McGurk Effect

What is the McGurk Effect?

The McGurk effect is a perceptual phenomenon that demonstrates an interaction between hearing and vision in speech perception. When auditory and visual speech signals conflict, the visual information can alter what we perceive auditorily. It was first described by Harry McGurk and John MacDonald in 1976.

The original study (McGurk & MacDonald, 1976)

McGurk and MacDonald reported the effect in 'Hearing lips and seeing voices' (Nature, 1976). In their stimuli, a recurring auditory syllable was dubbed onto a video of a face articulating a different syllable. When the sound ba was paired with a visible ga, most adult listeners reported hearing da — a fusion that matched neither input. Notably, the illusion persists even when listeners know exactly how it is constructed, which is part of what makes it scientifically interesting.

Why it happens

Speech perception is multimodal: viewers routinely use visible articulation — lip, tongue, and jaw movements — to disambiguate what is being said, especially in noise. When visual and auditory streams conflict, the brain integrates them rather than simply picking one, yielding a percept that matches neither stream. Susceptibility varies across individuals and languages, and the effect weakens or disappears with mismatched voices, avatars, or poorly synchronized video.

Where it shows up

Audiovisual speech integration matters well beyond the lab: understanding conversation in noisy rooms, dubbing and lip-sync in film, fitting of hearing aids and cochlear implants, laggy audio on video calls, and the design of virtual avatars. Perception degrades quickly when the streams drift out of sync — one reason broadcasting maintains strict lip-sync standards.

About the demo on this page

This page offers an audio-only syllable player and a static illustration. It cannot reproduce the McGurk effect, because the effect depends on watching a face articulate a syllable. The illustration is not a trial and produces no result; it simply shows how the classic conflicting stimulus is constructed.