It's different for every kid. Basically what it is..they don't process sensory input like a typical kid does. Lights are too bright, sounds are too loud, tastes are too strong, touch is bothersome, smells all stink...or the opposite. It doesn't always involve all of the senses, either.
Also in there is proprioceptive as well...knowing where the body is in space.
Some kids need more sensory input, some have to have less. Some kids have to have a specific type of clothing (only sweats with no elastic, or only white tagless shirts, etc) for some it has to be a certain material, for others it doesn't matter.
It's not diagnosed by a doctor, but by an OT. And it's not an official "medical" diagnosis. There is no "curing" it, only teaching them to cope with it.
I recommend "Out of Sync Child".
at 8:55 AM on Aug. 21, 2009