ns. It is the same in {324} learning to
typewrite. First you must learn your alphabet of letter-striking
movements; by degrees you reduce these finger movements to firm
habits, and are then in the letter-habit stage, in which you spell out
each word as you write it. After a time, you write a familiar word
without spelling it, by a cooerdinated series of finger movements; you
write by word units, and later, in part, by phrase units; and these
higher units give you speed and accuracy.

Along with this increase in the size of the reaction-units employed
goes another factor of skill that is really very remarkable. This is
the "overlapping" of different reactions, a species of doing two or
more things at once, only that the two or more reactions are really
parts of the same total activity. The simplest sort of overlap can be
illustrated at an early stage in learning to typewrite. The absolute
beginner at the typewriter, in writing "and", pauses after each letter
to get his bearings before starting on the next; but after a small
amount of practice he will locate the second letter on the keyboard
while his finger is still in the act of striking the first letter.
Thus the sensory part of the reaction to the second letter commences
before the motor part of reacting to the first letter is finished; and
this overlap does away with pauses between letters and makes the
writing smoother and more rapid.

With further practice in typewriting, when word habits and phrase
habits are acquired, overlap goes to much greater lengths. One expert
kept her eyes on the copy about four words ahead of her fingers on the
keyboard, and thus was reacting to about four words at the same time:
one word was just being read from the copy, one word was being
written, and the two words between were being organized and prepared
for actual writing. The human typewriting mechanism, consisting of
eye, optic nerve, parts of the brain and cord, motor nerves and
muscles, works somewhat like one of {325} those elaborate machines
which receive raw material steadily at one end perform a series of
operations upon it, and keep turning out finished product at the other
end.

All this is very remarkable, but the same sort of overlapping and
working with large units can be duplicated in many linguistic
performances that every one makes. In reading aloud, the eyes keep
well ahead of the voice, and seeing, understanding and pronouncing are
all applied simultaneously to