These astronomers had the audacity to suggest that the Earth is, in fact, not the center of the universe. Then comes along Nicolaus Copernicus, with Galileo Galilei not far behind. In fact, that makes perfect sense because, when you look at the heavens above, the stars spin and we stay put. You have been taught, like many generations before you, that the Earth is firmly planted in the center of the universe, and all of the stars rotate around us. To demonstrate the impact of top-down processing on scientific discoveries, suppose it is 1473, and you are looking up at the stars. Science is all about discovery, and to make new discoveries we need to make careful observations and find ways to test whether the world is really as it appears to be, according to what are brains are telling us. Given that our brains lie to us on a regular basis, it is important to be open to the possibility that what we see in the world around us is NOT the truth, the whole truth, and nothing but the truth. The STEM Connection One STEM application of top-down processing relates to "the philosophy of science" and the importance of collecting data to help us learn about the world around us. It resolves the discrepancy by giving superiority to the visual information and tweaks what it thinks it hears hence, you hear "fah" instead of "bah" when the lips form the visual cues of "fah." To resolve the difference, the brain has to do something. The McGurk Effect is interesting because the visual information comes into direct conflict with the auditory information. It has to pick out a noise-producing event from the visual system and bind it to the thing that's actually causing the sound. When you think about it, your brain has to do something fairly tricky to pull off this lie. Instead of my trying to explain what it is, take a look at this short video and experience it for yourself (see especially seconds 0:30 - 1:30). įun stuff also starts to happen when the brain attempts to integrate across different senses.Ī McGurk Says What? A really mind-bending demonstration of the integrative power of the brain is called the McGurk Effect. If you didn't know you were looking at your tomatoes in the dark, you would see those plump little fruits as dark red, or even black. ![]() Are they still bright red? Your brain says "yes," but it is lying to you. For example, you know that a vine-ripe tomato is a brilliant shade of red however, when the sun has set, go back outside and look at your tomatoes again. An expectation, or the current context, can completely determine the perceptual experience of an ambiguous stimulus.Īnother great example of top-down processing is to look at something you absolutely know the color of in the broad daylight. We call the brain's influence on perception top-down processing. THE CAT is a nice demonstration of the mind's influence on perception at the level of higher-order symbols (e.g., letters). However, when I put it into context, the perception of it changes completely, depending on what's around it. When I showed you that poorly drawn character out of context, it looked like a crudely assembled set of lines. Notice anything strange about the lettering? The "H" in the first word is exactly the same character as the "A" in second word. Take a look at the lines in the context below. What if I told you it was a letter? Now what do you think it is? ![]() Without moving your eye, move your head closer to your screen until the little person on the right disappears. Close your left eye, and look straight at the cross. Look at the plus sign on the left side if the screen. You might have done this as a kid, but it still blows my mind as an adult. Instead of having a huge blank spot in your field of vision, your brain does some quick acrobatics to fill in the visual scene so it doesn't look choppy or incomplete. It is caused by the junction of a bundle of fibers in the back of the eye called the optic nerve. I'm blind to the fact that I'm blind Did you know you have a huge hole in your vision? It's always there, in both eyes, and it's called the blind spot. ![]() Let's start with a low-level perceptual lie. In this post, we are going to explore some in teresting, and sometimes amusing, ways your brain tricks you by convincing you to let contextual factors guide your perception. Sure, it does all kinds of amazing things, but it also tricks you on a regular basis. To paraphrase the title of a great podcast, your brain is a big, fat, filthy liar.
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