An unpleasant state of overstimulation in which too much information comes in through the senses at once for the brain to process. This may cause pain, nausea, shutdown, meltdown, or inability to comprehend further information.
This state is common in autistic people, people with migraines, hangovers, certain forms of brain damage, sensory integration disorder, and others for whom sensory processing is difficult or unusual. The book The Highly Sensitive Person was written with easily-overloaded people in mind, although it covers aspects of sensitivity besides sensory sensitivities. One brain injury specialist calls sensory overload "The Meijers Effect" based on a particularly overloading store.1
However, there are very few people who cannot experience sensory overload under the right circumstances. Most parents would probably attest that it is overloading to deal with one crying baby and two fighting children while trying to fix dinner and talk on the telephone at the same time. Dr. Glen Johnson makes the distinction, though, that while many people might find an environment barely tolerable, a person subject to sensory overload might say "I have to get out now! I can't take this anymore!" and experience more serious cognitive and health repercussions than the average person.1 It's a matter of degree.
Some sensory overload comes from a stimulus that is immediately too intense for the person experiencing it. For instance, a jackhammer, a bright strobe light, clothing of an intolerable texture, the sound of people's voices, humming refrigerators, or fluorescent lighting. What overloads one person might not faze another. Some sensory overload is more gradual and cumulative, with a minor irritant building up over time to the point of overload. Some sensory overload comes from having to deal with too many stimuli at the same time.
You can recognize when you are starting to become overloaded by changes in the way you respond to information. You might feel a physical sensation, such as pain or nausea. You might become more irritable or anxious than usual. Things that are normally easy to do can become more difficult to do. You might start looking around and finding that you can understand less of your surroundings than usual, and have to strain harder to make sense of things. Or you might not notice you're overloaded until someone tries to get you to pay attention to just one more thing and you lose your temper and scream at them.
When overloaded, it is useful to escape the offending stimulus and spend some time resting. Some people find it useful to substitute a non-overloading stimulus for the overloading stimulus. For example, if somone is becoming overloaded by the light touch of his clothing, he might prefer pressing himself against a wall to feel deep pressure. Otherwise, being in a quiet, dark, comfortable location can work.
If you are prone to overload, taking rest breaks regularly throughout the day might help prevent it. Many autistic people find that regular stimming, such as rocking, reduces the risk of overload and reduces any overload already present. You can also use a single intense stimulus to block out unpleasant stimuli, or focus entirely on one aspect of your environment and block out the rest. Dark glasses, earplugs, headphones, weighted vests and blankets, and hats with brims can also be useful.
Notably, much of the seemingly purposeless2 behavior of autistic people is either a reaction to sensory overload or an attempt to prevent sensory overload. We are often trained out of this behavior without being given any useful substitute, with the results being increased overload and decreased ability to sustain our abilities over the long term.
Example Usage: "I had to go pick up my friend at a busy airport today. Talk about sensory overload!"
1 Johnson, Glen. "Getting Overloaded," The Traumatic Brain Injury Survival Guide. http://www.tbiguide.com/getoverloaded.html. Accessed March 15, 2005.
2 This behavior is obviously not purposeless, but literature on autism often describes us as throwing tantrums for no reason, engaging in non-functional rituals, doing pointless things, and moving in purposeless ways. The resulting attitudes among professionals have often harmed autistic people.