The Tilted Hermann Grid Illusion: ‘Illusory Spots’ versus ‘Phantom Bands’

Abstract

The Hermann grid illusion became a cause célèbre, when it was reported that small figural changes from straight to curved bars abolish the dark illusory spots. We demonstrate that this is not an all-or-none effect; rather, the visual system tolerates some tilt/curviness. We transformed straight and curved Hermann grids to rhombic Motokawa grids by gradually tilting the horizontal bars. Initially, we observed only dark illusory spots, then dark spots combined with phantom bands traversing the rhomb along the minor axis, and finally dark phantom bands only. This shows that two kinds of illusions can coexist in the same grid pattern.

Tiny Squares at the Hermann Grid Corners Can Completely Remove the Illusion

“…The perturbation proposed in this work also has some similarity with that proposed by Geier et al. (2008) where the grids become wavy and the visual system tolerates some tilt/curviness as Hamburger et al. (2012) have shown.…”

“…A common neural mechanism may underlie both these phenomena of Mach band and Hermann grating. The perturbation proposed in this work also has some similarity with that proposed by Geier et al (2008) where the grids become wavy and the visual system tolerates some tilt/curviness as Hamburger et al (2012) have shown. We have also proposed that in correspondence to the distortion tolerance defined by Geier et al (2005) for Hermann grid, there exists a gray-level intensity threshold for the present perturbing stimuli in order to make the illusory blobs disappear completely.…”

“…The phenomenon of appearance of these spots remains tolerant across a wide range of variations in contrast, spacing, angular rotation, and so on (Spillmann, 1994). Ever since its inception, the Hermann grid illusion has remained a constant subject of study in visual psychophysics through the works of Hering (1920), Baumgartner (1960), Spillmann and Levine (1971), Spillmann (1994), De Lafuente and Ruiz (2004), Geier, Bernáth, Hudák, and Séra (2008), Hamburger, Baier, and Spillmann (2012), and many others. The effect was generally explained by Baumgartner’s (1960) hypothesis that the illusory blobs at the junction of the grids are generated by the excitatory-inhibitory response of the receptive field of the retinal ganglion cells, till there came several challenges to this explanation during the past three decades (Geier et al., 2008; Lingelbach, Block, Hatzky, & Reisinger, 1985; Schiller & Carvey, 2005; Spillmann, 1994).…”

Illusory Streaks from Corners and Their Perceptual Integration

“…The grouping effect related to perceptual illusions involving elements of various brightness levels is well-known (see Figure 6 ). The illusory diagonals in Figures 1A and 3B may have the same origin as the illusory lines or “streets” in the patterns of Ehrenstein ( Redies and Spillmann, 1981 ; Zucker and Cavanagh, 1985 ; Kitaoka, 2001 ; Hamburger et al, 2012 ) and those generated as neon lights. In the former ( Figure 6A ), perpendicular black lines are erased in the crossing regions, eliciting the perception of disks of a brighter shade than the surround, and diagonal bands connecting the illusory disks in a “street” of equally enhanced brightness.…”

Introducing the scintillating starburst: Illusory ray patterns from spatial coincidence detection

“…Briefly, a rhombic alignment of the lattice seems to abolish the dark spots at the intersection points of the Hermann grid, instead dark "phantom bands" seem to appear. However, it has been pointed out that these are two separate phenomena that are not competing directly but can coexist in the same stimulus (Hamburger et al, 2012). Be that as it may, there are several important differences between phantom bands and the illusory rays in the scintillating starburst.…”