So in this first module we're going to be talking about things that we need as a background for the course. I'm going to begin by trying to get you involved in the mysteries of vision, by telling you a little bit about what we actually see and describing the peculiarities of that. So let's begin with some basic definitions, and the first one is perception. I already said perception is what we are aware of, so that's about as good as it gets. If you want to define perception in terms of vision, it's what when we look out at the world, we're actually aware of seeing. And you might ask well, what about you're not focused on that, and you're seeing stuff but you're not really aware of it? Yeah that's true. And the same kinds of mechanisms and strategies apply, but basically when we're talking about perception, we're talking about what we see and, generally speaking, we're aware of what we see. Or at least we can be. That's very different than physical measurements. So you can make physical measurements of the world that's out there with instruments. They can be simple, they can be complex. You can use a ruler, a protractor, something like the photometers in your smart phones. Or much more complicated instruments but basically these are physical measurements that physicists and business scientists have been making for a long, long time. That's quite distinct from psychophysical measurements, measuring what we actually see and there is really no way because that is subjective. Physical measurements, of course, objective, but what we see is subjective. There's no real way of measuring that in the same sense. But, nonetheless, it can be made with measurements that are comparative measurements. So, this is a strategy that was undertaken first in the 19th century by German vision scientists and psychologist of that era. And basically you can understand what you're seeing and measure it in a very good way, but not in the same objective way that we measure angles and line lengths, and so on, you can do that by making comparative measurements. You take a standard stimulus and you ask somebody to adjust another stimulus until the two match. And in those kinds of ways and there are different ways of doing that. We'll talk about some of them as we go along. In that way you can make psychophysical measurements that are pretty useful. But they're not the same as physical measurements and you need to understand that.
