The McGurk effect is a concept that scientists have studied over the years to determine how our bodies perceive a sound that is being mouthed in front of us versus one being verbally said behind us. In other words, if an individual were to say the syllable ba behind us and then an individual were to mouth ga in front of us our brains would not perceive either of them. Our brains typically will find the middle ground between what we are seeing and hearing. In the instance above our brains would combine the two with a result of da.
With this perceptual phenomenon of speech perception, our brains are forming a third sound from the sound we are physically hearing and one that we are seeing. This concept has been studied and has shown it is more than just a multisensory perception. It is an automatic and unconscious response that happens when our visual and speech senses emerge together. This leads to a deeper understanding of the type of facial information that is required for visual speech perception. The McGurk effect has also been proven to work with different genders, recognizable faces and voices, and different languages making it a diverse illusion.
sources: See What I'm Saying
Photo source: https://kids.frontiersin.org/articles/10.3389/frym.2022.705956