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Bottom-up vs. top-down processing

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Voiceover: Let's look at the difference between top-down and bottom-up processing. So, what is bottom-up processing? Bottom-up processing basically begins with the stimulus, so let's imagine that we're looking at something, or let's say I'm looking at a banana. The banana is sitting there and it influences what we perceive. So, stimulus influences what we perceive, our perception. So, if I know absolutely nothing about something, then the stimulus or whatever it is I'm looking at, yet I don't know anything about, I've never seen it, I don't have any preconceived cognitive constructs about what it is I'm looking at. The stimulus basically is influencing my perception. So, for example let's imagine that I'm looking at a cockpit of a plane. I'm not a pilot, so I'm not really too familiar with everything and everything kinda looks fairly confusing. So, basically all the different stimuli, so this stimulus, a bunch of gauges, and this rudder-looking thing, I'm basically looking at all the different little parts of something that is new and novel to me, and trying to kind of comprehend what it is I'm looking at. So, this is bottom-up. This is when you start with no preconceived idea of what it is that you're looking at, and allow the stimulus to influence your perception of what it is that you're looking at. So, bottom-up processing is data-driven, and your perception of what it is that you're looking at directs your cognitive awareness of the object. So, in contrast, top-down processing basically uses your background knowledge, so uses your background knowledge to influence perception. So, let's look at this example over here. So, what we're actually seeing are a bunch of circles, they are just a bunch of circles and then inside the circle there are a couple of lines drawn. So, we are looking at this set of circles, these white circles with lines drawn inside of them. We are creating this cube. We're basically taking these lines and then putting them together in order to create a cube. Even though the stimulus itself, which is the circles with the lines, actually doesn't draw a cube because there are these black spaces over here, and there is absolutely nothing in the black spaces, but our brains are basically taking this information and using our knowledge of cubes and what they're supposed to look like, we're recreating a cube despite a lack of a cube actually being present in the image. So, that's top-down processing. It's using your background information, your background knowledge, your learning, your expectations, in order to influence what it is that we're perceiving. So, in other words, it's theory-driven. We look at this and we assume that they're trying to represent a cube, even though one's not actually drawn there, and we're using that theory in order to shape our cognitive understanding of what it is that we're looking at. So, our perception, our behavior is influenced by our expectations, which is top-down processing. So, we're using what's already in our heads in order to perceive what it is that we're looking at, whereas in bottom-up processing we're using the stimulus itself in order to drive our perception. So, another good example of top-down processing would be "Where's Waldo?" So, in "Where's Waldo?", we have a mental idea of what we're trying to do, which is to find Waldo amidst this really jumbled mess of a picture. So, if we were using bottom-up processing in order to look at this we would just be seeing a whole bunch of little people, and we wouldn't really be goal-driven, we wouldn't be trying to do anything, but with top-down processing we have a goal, and we're able to look through here to find Waldo.