As human beings we interface with the world around us through our senses, like hearing and seeing. Experiments demonstrate that these senses or the way our brains deals with the input is not processed separately. A well known experiment is showing that what we see for instance can override what we hear. This is known as the McGurk effect.

"Seeing" the speaker form the sounds influences our perception of these sounds : when listening to a recording of PA but seeing a clip where the speaker says FA, most test subjects will actually "hear" FA.

The experiment below is even more convincing in how our brain is really the one in the driver seat. Play the clip and look at either of the two buttons. Whichever you look at will be the one you hear!