Computational Mechanisms Responsible for the Hermann Grid Illusion

Psychophysical research on the Hermann grid illusion is reviewed and possible neurophysiological mechanisms are discussed. The illusion is most plausibly explained by lateral inhibition within the concentric receptive fields of retinal and/or geniculate ganglion cells, with contributions by the binocular orientation-specific cortical cells. Results may be summarized as follows: (a) For a strong Hermann grid illusion to be seen bar width must be matched to the mean size of receptive-field centers at any given retinal eccentricity. (b) With the use of this rationale, the diameter of foveal perceptive-field centers (the psychophysical correlate of receptive-field centers) has been found to be in the order of 4–5 min arc and that of total fields (centers plus surrounds) 18 min arc. These small diameters explain why the illusion tends to be absent in foveal vision. (c) With increasing distance from the fovea, perceptive-field centers increase to 1.7 deg at 15 deg eccentricity and then to 3.4 deg at 60 deg eccentricity. This doubling in diameter agrees with the change in size of retinal receptive-field centers in the monkey. (d) The Hermann grid illusion is diminished with dark adaptation. This finding is consistent with the reduction of the center—surround antagonism in retinal receptive fields. (e) The illusion is also weakened when the grid is presented diagonally, which suggests a contribution by the orientation-sensitive cells in the lateral geniculate nucleus and visual cortex. (f) Strong induction effects, similar to the bright and dark spots in the Hermann grid illusion, may be elicited by grids made of various shades of grey; and by grids varying only in chroma or hue. Not accounted for are: the illusory spots occurring in an outline grid ie with hollow squares, and the absence of an illusion when extra bars are added to the grid. Alternative explanations are discussed for the spurious lines connecting the illusory spots along the diagonals and the fuzzy dark bands traversing the rhombi in modified Hermann grids.

Download Full-text

The Use of the Cancellation Technique to Quantify the Hermann Grid Illusion

PLoS ONE ◽

10.1371/journal.pone.0000265 ◽

2007 ◽

Vol 2 (2) ◽

pp. e265 ◽

Cited By ~ 4

Author(s):

Piers D.L. Howe ◽

Margaret S. Livingstone

Keyword(s):

Hermann Grid Illusion

Download Full-text

Global Factors in the Hermann Grid Illusion

Perception ◽

10.1068/p130033 ◽

1984 ◽

Vol 13 (1) ◽

pp. 33-40 ◽

Cited By ~ 27

Author(s):

Jeremy M Wolfe

Keyword(s):

Receptive Fields ◽

Illusion Magnitude ◽

Local Model ◽

Hermann Grid Illusion

Most explanations of the Hermann grid illusion are local in nature. For example, in Baumgartner's model the effect is generated by the response of cells having concentric on—off or off—on receptive fields. Such models predict that the magnitude of the illusion at a given intersection should be the same whether that intersection is viewed in isolation or in conjunction with other intersections in a grid. Two experiments are reported. The first demonstrates that illusion magnitude grows with the number of intersections. The second shows that this growth is seen when the intersections are arranged in an orderly grid but not when they are placed irregularly. These results suggest that a purely local model for the Hermann grid illusion is not a complete explanation. Global factors must be involved.

Download Full-text

Dark adaptation and the Hermann grid illusion

Perception & Psychophysics ◽

10.3758/bf03198695 ◽

1976 ◽

Vol 20 (1) ◽

pp. 10-12 ◽

Cited By ~ 10

Author(s):

Eugene R. Wist

Keyword(s):

Dark Adaptation ◽

Hermann Grid Illusion

Download Full-text

A few observations on Hermann Grid stimuli

10.31234/osf.io/4fjnq ◽

2020 ◽

Author(s):

Bernt Skottun

Keyword(s):

Visual System ◽

Dark Background ◽

Hermann Grid Illusion

The Hermann Grid is made up of a series of vertical and horizontal bars. The Hermann Grid Illusion consists in the brightness of the intersections appearing different from that of the sections between intersections in spite of the luminance being the same. In the case of a light grid on a dark background the intersections tend to appear darker than the parts between intersections. It is here pointed out, in two different ways, that the stimulus power is less for the parts of the grid located at intersections than for parts of the grid between intersections. This is all in the stimuli and does not depend on vision or the visual system. Were we to assume that a stronger stimulus gives a brighter appearance this would make the parts between intersections appear brighter than the parts of the grid at intersections. This would be consistent with the Hermann Grid Illusion.

Download Full-text

Chromatic and achromatic processing in the Hermann Grid illusion

Journal of Vision ◽

10.1167/4.8.328 ◽

2004 ◽

Vol 4 (8) ◽

pp. 328-328 ◽

Cited By ~ 1

Author(s):

J. P. Comerford ◽

B. Bodkin ◽

F. Thorn

Keyword(s):

Hermann Grid Illusion

Download Full-text

The Curved Grid Non-Illusions

10.1093/acprof:oso/9780199794607.003.0045 ◽

2017 ◽

Author(s):

János Geier ◽

Mariann Hudák

Keyword(s):

Statistical Analysis ◽

Retinal Ganglion Cells ◽

Line Width ◽

Ganglion Cells ◽

Receptive Fields ◽

Retinal Ganglion ◽

Illusory Effect ◽

Grid Line ◽

Wide Range ◽

Hermann Grid Illusion

The generally accepted explanation of the Hermann grid illusion is Baumgartner’s hypothesis that the illusory effect is generated by the response of retinal ganglion cells with concentric ON-OFF or OFF-ON receptive fields. To challenge this explanation, some simple distortions to the grid lines were introduced that make the illusion disappear totally, while all preconditions of Baumgartner’s hypothesis remained unchanged. Psychophysical experiments in which the distortion tolerance was measured showed the level of distortion at which the illusion disappears at a given type of distortion for a given subject. Statistical analysis shows that the distortion tolerance is independent of grid-line width within a wide range and of the type of distortion, except when one side of each line remains straight. The conclusion is the main cause of the Hermann grid illusion is the straightness of the edges of the grid lines. Similar results have been obtained in the scintillating grid.

Download Full-text