For example, we feel putting on clothes, but then very quickly, aren’t aware of that sensation anymore. Similarly, when you encounter a smell, the sensation begins to diminish. While I am glad that I become less aware of a foul smell, why does this happen? Would it not be safer to remain aware of bad smells so that you remain deterred from bad food or potential disease exposure? At the same time, does this happen with other senses like hearing? I remain constantly aware of the noise of my fan if I leave it on, so if that sense doesn’t diminish, why is that?
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Our brains use selective attention/filtering. When we take in stimuli, it’s sent to the thalamus (except for smell) by the cranial nerves, then the cerebral cortex, where it’s either classified as useful, or it’s filtered out. The sensation of our clothes is very normal and generally unimportant, so the cerebral cortex doesn’t send it off for further analysis. This is actually nicknamed the “cocktail party effect” in terms of hearing—how we can be at a party, surrounded by conversations and noise, but we still manage to focus solely on our discussion. The fan is there, but it’s not important.
Scent, on the other hand, goes through the limbic system to the thalamus. But it does something similar, and filters scents out. It’s commonly called being “nose blind.” We get used to the bad smell by our brain basically saying, “okay, this isn’t dangerous,” and drowning it out like it does other distractions, so it can go back to its job sensing abnormal smells.
Of course, there are plenty of disorders that can occur as to sensory perception, too. Schizophrenia, for example, can make it hard to ignore the fabric against your skin, synesthesia can make your brain interpret colors as tastes, ADHD can involve hyperfixation, etc.
There is a term call **synaptic fatigue.**
In short our senses depend on the neuron receptors, their connections to our brain and the neurotransmitters they use to communicate with each other. The receptor might deplete all their neurotransmitter to a stimulation that is constant and of the same intensity. So that way the signal that reaches the brain is lower and you feel less that stimulation.
Because after a while it’s less help to be reminded that a certain stimuli is still there than it is to be notified that new stimuli has shown up.
For example if you lived in a field full of flowers, and you never got desensitized to the smell of those flowers, then you’d never notice the predator who does NOT smell like flowers coming up behind you.
EDIT: Or maybe since our sense of smell isn’t that spectacular, maybe there’s some food that you always get in the wild, so you eventually become less sensitive to the taste of that food on its own because you need to be able to detect if you’ve picked a rotten or poisoned fruit.
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