Optical illusion

An optical illusion is a visual experience in which an object or scene appears different from its physical properties or arrangement. It arises from how visual systems interpret sensory information.

Visual perception: The processes by which the brain interprets information received from the eyes. Illusions reveal the rules and assumptions that shape ordinary visual perception.
Checker shadow illusion: An image illusion in which two equally shaded squares appear different because one lies in a depicted shadow. It demonstrates how inferred illumination changes perceived surface lightness.
Visual system: The neural pathways and structures that process visual information from the eyes. Illusions arise through interactions among these pathways, not solely at the eye.
Optical phenomenon: An observable effect produced by the behavior of light, such as reflection, refraction, or diffraction. A physical optical effect changes light itself, while an illusion concerns perceived appearance.
Psychophysics: The study of relationships between physical stimuli and the sensations and perceptions they produce. Researchers use controlled illusions to measure how stimulus properties shape perception.
Gestalt psychology: A psychological approach emphasizing how people perceive organized wholes rather than isolated sensory elements. Gestalt grouping principles explain why arrangements of lines and shapes can mislead.
Café wall illusion: A geometric illusion in which parallel horizontal lines appear slanted between offset rows of contrasting tiles. Its tiled pattern makes straight, parallel boundaries seem to converge or diverge.
Retina: The light-sensitive tissue at the back of the eye that converts light into neural signals. Some visual effects begin with adaptation and interactions among retinal cells.
Visual hallucination: A visual experience of something that is not present, occurring without a corresponding external stimulus. Hallucinations lack the external image that ordinarily drives an optical illusion.
Experimental psychology: The scientific study of behavior and mental processes using controlled experiments. Illusions provide reproducible tests of perceptual mechanisms and their limits.

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