It's easy to do two things at the same time, as long as one of those actions is a practiced skill that you can do almost automatically. For example, walking and talking is easy. And some people can play the guitar and sing, as long as they have practiced both of those skills until one requires virtually no conscious thought. But you can't do two things at the same time that both require original thinking. I know this first hand because my wife, Shelly, likes to bring up conversations in the car that involve rotating three-dimensional objects in my mind while expecting me to simultaneously navigating to our destination. This doesn't work out so well. The actual driving of the car is easy, because that is a practiced skill. But trying to imagine the correct route to our destination is impossible for me if Shelly is simultaneously asking me to imagine the optimal placement of patio furniture.
The other day, as I was cleaning pasta sauce off of every inch of the inside of the microwave, I was reminding Shelly of my bandwidth limitation for spatial manipulation. I blamed her for engaging me in a conversation involving the manipulation of objects while expecting that I would simultaneously be able to imagine the proper combination of pasta, sauce, a bowl, and (this next part is key) a cover inside a microwave. I managed to put four out of five objects in the right place, and frankly felt good about it.
I have a theory that music appreciation resides in the same part of your brain where you think about yourself. That might be why it's good to listen to music while doing boring tasks, such as going for a long run, because music interferes with your mind's ability to think about yourself. I also find it impossible to do any sort of creative writing while listening to music, perhaps for the same reason: Creativity springs from a deep examination of self, which you then generalize, and music seems to share that bandwidth. I can, however, listen to music and manipulate three-dimensional objects in my mind just fine. Those functions don't seem to interfere with each other.
I wonder if we humans will get to a point where we understand how to manage the different parts of our brains in the best fashion. For example, if you have an important upcoming task that involves manipulating objects in your mind, is it better to practice spatial tasks all morning, or better to rest that capacity of your brain until you need it?
During one period of my life I wrote a number of computer programs that involved intense manipulation of objects in my mind, for hours each day. I discovered that it was difficult to be social at night when my mind had been manipulating object during the day. It felt as if I were deep inside a cave and yelling to the people who stood at the cave opening. It seemed as if the practice of programming interfered with, or exhausted, the part of my brain that handles social skills.
It is generally agreed that playing soccer is a good crossover skill for playing tennis, because of the footwork. Could we get to the point of understanding the brain where, for example, we tutor someone who is struggling in math by asking him to do non-math tasks that are complementary to the math-handling part of the brain? I wonder, does playing a highly spatial video game for hours a day help your math skills, exhaust them, or have no impact?
If you have a date in the evening, will you be at your most witty and charming if you spent the hours ahead of the date doing light exercise, reading a novel, or assembling some IKEA furniture? I'll bet there's a right answer to that question.