"I take over a thousand pictures of a person's face when I look at them. That's why we have a hard time looking at people" ~ Carly Fleischmann
I actually like that self report because it indicates some very important hypothesis about how the brain is self connected in an autistic person different from a "normal" person.
Namely, I'd propose that the reason there is sensory over load is because the normal mechanism for encapsulating and possibly shifting attention to different cognitive aspects under consideration is short circuited in some way...such that there is a bias toward external stimuli.
Our cognitive dynamics involves a balance, an equilibrium between the external sensation and the internal sensation dimension, I assert (in many of my blog posts from the last few years) that consciousness is nothing more than the time variant dance of this interplay between what the world is presenting to us across those "extrasensory" inputs and what our "insensory" inputs are demanding.
Extrasensory inputs are your standard senses, Visual, Auditory, Gustatory, Somtatsensory, Olfactory...your Insensory inputs are the autonomic drivers that demand your attention....boil down basically to food and sex.
I hypothesize that everything you do, everything you think is in some way guided by the continuous attempt to balance the extrasensory against the insensory drives.
That said, there needs to be a filtering mechanism in place to ensure that there is no over stimulation (in both directions) which delays convergence to "action" once sensation and processing have concluded...in fact, switching attention is a precisely necessary function to keep the dynamic cognitive drive moving forward.
Last year research for the first time identified how attention is performed as a key aspect of the function of Astrocytes (glial cells)...the "other" major cell type (in fact the most numerous) in the brain beside neurons. Up until this study their full role was not known...now it appears their purpose is to serve as attentional switches...they store a short term representation of a currently sensed signal in a given dimension of experience and resonate that back at a given rate to enable it to persist LONG ENOUGH to be processed...but this begs the question of what happens if they persist the signal TOO LONG?
It would seem they'd be re-echoing cues for continued attention when there is no need (beyond the processing time frame) this could very well be the source of the sensory over load that Carly reports in her experience and that seems to be a hallmark of all the autistic. In electronic and computer design the master beat of the dynamism of computational functions are set by a device called a clock which is stepped in various ways so that different systems can be invoked in a precise way as needed to provide synchrony critical to the function of the overall system, it is reasonable to wonder if the brain requires a similar set of stepped timing signals that are applied to different aspects of cognitive processing so as to effect a smooth and convergent dynamism as the possessing agent interacts with the world, doing so efficiently would be key to be able to focus on events in the world for just the right period of time necessary to optimize the achieving of all goals.
Also, it could be at work in a differential way across the brain...with some sensations being more sensitive to attention than others (say vision over sound, or smell over touch)...there is no reason to presume the pathology is homogeneous across astrocyte tissue though that is also possible.