Imagine you have a grid of black lines on a white background, like a checkerboard. Now, at the intersections where the lines meet, you might notice faint grayish spots, even though there's no gray in the actual grid. BrainHQ: Another Version of Hermann Grid This is the Hermann Grid Illusion. Your brain plays a trick on you, making it seem like there are gray blobs where there aren't any. It happens because of how our eyes and brain work together to process the contrast and patterns in the grid. Even though it's just black and white lines, your brain interprets it in a way that creates these illusory gray spots at the intersections.

The Hermann Grid Illusion is a visual phenomenon rooted in the complex interplay of retinal processing and lateral inhibition within the human visual system. When exposed to a grid of intersecting black and white lines, viewers often perceive illusory gray spots at the intersections. This can be attributed to the interaction of receptive fields in the retina and lateral inhibition—a neural process in which the activity of one neuron suppresses the activity of its neighbors.

The illusion is particularly interesting when considered in the context of center-surround organization in visual processing. Receptive fields of retinal ganglion cells have a center-surround structure, where stimulation in the center excites the cell, while stimulation in the surround inhibits it. In the case of the Hermann Grid, the bright lines at the intersections activate the center of the receptive fields, leading to a perceived increase in brightness, while the darker regions between lines activate the surround, causing inhibition.

Moreover, the Hermann Grid Illusion is connected to the concept of contrast enhancement and edge detection in early visual processing. The visual system enhances the perception of edges and contrasts, but in this case, it can lead to the illusory perception of gray spots where there is no actual change in luminance.

References

• Hermann, L. (1870). Eine Erscheinung simultanen Contrastes. Pflüger's Archiv für die gesamte Physiologie des Menschen und der Tiere, 3(1), 13-15.
• Maffei, L., & Fiorentini, A. (1973). The unresponsive regions of visual cortical receptive fields. Vision Research, 13(12), 2735-2739.
• Hubel, D. H., & Wiesel, T. N. (1962). Receptive fields, binocular interaction and functional architecture in the cat's visual cortex. The Journal of Physiology, 160(1), 106-154.