzzle in vision is the assignment of illusory brightness values to visual territories based on the characteristics of their edges (the Craik-O'Brien-Cornsweet effect). Here we show that the perception of the equiluminant territories flanking the Cornsweet edge varies according to whether these regions are more likely to be similarly illuminated surfaces having the same material properties or unequally illuminated surfaces with different properties. Thus, if the likelihood is increased that these territories are surfaces with similar reflectance properties under the same illuminant, the Craik-O'Brien-Cornsweet effect is diminished; conversely, if the likelihood is increased that the adjoining territories are differently reflective surfaces receiving different amounts of illumination, the effect is enhanced. These findings indicate that the Craik-O'Brien-Cornsweet effect is determined by the relative probabilities of the possible sources of the luminance profiles in the stimulus.

Response from Maddess, Srinivasan and Davey

Pessoa and Neumann[1]summarize our results well and the comparison made with the results of De Weerd et al.[2]is interesting, provocative and worthy of experimental testing. They don't mention that, like De Weerd et al., we also find that cortical measures determine the speed of construction of illusory brightness. We showed that our observed flicker fusion frequencies for `Craik–O'Brien–Cornsweet effect' (COCE) gratings of different stripe widths could most simply be understood if one assumed a constant cortical propagation velocity, calculated as either 155 or 205mm.s−1 depending on whether V1 or V2 was involved. Other authors have reported that illusory brightness and actual brightness perception also take time and may involve a filling-in process[3, 4].

The Craik-O'Brien-Cornsweet effect and brightness induction both proceed by the spreading of brightness information.

The Craik-O'Brien Cornsweet effect (COCE) is a visual illusion where the luminance of image boundaries sets the apparent brightness of enclosed regions. The COCE may be produced by the cortex constructing the observed brightness through a lateral 'filling-in' process: propagating brightness information from the edges of the enclosed regions towards their centres. Any such filling-in process would imply a speed of propagation. Data on the propagation speed of brightness information in two different brightness induction effects are compared using a multivariate regression analysis. We demonstrate similar non-zero speeds for the COCE and for a brightness contrast effect.

The chromatic cornsweet effect

The Cornsweet effect was measured using equiluminous chromatic gradients as well as with an achromatic gradient. The chromatic Cornsweet effect is smaller than the achromatic effect.

An inducing mechanism of the Craik-O'Brien and the Cornsweet effects (author's transl)

The effect of edges on apparent lightness of the uniform luminous field was investigated in the so-called Craik-O'Brien and Cornsweet patterns as compared with that in the edgeless uniform field. It was found that white edge in the Craik-O'Brien pattern of Type II as well as a black edge in that of Type I lowered or darkened apparent lightness of the field on both side of the edge. The so-called Craik-O'Brien effect was due to assymmetry of the edge-effect on the two sides. The darkening effect of the white edge was explained by the antagonistic lateral inhibition. The same effect of the black edge was explained by a newly introduced concept of non-antagonistic inhibition. The Cornsweet effect was a combination of two edges, white and black, but not simply a summation but a complicated interaction of them.