Most Findings Obtained With Untimed Visual Illusions Are Confounded

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.

The Brain Knows enough to take into account Light and Shadow

ABSTRACTVisual perception requires to infer object and light source color to maintain constancy. This study demonstrates the influences of environmental sunlight color trajectory (blue-white-yellow-red), and associated color of scattered light in shadows on color perception. In Adelson’s checkerboard shadow illusion, squares of equal luminance appear lighter or darker depending on whether they are inside or outside a cast shadow1. In some color variations, illusion magnitude is attenuated by specific colors of the cast shadow. Particularly in the green monotone environment (green checkerboard under green ambient and diffusion light), illusion magnitude reduces down nearly to zero. In contrast, shading by structure is not affected by the color environment. Thus, the cast shadow and shading by structure have distinct effects on surface color constancy. This illusion attenuation may be related to the absence of green in the natural environmental light spectrum, including in cast shadows. The brain may utilize the implicit learned trajectory of natural light to resolve ambiguity in surface reflectance. Our results provide a new formula not only to understand, but also to generate new variations of other illusions such as #The Dress.

Characterizing the whiteness dependence of the Hermann and Scintillating Grid visual illusions

The Hermann Grid and the Scintillating Grid are among the most prominent brightness-contrast illusions. Perception of these illusions is sensitive to a wide range of image parameters including color, linearity of the edges, and visual size of the images. Here we characterize the influence of three prominent parameters that influence grid illusion perception--dot whiteness, line whiteness, and background whiteness. Experimental data was obtained from several volunteer groups that were tasked with scoring the magnitude of the illusion for images exhibiting different whiteness levels of these three grid elements. Analysis of the data revealed a significant dependence of illusion perception on the whiteness of grid elements. Surprisingly, illusion perception effectively disappeared after an intermediate threshold of whiteness for the dot, line, and background elements in both the Scintillating Grid and Hermann Grid. Moreover, increasing the size of elements decreased the illusion magnitude. The results of this study quantify the whiteness-dependence of brightness-contrast grid illusions and may motivate new experiments to understand the neural mechanisms that are responsible for their perception.

The Fraser-Wilcox Illusion and Its Extension

The Fraser-Wilcox illusion is one of the anomalous motion illusions observed in a stationary image, and its extension, including “rotating snakes,” which has been used extensively via the Internet, are reviewed in this chapter. Perceptual dimorphism featuring the Fraser-Wilcox illusion is explained by an interaction between two different illusions. Darkening disambiguation of the Fraser-Wilcox illusion, perceptual dimorphism, the optimized Fraser-Wilcox illusions, the effect of age on the illusion magnitude, as well as the role of color including color enhancement are demonstrated and discussed. The timing-difference model and the eye-movement model are also explored. Recent studies that relate to these concepts are also examined.

Decrement of the Brentano Müller-Lyer Illusion as a Function of Inspection Time

Two experiments are reported in which the decline or decrement in the magnitude of the Brentano Müller-Lyer illusion was measured. Observers made a pre-test judgment and, after a variable intervening time period, a post-test judgment of illusion magnitude. In experiment 1, the intervening time periods were 1, 2, and 3 min during which time the independent groups of observers allocated to each of the three time periods either systematically scanned the Brentano figure (inspection conditions) or waited until the intervening period had elapsed (no-inspection conditions). Experiment 2, which included an additional 5 min intervening time period, evaluated a response-bias explanation for the results of the inspection conditions of experiment 1. Taken together, the findings of the two experiments indicate that sheer inspection of the Brentano figure produces illusion decrement. However, illusion decrement was independent of the duration of the inspection period, with equivalent amounts of decrement occurring across the range of viewing times examined in the two experiments. The pattern of these results suggests that theories of Müller-Lyer decrement must incorporate a factor attributable to, or correlated with, inspection time, whose effect in reducing illusion magnitude is confined mainly to the first 1 or 2 min of active visual inspection of the Brentano illusion figure.

Ebbinghaus Illusion: Effect of Figural Similarity upon Magnitude of Illusion When Context Elements are Equal in Perceived Size

The magnitude of the Ebbinghaus illusion has been reported to be greater when test element and context elements are figurally similar as opposed to figurally dissimilar. In the current investigation with 16 observers, illusion magnitude was greater for a figurally similar configuration even though the context elements of the figurally similar configuration were perceived as smaller than the context elements of a figurally dissimilar configuration. Hence, figural similarity appears to have a prepotent effect in the Ebbinghaus illusion.