An optical illusion (also called a visual illusion) is an illusion caused by the visual system 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 percept 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. Pathological visual illusions arise from a pathological exaggeration in physiological visual perception mechanisms causing the aforementioned types of illusions. The aim of this project is to examine different types of illusions in immersive virtual reality. Implementation will be done using a game engine (such as Unity or Unreal). For the immersive virtual reality environments a state-of-the-art head-mounted display (i.e. Oculus Rift or HTC Vive) will be used. User testing will be done using a focus group with minimum of 30 participants using questionnaires and EEG.