[MUSIC] So the last lesson today concerns auditory objects and scenes. We've been talking as if we hear pitch, we hear loudness, we hear timbre, but of course we don't think of what we hear in those terms of all. We hear footsteps approaching. We hear a creaking door. We hear rain on the roof and so on and so forth. We hear things as auditory objects. We don't hear them, we can think about them and dissect them and retrospectively hear them as what was the pitch of the creaking door, etc. But what we hear as objects, and those objects are put into a scene, again by sort of analogy with sort of a visual scene. And this is another important aspect of the kinds of things that we're going to be discussing and worrying about as we go forward in the course. Because very importantly, we can track and do track the components of an auditory scene. So we listen to the footsteps approaching the door. We anticipate that the door is going to be open, we hear it open. And this is the way our auditory behavior actually operates. We track the footsteps, we track what's happening. We use it for the advantages we glean from the ability to track a series of sounds into something that has meaningful information with respect to what behavior should we carry out next. So this also pertains in music. Let's go back to the Twinkle Twinkle Little Star that we heard Marie perform earlier with Mozart's 9th variation. If you play a little melody like that and you play it together at the same time with another familiar harmony, like Mary had a Little Lamb. So, your playing these two melodies at the same time, you easily distinguish them if the pitches are relatively far apart, even though they're in the same key. If these are an octave apart, you can easily distinguish the two tones. But as you bring the pitches closer together as in the upper panel here, what happens is you begin to confuse them, and the demonstration that you're going to hear now is just showing you this. The easy distinction when they're played with a pitch relatively far apart, and the difficulty you have tracking when the sound signal is brought closer together in the two melodies. [MUSIC] So let me just end by going over the main points of the module today. The first of these is that the perception of sound stimuli is described in terms of three basic qualities that you'll certainly want to keep in mind as we go forward, loudness, pitch, and timbre. And these are related respectively to the intensity of sounds, the frequency of sounds, and a variety of qualities of sounds signals when the intensity and frequency are the same. Second point is these subjective qualities are not related to objective physics, to sound signals, in any simple way. I think I've gone over that and drummed it into you again and again. And the third point is that the evidence for this comes from a variety of musical and non-musical observations, and I think they are equally important and impressive. And, finally, that a major challenge in audition is to explain the odd relationship between the objective and this subjective fact that again is going to come back and be featured as we go forward and talk about all of this more and more in the context of music and aesthetics. So just to give you an idea of what's coming next, we're going to be talking about in the coming module. A vocalization and all, it's a complicated issue, and I'll introduce you to vocalization and it's important in understanding music.