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[DIGITAL EFFECTS] PROFESSOR: Welcome back to 8.701. So we'll start a new chapter now, QCD or quantum chromodynamics. And then, this first lecture of this chapter, we talk about the production of hadrons. This is really meant as an introductory lecture, but we will also already see some very interesting and useful concepts. So we want to produce quarks and anti-quark pairs, and we do this electron-positron collisions. We have studied in detail this first part of the diagram. Specifically, we calculated a cross-section of muon and anti-muon production, and we also have seen more changes than we have same kind of particle in the final state of the electron-positron scattering to electron-positrons. So now, we've replaced the muons with our quarks and anti-quark pairs. And the first step, we want to remind ourselves of the available quarks in this discussion. So we have the up quark, the down quark, charm, strange, top, and bottom. You see that the charges are given h...

[DIGITAL EFFECTS] NANCY KANWISHER: So to remind you, we've been talking last week about doing two things at once-- asking all sort of questions of what we might want to know about face perception in the brain-- there are some questions. But at the same time, the agenda has been to consider the different methods available in human cognitive neuroscience and what kinds of questions each one can answer. So last week, we talked about a bunch of them, and today, we're going to wrap this up talking about TMS and animal studies. But first, I just want to remind you very briefly-- I won't go through in excruciating detail-- we talked about behavioral methods, which are great for characterizing internal representations, as you saw with face inversion effects and some of the other behavioral data, they have major disadvantages, which is that with behavior, you're just measuring the output. It's pretty sparse. And from that, you have to infer all the stuff that h...

[DIGITAL EFFECTS] NANCY KANWISHER: So let's start with one of the deepest questions humans have ever asked themselves. We're not messing around in this class; we're going for it. And one of the deepest questions is, where does knowledge come from? And as you'll know, if you've taken even a teeny bit of philosophy or read even a teeny bit, you know that some of the classic views in Western philosophy-- especially the empiricists, Locke and Hume-- argue that all knowledge comes from experience, right? On the other hand, there are a number of other schools of thought in Western philosophy, of which a dominant figure is Immanuel Kant, who argued that experience alone is not enough. You can't just have experience and figure out all the stuff we have figured out. And so he argued that there has to be what he called "a priori conditions" of cognition, which can't be derived from experience themselves, but have to be given prior to it, OK? So...