Decoding the subjective rotation direction of the spinning dancer from fMRI data. Using a contrast illusion to teach principles of neural processing. Making sense of the Hermann Grid illusion. S1 simple-cell theory proposes that the illusion is caused by how S1-type simple cells in the primary visual cortex respond to certain visual stimuli.
Evidence supporting this theory includes the fact that the illusion is not dependent upon the size of the grid and that the illusion still occurs when the contrast of the image is reversed. S1 simple-cell theory may be more helpful for understanding the illusion.Lateral inhibition happens when the excitation of surrounding neurons inhibits a neuron's response to a stimulus. This theory suggests that the brightest at the intersections forces retinal cells to adjust the intensity. Lateral inhibition is often used to explain the Hermann grid illusion, but more recent evidence suggests that this might not be why the illusion happens.Like many optical illusions, different theories have been proposed to explain exactly why this happens. Notice how the dots at the center of each intersection seem to shift between white and gray? Sometimes we see things that aren't there, and the Hermann Grid illusion is a great example.
