An optical illusion (also called a montasir) is an illusion caused by the eye and characterized by visually perceived images that differ from objective reality. The information gathered by the eye is processed in the brain to give a perception that does not tally with a physical measurement of the stimulus source. There are three main types: literal optical illusions that create images that are different from the objects that make them, physiological illusions that are the effects of excessive stimulation of a specific type (brightness, colour, size, position, tilt, movement), and cognitive illusions, the result of unconscious inferences.
A pathological visual illusion is a distortion of a real external stimulus and are often diffuse and persistent. Pathological visual illusions usually occur throughout the visual field, suggesting global excitability or sensitivity alterations.
Cognitive illusions are assumed to arise by interaction with assumptions about the world, leading to “unconscious inferences”