Hey Christine,
Yes, I think "sensory overload" could be a good way of putting it. These barriers (assuming they're real) could exist for a good reason - to prevent such an overload. I just now remembered where the idea came from originally. It was in an episode of "The Others" (on Fox8) the other week. I wondered if there was any truth to it after watching that show. The topic about mental disablities must have jogged my own memory.
As said in the television series, perhaps these barriers are more like filters, that work to gently sift through information and determine what we are ready to cope with and what we are not but, in some people, something goes completely skewiff and those barriers break down.
Hypnotherapy was and still is used in many cases. In some it works, in others it doesn't. I think that it would take more than just hypnotherapy to re-build these barriers or filters, although I think it would certainly play a role. I think that some of the drugs that are currently used only work to slow a person, or rather their reactions down, so that they behave in a calm acceptable way. It doesn't necessarily mean that they are no longer seeing things, just that the drugs prevent them from reacting.
Perhaps one day, if we develop it further, things like telepathy might play a more successful role. We would be able to go into someone's mind, in a literal sense, and help them to rebuild whichever barriers are broken?
It's all just conjecture really but I find the idea that there could be some significant help for people with these kinds of problems a good one. The real trick has always been to identify the cause.
Flutterbit