What Is Sensory Adaptation?
Human beings have five primary senses: sight, sound, smell, taste and touch. When we step into a hot tub filled with water at 102 to 104 degrees Fahrenheit, we initially feel that the water is terribly hot. This is what we sense. When a little time has passed, and our body has adjusted to the hot water, it feels comfortable---even soothing. The temperature has remained constant---this is the experience of sensory adaptation.
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Definitions and Example
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The relevant definition (according to Websters New Universal Unabridged Dictionary) of "sensory" is an adjective meaning 1. of the senses or sensation 2. connected with the reception and transmission of sense impressions. "Adaptation" is a noun meaning adapting or being adapted.
Consider the subject of "background noise." We hear (or are connected with) the sound of a room air conditioner or the low hum of a refrigerator when we enter the room or the kitchen. In a short time, those sounds fade into the background, and we no longer consciously hear them. Our sense of hearing has adapted to it.
Sense of Sight
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We're walking in the forest on a moonless night. The first vision change is immediate: enlargement of the pupil. This permits more available light to enter the eye, stimulating the retina. The retina is the part of the eye that senses light. It's comprised of two types of cells called rods and cones. Rods perceive low levels of light and are our night-vision receptors. Cones perceive color and detail. Both cells contain a light-sensitive chemical.
So, while walking in this dark forest, the cones quickly adapt to the darkness and do not respond to any light levels present. No color vision exists in this circumstance. Meanwhile, the light concentration of rods increases in this scenario, and they become fully adapted to the dark within half an hour.
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Sense of Sound
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When listening to the loud music of a heavy metal band, the tensor tympani and stapedius tensor muscles in the middle ear contract. This action minimizes transmission of sound vibrations to our inner ear. The inner ear is where these vibrations are detected. This is a reflex thought to be a protective mechanism to shield the inner ear from harm. Although when the music starts, it seems loud, soon sensory adaptation occurs, and we no longer consider the volume too high.
Sense of Smell
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Before you left for work this morning, you prepared the ingredients for beef stew and placed them in the slow cooker. For several hours the meat and vegetables have been slowly cooking. When you return home in the evening, you welcome the aroma. Entering the kitchen, you preheat the oven for biscuits and prepare a salad. Before long, without realizing it, you no longer detect the smell of the stew. Your sense of smell has adapted.
Sense of Taste
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The taste buds of adults are located on the tongue. There are thousands of tiny taste buds that detect four basic taste types: sour, sweet, salty and bitter. The sour taste buds are located on the sides of the tongue. The sweet and salty taste buds are on the front of the tongue, while the bitter taste buds are on the back of the tongue. Very few taste buds are found in the center of the tongue. When you're eating, the saliva in your mouth breaks down the food. "Receptor cells" in the taste buds send messages to your brain through sensory nerves. This process allows your brain to detect and advise the flavor.
When you begin sucking on a cherry Lifesaver, the sweet and sourness of the cherry flavor is distinct. Before it has fully dissolved in your mouth, sensory adaptation has occurred, and the flavor is not nearly as distinct.
Sense of Touch
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Our sense of touch springs from nerve endings found in the bottom layer of our skin called the dermis. These nerve endings send messages to our spinal cord, which transmits the information to our brain. This is where feeling is recognized. We have about twenty different nerve endings in the human body, with the most common receptors being hot, cold, pressure, pain and touch.
When we dive into a swimming pool in the extreme heat of an August afternoon, the water in the pool feels cold. Within a short period of time, though, sensory adaptation takes place; and the water feels quite comfortable.
Sensory Adaptation: Balance
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Sensory adaptation permits a living creature (human, animal, plant, microorganism) to find balance with its surroundings and efficiently respond to changes in stimuli. Many theories exist and studies continue to evaluate this phenomenon in organisms of all kinds.
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