Dub the sound 'ba' onto a video of a mouth saying 'ga' and many people hear a third syllable, 'da'. It is called the McGurk effect, and it shows the brain blending sight and sound before we are aware of either.
AI-generated image, not a photograph of a real person or place.
ba + ga heard as da
Eyes and ears blend
People vary widely
Stable over years
An illusion you can hear
THE SHORT ANSWER
When sight and sound disagree, they blend.
First described in 1976. Still a standard test of how we combine the senses.
THE ILLUSION
Ba plus ga makes da
Pair an auditory syllable with a different visual one and people often hear a third syllable, different from both. Hearing 'ba' while seeing 'ga' is the classic example.
Pick a pairing of sound and lip movement. The bar shows how strongly the lips tend to change what is heard.
Based on McGurk-effect studies published in PubMed Central and the summary in Wikipedia. Responses vary a great deal from person to person.
TWO NUMBERS WORTH KNOWING
Huge differences between people.
One finding on individuals, one on languages and cultures.
0–100%
How often individuals heard the illusion
Some participants never perceived it and others always did. For single stimuli, 77% of people almost never (10% or less) or almost always (90% or more) heard it.
INDIVIDUALS · 165 ADULTS, 12 STIMULI
48 · 44%
Mandarin vs English speakers
Averaged across people and stimuli, Chinese and American participants heard the illusion about equally often. Culture and language explained only 0.3% of the variation.
LANGUAGES · 307 ADULTS
A study of 324 Mandarin-speaking twins found twins were more alike than unrelated pairs, but shared genes and environment explained only a small part (5.5%) of the variation.
MAKE YOUR OWN TEST
Dub a sound, watch what happens.
The effect was found by accident when a video was dubbed with a different syllable. You can recreate it with a phone and a free video editor.
Film a mouth saying 'ga'
Record a friend's face, close up, slowly repeating 'ga, ga'.
Dub 'ba' over it
Record 'ba, ba' at the same pace and line it up with the lip movements in the editor.
Watch, then close your eyes
Many viewers hear 'da' while watching. With eyes closed, only the recorded 'ba' is left.
Compare with friends
Expect disagreement: in studies some people always hear the illusion and some never do.
AI-generated image, not a photograph of a real person or place.
WHY IT MATTERS
A stable trait, not a party trick.
AI-generated image, not a photograph of a real person or place.
Researchers use the McGurk effect to study how the brain combines sight and sound. People are remarkably consistent: retested a year later, their rates changed by only 2% on average.
Knowing about the illusion does not seem to switch it off; some researchers who have studied it for decades still experience it. The original 1976 recordings are lost, so each laboratory makes its own, which is one reason results differ between studies.
Questions
Questions people ask
What is the McGurk effect?
An illusion in which pairing one spoken sound with lip movements for a different sound makes people hear a third sound. Hearing 'ba' while seeing 'ga' often produces 'da'.
Who discovered it?
Harry McGurk and John MacDonald described it in the journal Nature in 1976, in a paper titled 'Hearing lips and seeing voices'. It was found by accident when a video was dubbed with a different syllable.
Does everyone experience it?
No. In studies, some people never perceive the illusion and others always do, and different recordings also vary in how strongly they produce it.
Is it stronger in some languages?
A study of 307 adults found similar rates in native Mandarin and American English speakers (48% and 44%), with culture and language explaining only 0.3% of the differences.
Can you stop hearing it once you know?
Generally not. The effect is described as very robust: knowing how it works seems to have little effect on whether you perceive it.
