The McGurk Effect

The McGurk Effect is an interesting phenomenon that shows how hearing and vision work together to aid our perception of speech. The effect occurs when a audio component of one sound is paired with the visuals of another sound. This tricks our ears into hearing different sounds depending on what we see. The Effect is named after Harry McGurk who discovered the phenomenon in 1976. Interesting enough, many factors affect whether you can perceive this effect, such as damage to the brain, gender, speech and language disorders, visual distractors, schizophrenia, autism, and more. The effect even works if you're aware that it's happening, demonstrating how powerful it is. See the McGurk effect in action here:

To learn more:
http://mentalfloss.com/article/72587/mcgurk-effect-or-brains-are-weird