On the AutAdvo list, one of the NT members asked about sensory overload. This is certainly a topic of importance, given how strongly it affects the life of the autistic person, so I posted a rather detailed reply. I was surprised by the feedback I received for that post... it was overwhelmingly positive, and several people asked that I post it on my site so that others can read it. I was happy to do that, certainly, as helping NTs to understand autistics is one of the purposes of this site.
I will include the original citations from the post to which I replied, since the responses I typed were geared toward the questions as posted. Those original questions will have the greater than '>' symbol in front of them.
It is different with each of us, but the short answer is 'all.' It can be any of the senses... I know that loud noises, or even persistent quiet ones, add significantly to the sensory load, and certain types of noises are worse than others. In time, my nervous system will return to normal if no other loads are placed on it, but if there are more noises or other loads present, the stress level will build faster than I can burn it off, and I will get overloaded.
What type of sensory overload? Is it auditory, visual, other, all?
I have described it like this. It is as if there is a reservoir of sorts that each of us has. This reservoir starts off empty, but the things we experience throughout the day fill it up. Any sensory load (which I define as stimulus that the nervous system is describing to the brain-- in other words, anything that can be felt) or other nervous system load will cause the reservoir to take on more fluid. It does not have to be unpleasant-- even pleasant kinds of sensory load (like enjoying a movie at a theater-- I like it, but it does present a notable sensory load) fill up the reservoir. Things like the smell of people's perfume, bright lights, constant motion (I cannot tolerate seeing too much motion, especially if there is more than one velocity of motion), noise (the more painful or annoying, the worse), etc., all tend to fill up the reservoir.
Other things also cause the level in the reservoir to rise. Social contact does this. It is not just the noise of people talking and seeing them move that causes the sensory load. For one thing, I have auditory processing problems, so I really have to work to understand spoken words. That causes the reservoir level to rise. Being ready to interact, or what I call being in interactive mode, is also difficult, and causes the level to rise.
Finally, thinking about what the other person said and devising a response real-time (as opposed to email, where I can respond at my leisure) also causes the reservoir level to rise rather quickly. The more difficult the interaction, the more quickly the level rises. In other words, if I am talking to other autistics, it rises slower, because I can talk more freely than I can with NTs, where I always have to try to guess what needs to be said. That is exhausting, and that exhaustion shows as rapidly rising levels in that reservoir.
I am stressed most of the time. Just for the fun of it, I took an online stress test (using the classical definition of stress as a bad thing, which is not exactly true, as I will get to in a moment) this morning, and it said that I had a stress level of 7%... "Your stress level barely registers." Oh, if only that were true. I don't have any way to measure this, but I think I am probably more stressed than most people that do all of the stressful things that would give them a high score on that test.
Things that are low-stress or that reduce stress in NTs are horrible for me. Stress, of course, adds to sensory load. Fear, anger, and any other powerful emotion makes the level in the reservoir rise rapidly. Happy contentedness makes the level go down, but positive anticipation, suspense, or excitement, at least for me, cause the level to rise, not fall. Having things not go according to expectation, or having the routine broken, causes the level to go up. Indulging my perseverations (like researching a topic with which I am obsessed) reduces the level in the reservoir, even if it involves things that are usually stressful, like interacting with people.
Just about everything I do outside the home makes the fluid level go up. As you can see, living in this world is in itself a highly stressful, sensory-loading kind of thing for my kind. Things that you do not notice can cause huge problems for us.
When I get time alone in a dark, quiet place, I can burn off some of the sensory load and cause the reservoir to become less full. Rocking, flapping, and stimming also help me to lower the level in the reservoir. Our tendencies to isolate ourselves, to flap or rock, to routinize our lives, to put things in a specific order, et cetera, are, in part, ways of reducing the level in the reservoir, or keeping it from filling up in the first place. In my case, I do many of these things as the reservoir begins to fill... so it fills much more slowly. My stims are vital to me being able to cope with the world, and I do them wherever I am if I need to. Others have been taught not to do these in public, so they let the reservoir fill up until they get to a place where they can recover from the strain and decompress.
This is less efficient than doing so as the reservoir first begins to fill, because the higher the level in the reservoir, the more quickly the reservoir fills in response to the next sensory load event. It's not a linear thing. When I am calm (reservoir empty), I can handle a lot more without adding to the reservoir level than I can when that reservoir is half full.
Keep in mind that I use "stress" more broadly than a lot of people. Stress can have many forms, and not all of them are bad. Hearing a funny joke that makes me laugh is a kind of stress. Riding a roller coaster, which I enjoy, is pretty stressful (it adds sensory load, which fills the reservoir). The difference is that many of the eustresses (good stress) also cause a release of endorphins, which helps to keep the stress in check.
When the reservoir fills, obviously, the ability to tolerate further sensory or nervous system load is nil. Any more sensory load will cause the reservoir to overflow or burst (it's just an analogy, so you pick the image that works for you). Overload is a failure to manage nervous system load levels (a slightly more accurate way to put it than sensory load, since some of the load is from within, as with emotion).
Sensory overload can lead to what type of meltdown?Any type. Actually, the term I would use would be overload-- a meltdown, I think, is usually a severe tantrum with a total collapse of coping ability and frontal lobe function, which is one of several possible responses to overload. In my case, I tend to shut down, not have a tantrum. I can feel my ability to think disappear. My voice becomes more monotonic than normal, and I start talking in gibberish. People ask me things when I am in that state, and all I can say is "I
don't know." I really don't know when I am like that... I barely know my name. In that state, my brain is ignoring most of the senses, so I have a pronounced tunnel-vision effect, and I am all but unaware of sounds around me. I can't smell anything in that state.
With the frontal lobe shut down, there is not much nervous system load, so I do not usually get worse than that. I have, though, especially when I was younger. Many times in school, the teacher would notice that I was not moving, just staring straight ahead with glazed eyes. She would talk to me, and I would not even notice. She got closer and addressed me from right next to me, and I would not notice. I was offline, for the most part.
Some of my kind have a tantrum, yell, hit, or do other things when they overload. I don't tend to do that. I just zombify.
It is distinctly unpleasant to be overloaded, and it takes a lot longer to recover from an overload than it would to recover from having the reservoir 90% full. Once the reservoir gets more than, say, 75% full, you'll see some signs that overload is coming. I can feel it when I have reached that point, or when the sensory load is so great that the reservoir is filling very rapidly. To others around me, it can be seen as sharp, fast rocking and a lot of wiping of my palms down my face.