A couple links on autism and driving
Interactive Autism Network: Driving with ASD
Getting behind the wheel of a car is a rite of passage for many teenagers, but for high-functioning individuals with autism spectrum disorders (ASDs) this task may prove particularly difficult. Along with the impulsivity, inexperience, and other traits of adolescence and young adulthood that can make driving a challenge, an individual with ASD may find him- or herself struggling with potential obstacles posed by autism itself. Can he or she quickly intuit and react to the "big picture" of any given driving situation? Can he or she interpret and respond to the actions, attitudes, or intentions of other drivers? Can he or she keep calm, neither overly anxious nor angry? Can he or she avoid "zoning out"?
And a paper referenced in that, no longer at its original URL, but still on the Wayback Machine:
Visual perceptual abilities in children and adults with autism spectrum disorders
The weak coherence account theory claims that persons with ASD have problems processing information on a global level and thus favours information on a local level. This means that those with ASD have difficulties in gaining central meaning from information, as they tend to focus on details without relevance to the global meaning of the information [46, 47]. [...] The tendency among persons with ASD to focus on details (local processing) presumably leads to difficulties in settings also for others if they take for granted a focus directed towards the central (global) meaning in visually presented information.
More musings on this after the break...
This is a big part of my issues with driving. And I think it was worsened by the fact that even professional instructors just did not get my perceptual quirks. After all, like the above-quoted paper points out... if you've never experienced non-global visual processing, how would you know anyone had anything different?
And that's exactly the problem. None of the instruction that I've gotten teaches how to compensate for this, because nobody has even anticipated it. So my brain is taking in way too many details for me to even handle, and I don't know which ones are safe to eliminate, and so I get totally overloaded, and my brain starts to drop the information that actually is important while not noticing that, say, I'm getting closer and closer to the car in front of me.
Oh, that's another thing. Things like speed and positioning in lane, that everyone just takes for granted as automatic? That's never become automatic for me. Even after years of practice, I have to consciously focus on those things if I want to maintain a constant speed in a hilly area (where speed is not directly proportional to pressure on the accelerator), or if I don't want to veer out of my lane. Also not helped by the fact that I still have a tendency to center myself in the lane rather than the car as a whole-- there's that local vs. global processing again!
One really weird local-processing thing I had, incidentally, was something I worked with an occupational therapist on. For some reason, my brain didn't immediately connect that what was happening in the windshield, the side windows, and the rear-view mirrors were all part of the same scene-- it's like my brain treated them as disconnected windows rather than viewports on the same scene. I've gotten better at that after taking the therapist's advice of putting some paper strips on my TV to split it into three 'windows'.
Another local-vs.-global thing that we discovered, that I've also worked on but that I still have to focus on consciously, is that my brain tends to cluster visual input differently than neurotypicals. So, like, say you've got cones at even distances on the side of the road, alternating on the left and right sides... most people will see it as left, right, left, right, left, right. I see a bunch of cones on the left, then a bunch of cones on the right. In other words, my brain clusters stuff horizontally, while most people's brains seem to do it by forward distance. This definitely explains my issues perceiving patterns amongst lanes of traffic.