When I'm driving with a passenger and conversing with them, I seem to only be able to actually focus on one of those tasks at a time.

If I am concentrating on the road, I've noticed that I tend to block out the passenger. Sometimes what the passenger says will get processed a good 5 seconds or so later when I'm in safer circumstances (straight driving in my lane). And if I'm instead thinking about what the occupant is saying, I will tend to miss turns that I know full well I need to take.

During any of this, however, I am driving fairly well. I have never had an accident in my 14 years on the road. But my brain is apparently focusing its full cognitive abilities on the road and traffic, but leaves little else to work with in that regard.

You can either tell me how your day went, or we can get to the restaurant. But they are somewhat mutually exclusive.