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    Biological Influences and Sensory Adaptation

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    Conduct three of the following experiments and record your reactions. Be specific for each experiment.

    1. Rub your index fingers gently over a piece of very coarse sandpaper a few times and rate its coarseness on a scale from 1 (very soft) to 7 (very coarse). After a minute or two, rub the same finger over the paper and again rate its coarseness. Did your perception of the coarseness change? How?

    2. Distribute one cup with sugar water and one with fresh water. Take a sip of the sugar water and swish it around in your mouth for several seconds without swallowing it; gradually, it should taste less sweet. After swallowing it (or spitting it back into the cup), taste from the cup containing fresh water. Did the taste of the fresh water surprise you? How?

    3. Take about 15 index cards and a flashlight that is opaque on all sides (so that light shines only through the front) into a very dark room. After placing all 15 cards over the beam of light, slowly remove the cards one at a time until you can barely detect the light, and then count the number of cards that remain over the light. After a few minutes, the light should begin to look brighter. When this is the case, add a card and see if you can still see the light. Repeat this process of gradually adding cards over a 15-minute period. Were you able to detect an increasingly dim light the longer you spent in the dark?

    4. Fill 3 medium-sized bowls with (a) very hot (but not painfully so) tap water, (b) very cold tap water, and (c) a mixture of the very hot and very cold water. Arrange them, so your right hand is in front of the cold water, your left hand is in front of the hot water, and the lukewarm water is in the middle. Submerse your hands into the water (right into cold, left into hot) for about 3 minutes. After 3 minutes, quickly transfer both hands to the lukewarm (middle) bowl. What did you sense?

    In all four experiments, you will experience Sensory adaptation. Fully describe the process and results of each experiment.
    What is adaptation? Explain adaptation not as just a general dictionary definition. Explain how adaptation is evident in each of your experimental results. Comprehensively describe the sensory systems involved in these experiments, from the receptors all the way into and including the brain. Describe in detail the theories surrounding one of the sensory systems in regards to how we smell, touch, taste, see, etc. Include a discussion on how adaptation is important from an evolutionary perspective.

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    Solution Preview

    1) Rating the sandpaper initially at a 7 for very rough, I found that trying it again a minute later I rated it only about a 4 or 5. The sandpaper still felt rough, but not quite as rough as it did the first time I touched it.

    2) The sugar water does indeed start to taste less sweet. After the sugar water, the plain tap water seems to have a distinctly bitter and metallic flavor.

    3) The longer you are in the dark, the more light you can see even with the cards over the flashlight. By the time you have been in the dark the entire 15 min. or so, you can see the light even with most of the cards still covering it, which was not the case when the experiment began.

    4) The hand that was in the hot water feels the warm water as being cool. The hand that was in the cold water feels the warm water as being nice and warm. After a minute, both hands feel the water as being the same temperature.

    All these experiments demonstrate sensory adaptation. In the first experiment, the touch receptors on the skin are very sensitive when they come into contact with the rough sandpaper. The second time, however, some of the nerves in the skin that perceive touch are still desensitized after firing the first time. Because not as many touch receptors are firing their signals to the brain the second time, the brain perceives that the paper is not as rough. In the second experiment, it is receptors on the tongue (taste buds) that are affected. There are several different types of taste buds, and each type is sensitive to only one flavor: sweet, salty, bitter, and sour. Normally when we drink water, the brain perceives it as not having much of a flavor. When you have sugar water in your mouth for a while, the receptors that detect sweetness at first become very active, sending lots of "sweet" signals to the brain. After a while, though, the receptors are unable to fire anymore, and your brain stops tasting the sweetness. Now when you take a drink of ordinary water, your brain is not getting any sweet signals at all, so instead it notices the other tastes, such as bitterness, because those receptors are still active. In the third experiment, it's the receptors in the eyes that are affected. In normal light, the receptors in our eyes called cones are active. These see color very well. In normal light the rods are not active, because they are very sensitive to light. When you walk out of a dark movie theater, the light seems very bright at first, because all of the rods and cones are firing. After a minute, the light starts to seem less bright. This is because the rods have been stimulated so much that they cannot fire anymore. When you are in the dark room playing with cards over the flashlight, you are giving the rods time to recover. Because they are much more sensitive to low light than the cones, once they are active in the dark you can see much better with less light. The hands in warm and cold water are responding to changes in the nerves that sense temperature ...

    Solution Summary

    This solution discusses the three experiments in 2052 words.