Illusory Streaks from Corners and Their Perceptual Integration

Abstract

Perceptual grouping appears both as organized forms of real figural units and as illusory or “phantom” figures. The phenomenon is visible in the Hermann grid and in configurations which generate color spreading, e.g., “neon effects.” These configurations, generally regular repetitive patterns, appear to be crossed by illusory bands filled with a brighter shade or a colored tinge connecting the various loci of illusory effects. In this work, we explore a particular new illusion showing a grouping effect. It manifests as illusory streaks irradiating from the vertexes of angular contours and connecting pairs of figures nearby. It is only clearly visible when more than one figure is shown, and takes the shape of a net crossing their corners. Although the grouping effect is vivid, the local source of the illusion is completely hidden. Theories explaining this effect as due to the irradiation of illusory streaks (mainly that of Grossberg and Mingolla, 1985a,b) do not fully explain the figural patterns presented here. Illusory effects have already been documented at the angles of various figures, causing them to alter in amplitude and brightness; however, the figure illustrated here appears to have different features and location. Phenomenological observations and an experiment were conducted to assess the role played by geometric and photometric parameters in this illusion. Results showed that sharp angles, in low contrast with the surround, are the main source of the illusion which, however, only becomes visible when at least two figures are close together. These findings are discussed with respect to theories of contour processing and perceptual grouping, and in relation to other illusions.

An Illusory Motion in Stationary Stimuli Alters Their Perceived Duration

“…Similar to the previous experiment, the median rating score for the perceived strength of illusory motion was 5 (95% C.I. = [3,5]), while the control image received a median score of 0 (95% C.I. = [0, 0]).…”

Perceptual Organization

“…Structural ambiguity and uncertainty pose a specific problem here. Perceptual organization not only accounts for the ways in which physically defined order is processed by the visual system, but also how such order may be inferred in cases of uncertainty, and how this may give rise to the perception of "illusory" or "phantom" shapes, as shown recently in a new phenomenon [54] [18,19,58]. In some conditions, figure-ground is solely determined by the orientation of contrasts, not by their relative sign.…”

Design for Ergonomics

“…To solve these issues we use strategies that have been described as laws of perceptual organization that serve to analyze local and global relationships between the points and regions in the visual field even if, in many cases, they can lead to results that are not exactly optimal and that can be qualified as optical illusions (Parlangeli O and Roncato 2010;Roncato et al 2016). These laws were identified for the first time at the beginning of the last century by a group of German psychologists belonging to a current of thought known as Gestalt psychology, and can be seen as heuristics, that is, optimal interpretative strategies, even if not always correct, based on assumptions about the typical structure of the world (Koffka 1935;Wertheimer 1923).…”