My mom picks Jake up after school since I'm still at work when he gets out. She has to drive through a "pick-up" line with a sign on her dash given to us by the school, which has Jake's full name on it. A teacher then walks through the car line with a two-way radio, calling of the names of kids coming up in the next group of 20 or so cars.
Several times during this process the last year or two, Jake's name has been called and he hasn't come out to the car. They eventually find him, sitting at a table where he's supposed to be, but unaware that his name was called. The first time everyone panicked. For about 30 seconds they thought he was lost.
This happened again last week, and when I asked Jake what happened, Jake said "Sometimes the other kids just get too loud, and I have to shut my ears off."
I was fascinated by what he said, because he's never been able to put the experience into words. He has a hard time recognizing how he feels or expressing anything but concrete concepts.
Essentially what happens is that Jake gets sensory over-loaded (too many signals being brought in by his senses all at once) and as a coping mechanism, he blocks one or more out. Now there's Auditory Processing Disorder, where there's nothing wrong with a child's hearing per se, but what they hear doesn't make it to their brain (or gets there, and can't be interpreted correctly) - and I sometimes have thought Jake has a smattering of APD - but in this case I think that for whatever reason, he just can't deal with an excess of commotion. However his brain is processing and organizing sensory information, it just can't keep up - so it shuts that sense off instead.
The good news is that Jake has gotten progressively better at dealing with loud noises and functioning when he's uncomfortable - for me, what I look for is progress (rather than hoping he'll magically stop having these issues.) And the people in the pick-up line have learned that this happens sometimes, and they don't have to shut things down for a possible missing child until they've called his name again. ;)