I feel in a similar way about this issue. Despite the concept of multi-tasking, one cannot properly concentrate on more than one task simultaneously, which is why answering one's mobile phone whilst driving a car is not recommended.
Classical music is often so magnificent, complex, elaborate and emotionally overpowering, that to even attempt to relegate it to the status of non-intrusive background music would be a crying shame.
There you are: no constants, no absolutes. My wife could always manage a hundred different things at the same time whereas I never could; she hated music in the car if she was driving but I love it. As a child, I used to do my homework with the radio switched on and it did me no harm whatsoever. The single time in the car when I had to switch music off was when reversing into a parking space. That requires so much absolute concentration that even conversation has to cease. I say had to switch off because I now drive in silent mode. Why? Because the bloody trafficators donít make enough noise and because in the Fiesta the blinking warning lights are placed at the extreme edges of the instrument panel where the hands obscure them in the driving position. And why should any of that create a problem? Because the damned indicators donít cancel soon enough: they continue to flash unless you almost do a loop in the opposite direction! When your car is constantly indicating either left or right, it will ultimately cause an accident when you do make that turn. I went back to the dealer and before Iíd finished my tale he laughed and said theyíre all the same: even his own Focus does itÖ design, bloody design!
However, I donít really believe that that implies a lack of concentration on my driving when Iím driving forwards. In fact, I believe that nobody drives with their mind switched onto Ďdrivingí per se; I believe that after a while one drives on auto, subconsciously, all the time. Iíve lost count of the number of times I realise that I have no idea whether I got to where I was going easily or whether I had to stop at lights etc. and stopping at lights here is memorable: we have very few. I know exactly why I have to switch off when reversing, though: cars since the 70s have generally suffered from dreadful design faults that limit parking ability: you can no longer see where the frigginí corners are. In many, you canít even see where anything might be since vision ends at the edge of the dashboard. Progress, yes. Why do you imagine they invented those expensive parking bleepers if not to screw even more money out of us whilst hiding the basic design flaw that creates the need in the first place?
Now, regarding working at the computer, whether typing messages as now, or working on a picture, I have no idea what the last song I heard might have been: itís simply a very pleasant atmosphere in which to do that which I am doing; itís a cocoon of comfort. Just as it is when taking the pictures.