Sensory adaptation refers to the way a human body reacts and adjusts to constant stimuli by using diminished sensitivity. In this article, we will look at why this phenomenon occurs, its function and significance, and a few examples to help understand it better.
Large type 1 nerve cells used for the sense of touch show sensory adaptation, but the smaller type 4 nerve cells used for sensing pain do not. Therefore, pain stays for a long period of time, while the sense of touch loses sensitivity if stimuli in the surroundings remain constant.
Sensory adaptation, also known as neural adaptation, is defined as the diminished sensitivity to a stimulus as a consequence of constant exposure to that stimulus. It can be explained as the reaction of the brain cells which fire whenever the sensory organs of the body pick up a new stimulus. However, if the stimulus does not change in the environment, sensory adaptation occurs, and the firing of the brain cells reduces significantly in response. This means that, eventually, the person changes his/her level of sensitivity, and stops paying attention to the unchanged stimulus. Let’s look at why sensory adaptation is so important.
Function of Sensory Adaptation
Sensory adaptation occurs both, in the short term and long term. The changes in the muscles of the legs and arms when walking on different types of terrain is an example of short-term sensory adaptation. Breathing movements by the lungs are also affected by sensory adaptation. This allows us to put aside the unpleasant or repetitive environment, and focus on a task that we desire to work on. Thus, sensory adaptation is an essential part of every person’s daily life, and is important in terms of evolution, by developing beneficial characteristics and passing these genes on to the next generation.
Sensory Adaptation in Psychology
In cognitive neuropsychology, transcranial magnetic stimulation (TMS) is an important tool for researchers to investigate short-term interference on neural processing. The result of these studies shows that the visual cortex of a person is influenced by TMS; they can see flashes of colorless light. However, when the TMS was used to constantly stimulate the brain into viewing flashes of light of a particular color, sensory adaptation occurred. So, when the original stimulus was used, the flashes of light now came in the same color as the constant stimulation.
Examples of Neural Adaptation
Sound Sensory Adaptation: If a person is sitting in a room with an air conditioner that is constantly noisy, at first, the sound is very annoying. However, after a period of around one hour, the person does not notice the sound anymore, and seems to have completely forgotten about it.
If a person lives in a home next to a busy road, over time, he gets used to the constant sound of traffic. In fact, if such a person moves to a quieter locale, the new silence might be distracting, and he might miss the familiar traffic noises.
Smell Sensory Adaptation: People who are regular smokers do not seem to notice the odor of cigarette smoke, because constant exposure to this stimulus makes them get used to it. This odor can be quite distracting to any non-smoker in the vicinity.
If a person wears a strong perfume, eventually, he will forget about the smell and will not notice it at all. However, any other person who comes close by will find the scent overpowering.
Touch Sensory Adaptation: If a person wears a watch or some jewelry, initially, he will feel the accessory against the skin. However, within a few minutes, the person will not notice this sensation, as the skin begins sensory adaptation. If the person purposefully changes the position of the watch, the sense of touch will become active again for a short while, before the repeat of sensory adaptation.
If a person is sitting on a chair with his arms on the armrests, the sense of touch on the arms activates instantly. However, over a period of time, the sensation gradually reduces, until it isn’t noticeable at all.
The phenomenon of neural adaptation is also seen in sessions of resistance training, where after a first few intense workouts, the muscles get used to the strain it has been subjected to, which leads to increase in strength, without any increase in the size.
Sight Sensory Adaptation: In our day-to-day lives, it is extremely rare for a person to look at a single unchanging place or object constantly, which means that, the chances of visual sensory adaptation occurring is very low. However, under a controlled environment, the sense of visual perception fades, and a person exposed to a constant visual stimulus shows reduction of response in the brain cells as compared to the initial stages, which leads to effects such as afterimages or motion aftereffects.
A good example of visual sensory adaptation can be seen, when a person who has been in a dark room comes out into a brightly-lit area. Initially, the brightness might feel discomforting, but with time, the eyes adapt with changes in the size of the pupil, and the bright light does not hurt the eyes anymore despite the brightness being of the same intensity.
Taste Sensory Adaptation: A meal is considered to be good or great only when the flavors are of different kinds. This kind of food excites the nerve cells, and get a strong response from the brain. However, if a person eats some food which is monotone in flavor, in a few minutes, the sense of taste loses its sensitivity, and the person may find it difficult to recognize the flavor even if it is strong, making the food unappetizing.
Sensory Adaptation vs. Habituation
Because they are so similar, sensory adaptation and habituation are often mistaken to be the same thing. However, here are a few fundamental differences:
- Neural adaptation is physiological, while habituation is attentional in nature.
- Sensory adaptation is not voluntary, while a person has at least a small degree of control over whether a stimulus is noticed or not, i.e., if a person has adapted to the taste of something, they cannot force themselves to taste the flavor.
- While the strength of a neural adaptation is directly related to the intensity of the stimulus, this is not true for habituation.
The functions of the brain regarding sensory adaption are still largely unexplored. However, new research is bringing hope to improve medical and rehab techniques, especially for people who may have suffered some sort of damage to the brain, which can lead to great advances in understanding human physiology as well.