Optical Wonderful
Illusion Category
Sound Illusions
A bonus category: illusions that trick the ear and brain the way visual illusions trick the eye, from speech perception quirks to tones that seem to rise forever.
Auditory
McGurk Effect (Audio-Visual Illusion)
Dub the audio 'ba' over video of a mouth silently saying 'ga,' and most listeners hear neither - they hear 'da,' a third sound their brain invents by fusing mismatched ears and eyes.
AuditoryShepard Tone (Auditory Barber Pole)
A tone that seems to climb in pitch forever without ever actually getting any higher - the auditory equivalent of an Escher staircase that always ascends and never arrives.