Selective Sound Sensitivity Syndrome, these days usually shortened to “Misophonia,” refers to a neurobehavioral syndrome that causes those afflicted to experience heightened autonomic nervous system arousal when they’re exposed to certain sounds.
In practice, that means specific noises will trigger negatively valenced emotional states like anger and anxiety and general irritability, and those emotional states will tend to be amplified for no obvious reason: someone becoming irrationally angry at their partner’s chewing sounds, for instance, or made viscerally uncomfortable by the sound of their cubicle-mate’s keyboard typing.
In some cases exposure to these sounds will evoke something like a fight-or-flight response, and research suggests this neurological arousal has less to do with the volume of the sound in question, and more to do with its pattern, that pattern somehow having been categorized as a trigger to the person experiencing the misophonic episode.
The term “Conditioned Aversive Response Disorder” has been proposed as a potentially more descriptive and accurate monicker for this condition, as there’s some evidence that it’s a conditioned (or learned-over-time) response, potentially from something encountered in childhood.
Other theories, though, posit that it might be more akin to some types of anxiety disorder, possibly paired with a type of synesthesia that causes certain sounds to be interpreted as alarming and dangerous, rather than mere indications that someone nearby is chewing or typing.
There’s also reason to believe that misophonia might be related to obsessive-compulsive disorders, as the distress sufferers experience (and as much as 10% of the human population may experience some degree of misophonia, according to one study) seems to follow similar pathways and seems to be triggered by similar mechanisms as those seen in people with various types of OCD.
This is still a relative frontier topic in the world of neurology, so there’s a lot of speculation and debate about categorization, but not a lot of concrete answers, diagnostic tools, or means of managing its symptoms at this point.
There have been attempts to help people suffering from extreme cases of misophonia using techniques borrowed from the treatment of tinnitus, OCD, and anxiety and depression (with mixed results), which again points at the possibility that this is a subset condition, but we can’t say that for certain yet.
The existence of misophonia, though, gestures at the possibility that our responses to external variables may not always be as clear-cut and neutral as we assume, and just as our mood might influence the valence of our response to hearing bad news or getting into a fender-bender, so too might our brains’ categorization of certain sounds (or other qualia) dramatically change our experience of, and neurological reaction to, these bits of sensory data.