There are times when the ability to use two of the senses with
reasonable accuracy at the same time will be of value. It is not
possible for either of the senses to produce perfect attention while
working in conjunction with one another. We can attend to only one
thing at a time and do it well, but "Divided Attention" is possible.
Under the chapter on Attention and Concentration, on page 75, you will
find an explanation of "Divided Attention," which should be read before
going farther with these exercises.