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The rate of coarseness during the initial rub was seven, on a scale of 1-7, depicting a very rough surface. On the second rubbing attempt however, the perception of coarseness reduces to the rate of four on a scale of 1-7.
The sugar water leaves a ‘normal’ feeling of sweetness. The mouth environment changes and adapts the ‘normal’ feeling of sugar water. Introduction of fresh water however, changes the taste and one can easily feel the distinct ‘salty’ taste of fresh water. The fresh water introduces a completely different unique salty taste whose concentration wanes after a few seconds.
There is a notable change of temperature when both hands are introduced into the lukewarm bowl of water. The hand from the cold bowl of water feels the most distinct difference. The warm feeling is a bit pronounced but the hand quickly gets accustomed to the lukewarm feeling. Though a bit diminished, the hand from the hot bowl experiences reduced temperature as the lukewarm feeling takes effect. In fact, the hand from hot water feels cold when introduced to lukewarm water. After a while both hands get accustomed to the lukewarm effect and distinct feeling initially diminishes.
Sensory adaptation is also referred to as neural adaptation and involves the change in responsiveness of the sensory system in reaction of a constant or continual stimulus (Coon, 2010, p. 150). Sensory adaptation is normally felt as change in the stimulus. For instance when a person comes into contact with a new surface texture, he/she feels the surface’s texture on the skin. After sometime, usually minutes, the person stops feeling the surface texture.
This concept is referred to as neural or sensory adaptation, where sensory neurons are initially stimulated by the surface’s texture and they respond immediately (Nevid, 2012, p. 94). After a while however, the level of response reduces as few neurons are released. In essence, sensory adaptation connotes the temporary change in neural response to stimulus because of preceding or previous stimulus.
In the experiments performed above, adaptation comes out clearly. As mentioned earlier, adaptation takes place as result of repeated stimuli that gradually diminishes the response of sensory neurons. In the first experiment, initial rubbing of the thumb on the sandpaper produces a distinctive feeling of coarseness. Repeated rubbing reduces the response of sensory neurons hence the finger adapts to the feeling, thus, producing the feeling of reduced coarseness. In the second experiment, the mouth adapts to a unique sugar taste from the sugary water thanks to reduced response of sensory neurons on the tongue.
However, fresh water introduces new stimuli into the mouth environment thus erasing the feeling of distinct adaptation from the mouth. In experiment four, both hands distinctly feel the different state of lukewarm water. The hand from cold water feels hot when in lukewarm water because it had adapted to cold water. The hand from hot water feels a bit cold because it had adapted to the hot water. After sometime however, the unique lukewarm feeling becomes dominant as both hands adapt to the different temperature.
Sensory systems involved in the experiment
In experiment 1, the tactile sense explains the adaptation felt. When rubbing took place, information was carried from skin receptors to numerous neuronal axons which are part of the somatosensory cortex on the top of the brain surface. Cell bodies of the central nervous system on the somatosensory cortex receive the information from the skin which collectively may be referred to as sensory input (Coon & Mitterer, 2008, p. 142). Sensory input is channeled to the central nervous system neurons. The somatosensory cortex in turn sends sensory input messages to the brain.
In experiment 2, epithelial taste cells on the tongue function as receptor cells. Dissolved polar molecules, in this case sugar are transported to the taste pores, transducting chemical stimuli into nerve impulses. Binding of polar molecules with receptors pair with gustaducin that lead to a discharge of neurotransmitters effectively generating efferent nerve ending (Nevid, 2012, p. 96). Interaction between receptors and electrolytes lead to stimulation taste buds on the tongue generating a neural code that is decided by the central nervous system and repeats the process described in experiment one above.
In experiment 4 temperature receptors lying under the skin are stimulated by hot or cold environments triggering neurons to the somatosensory cortex on top of the brain surface. Central nervous system cells then receive the temperature sensory input (Nevid, 2012, p. 98). The somatosensory cortex then sends input messages to the brain.
In all the experiments above, a large number of neurons sent initially make the initial feeling overwhelming. However, the number of neurons sent through the central nervous system reduces gradually, effectively reducing messages sent by the somatosensory cortex to the brain thus leading to adaptation.
Adaptation and evolution
Adaptation is one of the most important concepts in evolution. According to Ridley (2009, p. 45) adaptation refers to the ability of organisms changing to suit the prevailing dynamic environmental conditions for survival. Adaptation mainly determines the fitness and survival of an organism in the environment. Adaptation therefore means technically ‘getting used’ to the environment by organisms for the sole purpose of survival.
Coon, D. (2010). Psychology: A Journey. New York: McGraw-Hill.
Coon, D. & Mitterer, J. (2008). Introduction to Psychology: Gateways to Mind and Behavior. New York: Willey & Sons.
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Nevid, J. (2012). Psychology: Concepts and Applications. New York: Cengage Learning.
Ridley, M. (2009). Evolution. New York: Routledge.