[MUSIC]. Okay, so let's listen to an audio illusion. First we're going to listen to the first tone Marion. [SOUND] Okay. Now the next tone is it higher or lower? [SOUND]. So Marlon tells me it sounds lower, I trust him, I'm a little on the tone death side. But remarkably this is the first tone here, and this is the second tone. The second tone is actually so each of these lines is frequencies that are contained in the stimulus. And you can see that the second tone actually consists of higher frequencies, starts higher. But what's actually happening here is that we are assigning this group of frequency, frequencies to its fundamental frequency, which is down here. What you're seeing here are the fundamental, plus the harmonics. [SOUND] So in the case of the first tone, it was 250 hertz, plus harmonics at 500, 750, 1000, and 1250 hertz. This is close to middle c. In the second tone, what this is, this is 225. But we didn't play 225. We played 450, 575, 800, and 1,025. We assigned this group to that to this frequency, 225. We heard something that wasn't in the stimulus. And in the final one. Let's see whether this one sounds more like the first, [SOUND] or more like the second. [SOUND] One more time. [SOUND] So that one, sounds more like the first tone. And what that is is it's, it's just playing these four frequencies. You're doing the same thing that you did here. You're assigning it to this tone. You're assigning it to a frequency that is not in the stimulus. So this is another example of an illusion. Just remember that perception is entirely about interpretation. We're going to look at one more example. [MUSIC]