Illusion 4 -- The Eye Is Mightier Than the Ear

The last optical illusion posted on this blog was Optical-Illusion 3 -- 18th-Century FX. This new post is also an optical illusion, but it's combined with an audio illusion. Therefore, let's call it an audical illusion. Here's how it works:

Play the video below. It lasts only 7 seconds. As you watch the video, listen very closely to what the man is saying. What do you hear? You hear "FA, FA, FA." Right?

You are very wrong. To prove it, play the video again, this time listening with your eyes shut. What do you hear? You hear "BA, BA, BA." Right? Don't trust me? Think it's a trick? Fine. Continue to replay the video how often as you like; each time, the sound will change based on whether or not you are also watching the video.

How is this possible? It is caused by the McGurk Effect, first described in 1976. In simple terms, it states that we are "trained" to receive visual clues to help us hear and understand human speech. It also implies that our sense of sight is more powerful than our sense of hearing. Therefore, when the sight and sound conflict, sight usually wins. This strong sense of sight is also noticeable when it conflicts with our sense of taste -- Crystal Pepsi and Tab Clear, colorless cola drinks sold in 1992-1994, failed because many users could not "taste" the cola without the familiar brown liquid color. This also explains the prevalence of food coloring in many foods and drinks.