Recent articles concerning multi-tasking address the possibility that people can do two things at the same time (more complex than walking and chewing gum), if the two actions involve opposite sides of the brain.

Other researchers posit that multi-tasking is possible if the tasks involve different areas of the brain (e.g., visual vs. auditory).

For myself, I know that I do a lot of the following: I set "pay attention" threshholds for critical events, thus freeing me to attend to second or third items.

Driving is a perfect example. My color recognition is always set for red, especially red suddenly appearing. Whatever else I'm doing in the car (watching pedestrians, listening to music, checking cross traffic), a sudden appearance of red will trigger the attention threshhold.

At night, it's the occlusion of oncoming headlights that will grab my eye. Could be a pedestrian in the dark crossing the street, could be another vehicle, could be anything, but occlusion of headlights is a definite threshhold.

I play music in my office. Mostly it's background, but a favorite track will bring it to the fore. The telephone will supersede music. Person's voice will trump all (which is why I find co-worker's loud chatter about pending camping trip and her partner's knee and her dog's antics so annoying).

So I'm wondering if multi-tasking is more complex than two equal priority tasks (researchers having subjects count red circles, then blue crosses), but a question of having tasks one more important than the other (thus taking precedence when both require attention) and having threshhold triggers set for "emergency" response.

John's comment just made me remember: I listen better when I'm knitting or crocheting. I used to take notes in college (and doodle) because it helped me concentrate--I never re-read my own notes. I think the multi-tasking issue is a lot more complex than researchers are now addressing.