Simultaneous control and visual attention. (Don’t try this at work!)
It is difficult to do one non-trivial task that requires attention with one hand and other task with the other hand; especially without practicing. Try, for example, balancing a pen on the forefinger of your right hand, while typing with your left hand. Playing piano both-hands is that kind of task that needs practicing. (What actually happens in piano playing is that as the artists develop their expertise, they will not anymore waste the precious visual attention on their hands.)
A step to make this even more challenging is to control two things simultaneously using one hand only. Try this game. (Don’t blame me if it took your working day away.)
Here are my scores in the orders of trials (technical-errors excluded): 3.532, 6.177, 7.265, 15.143, 9.731, 9.84, 8.4, 4.9, 17.086, 7.76, 11.434, 9.851, 21.841, 12.907.
It seems there are some peaks in the performance with increasing number of trials. After each of the peaks the performance for a while stabilizes on a level that is higher that the level before the peak. In other words, some learning seems to take place. What I’d like to see, however, is how visual attention patterns develop with the trials. Anybody is interested to come for a short time being eye-tracked?