An optical illusion is the phenomenon in which visual stimuli are perceived by the eyes and interpreted by the brain in a way that diverges from objective reality. Optical Illusions exploit the complex interactions between the visual system and cognitive processes, causing the spectator to experience images, patterns, or motions that do not correspond to the actual physical properties of the stimulus. Optical Illusions are classified into three principal categories: literal illusions, where the perceived image differs from the components; physiological illusions, arising from overstimulation of the visual system; and cognitive illusions, which result from the brain’s reliance on learned assumptions and unconscious inference.

Optical Illusions reveal the brain’s predictive and constructive nature, demonstrating how perception is shaped by context, contrast, and prior knowledge. Iconic examples include ambiguous figures like Rubin’s Vase, motion illusions such as the Rotating Snakes, and paradoxical images exemplified by the Penrose stairs.