Theories
The effect of both optical illusions is often explained by a neural process called lateral inhibition. The intensity at a point in the visual system is not simply the result of a single receptor, but the result of a group of receptors which respond to the presentation of stimuli in what is called a receptive field.
A retinal ganglion cell pools the inputs of several photoreceptors over an area of retina, the area in physical space to which the photoreceptors respond is the ganglion cell's "receptive field". In the center of the receptive field the individual photoreceptors excite the ganglion cell when they detect increased luminance. The photoreceptors in the surrounding area inhibit the ganglion cell. Thus, since a point at an intersection is surrounded by more intensity than a point at the middle of a line, the intersection appears darker due to the increased inhibition.
There is strong evidence that the retinal ganglion cell theory is untenable. For example, making the lines of the grid wavy rather than straight eliminates both the Hermann grid and scintillating grid illusions. The Baumgartner / RGC theory does not predict this outcome. One alternative explanation is that the illusion is due to S1 type simple cells in the visual cortex.
Read more about this topic: Grid Illusion
Famous quotes containing the word theories:
“The wise man regulates his conduct by the theories both of religion and science. But he regards these theories not as statements of ultimate fact but as art-forms.”
—J.B.S. (John Burdon Sanderson)
“The two most far-reaching critical theories at the beginning of the latest phase of industrial society were those of Marx and Freud. Marx showed the moving powers and the conflicts in the social-historical process. Freud aimed at the critical uncovering of the inner conflicts. Both worked for the liberation of man, even though Marx’s concept was more comprehensive and less time-bound than Freud’s.”
—Erich Fromm (1900–1980)
“Whatever practical people may say, this world is, after all, absolutely governed by ideas, and very often by the wildest and most hypothetical ideas. It is a matter of the very greatest importance that our theories of things that seem a long way apart from our daily lives, should be as far as possible true, and as far as possible removed from error.”
—Thomas Henry Huxley (1825–95)