Apparent rotation and jazzing in Leviant's Enigma illusion

Area of Science:

• Visual Perception
• Neuroscience
• Psychophysics

Background:

• The Enigma figure creates an illusion of rotary motion without actual movement.
• Previous theories suggested accommodative fluctuations and eye movements, or involvement of visual area V5.
• No definitive explanation for the Enigma illusion existed prior to this study.

Purpose of the Study:

• To investigate the underlying mechanisms of the Enigma illusion.
• To determine the role of accommodation and eye movements in the Enigma illusion.
• To explore the conditions under which the Enigma illusion is perceived.

Main Methods:

• The Enigma figure was presented with variations in color, accommodation (using cycloplegic lens and pinhole), and eye movements (using after-images).
• The orientation and form of the inducing lines were manipulated.
• Perceptual judgments of rotary motion were recorded.

Main Results:

• The Enigma illusion persists despite the elimination of accommodation changes and eye movements.
• The illusion is perceived with both colored and achromatic annuli.
• Apparent rotation is strongest when inducing lines are perpendicular to the annulus, but is still perceived with other configurations.

Conclusions:

• The Enigma illusion is not caused by accommodative fluctuations or eye movements.
• A neural mechanism is proposed where lines abutting an empty annulus elicit orthogonal streaming motion.
• This mechanism explains the perception of rotary motion in the Enigma figure.