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Voiceover: In this video we're going to talk about something known as sensory adaptation. Sensory adaptation. As the name implies what sensory adaptation is is a change in the sensitivity of your perception of a sensation. We're going to look at a couple of different examples of sensory adaptation. The first example, the first sense that we're going to look at is hearing, your sense of hearing. Let's look at hearing. How is it that we're able to go to a rock concert and listen to the entire concert and walk out and still be able to hear things? How is it that our ear drums aren't blown out because of the really really loud sound? One of the ways that you're able to adapt to really loud noises is by a small muscle in your inner ear. What this inner ear muscle does is whenever there's a really loud noise it causes it to contract. When the muscle contracts it actually dampens the vibrations that go into your inner ear. By dampening really loud noises it actually helps protect your ear drums from getting blown. It helps protect your inner ear from getting damaged. This actually takes a few seconds for it to kick in. It doesn't work for really really immediate super loud noises such that of a gunshot or a rifle fire. The rife, when it goes off, the noise occurs really really quickly. The muscle doesn't have time to contract and protect your ear. You can actually have some kind of damage if you do hear a gunshot close to your ear because of this inability to contract very quickly. Another sense that we rely on heavily and that is adaptable is our sense of touch. You might've noticed that if you dip your hands in really cold water it's super cold at first, but over time the water doesn't feel as cold. That's because the sensory nerves in your hand that are sensitive to temperature, as soon as they go off, they become saturated. They stop firing as much. Your sense of touch, your sense of temperature gets adapted. Another sense that is adaptable is your sense of smell. We can detect really really low concentrations of chemicals in the air such as perfumes. I don't know if you've ever actually experienced this or not, but if you spray some cologne or some perfume on, over time at first you're able to smell it. Over time you forget that you're wearing it. That's again because the sensory receptors in your [ear], they become desensitized. They become desensitized to the molecules. Similarly, your sense of touch, the temperature receptors also get desensitized. There are a couple of other senses that also get-- that can also change and adapt to changes in stimulus. One of those changes is your sense of proprioception. This we talked about in an earlier video, but is your sense of balance, your sense of self, knowing where you are in space. One experiment they actually did to change someone's sensation of proprioception was they actually put some goggles. Imagine here we have a person. Here are his eyes. What they actually did was they put goggles on. What these goggles basically did is they skewed everything. They either made everything upside down or they titled everything at a certain angle. Basically, the perception of the world basically changed. What they were seeing was no longer what they were used to. Over time, their brain was actually able to accommodate. If an image was initially upside down, over time, the image got flipped right side up again. There's this sensory adaptation that can occur for your sense of proprioception as well. Another sense that undergoes sensory adaptation is your sense of sight. For all these senses over here we were talking about down regulation. Hearing, whenever it's a really loud sound, the muscle contracts and your ability to perceive sound is down regulated. This is the same with touch. Over time your ability to feel certain things, feel pressure, feel temperature gets down regulated. The same thing goes for smell and proprioception. With sight, we can get both down and up regulation. We can get both down and up regulation. When would we get down regulation? Imagine that it's really really bright outside. If it's super bright outside, you've got lots and lots of light coming in and it enters your eye. If your pupils were really big and dilated, let's imagine that you've got your pupils here and they're really big and dilated. A whole bunch of light would enter your pupils. In fact it could even damage your retina. One adaptation that your eyeball has to really bright intensity light is the pupil actually constricts. The pupil gets smaller. It goes from this size, for example, to this size. What that effectively does is it allows less light to enter the back of the eye. Another adaptation to bright light that occurs in your eye is the change in the sensitivity of your rods and cones. There's an entire playlist on site in which I talk about rods and cones. Basically what occurs is your rods and cones that are sitting in the [ren] in the back of your eye, they get desensitized. They actually lose sensitivity to light over time. The combination of pupil constriction and desensitization of the rods and cones in your eyes effectively leads to a down regulation in your ability to sense light. What happens in a dark setting? In a dark setting when there's not a lot of light, there's not very much light. We can just draw a little bit of light coming in. What you'd want to do is the exact opposite. If your pupils were initially small, you'd want to make them big so that we can get more light coming into the back of the eye. In addition, what happens in the dark is these rods and cones actually start synthesizing light sensitive molecules. There's actually more light sensitive molocules. They become more sensitive to light. This effectively leads to a up regulation in sensitivity.