Yesterday I saw this BBC video about the McGurk effect. Basically, it’s a phenomenon where your brain interprets sounds differently based on what you are seeing. It’s a really amazing and robust effect, especially since it is not dependent on you not knowing about it.
This reminds me a lot of when I was teaching undergraduate physics labs and we would do the famous ball drop experiment where you would release two balls (same size but different mass) from the same height and see which one hits the ground first. The majority of these intro students would usually predict that the more massive ball would hit the ground first (a common intuition to have). The interesting thing was that a few of these students would still think this after we had done the experiment.
I remember asking some of them why they still thought that the more massive ball hit the ground first. And inevitably, some of them would say, “I heard it hit first.” At the time, this seemed kind of crazy to me because I had been there and heard the two balls hit at the same time and other people in their group had also heard them hit together. But they insisted that they heard a separation.
Later when I started studying science education I learned the name for this phenomenon: theory-laden observations. The students thought that the more massive ball would hit first and this influenced how they took in information and therefore their observation confirmed this idea. However, it seems possible that it might be even more complicated than that. Although the McGurk effect seems primarily to be focused on hearing different phonemes and sounds based on lip movements, it’s possible that the parts of the brain being confused in that area are the same as the ball-drop phenomenon. Students *think* they see the massive ball hit first and therefore *hear* it hit first.
(via kottke)
Cynthia D'Angelo 
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