for example, it has
been found that the beginner makes rapid progress up to the
point, say, where he can write fifty words a minute without
error; there is a long interval not infrequently before he can
raise his efficiency to the point of writing seventy words a
minute correctly. Analogous conditions have been observed
in the speed with which the sending and receiving of telegraphic
messages is learned. These "plateaux" of learning
are sometimes to be accounted for by muscular fatigue.
Frequently there is actual progress in learning during these
apparent intervals of marking time. Some of the less observable
features of skill in performance which only later become
overt in speed and accuracy are being attained during these
seemingly profitless and discouraging intervals. Not infrequently
in the acquisition of skill in the playing of tennis or
the piano, or in the solution of mathematical problems, a
decided gain in skill and speed comes after what seems to
be not only lack of progress but decided backsliding.[1] It is
this which led William James to quote with approval the
aphorism that one learns to skate in summer and swim in
winter.

DRILL _VERSUS_ ATTENTIVE REPETITION IN LEARNING. The rapidity
with which habits may be acquired and the permanency with
which they may be retained depend on other factors than
simply that of repetition. Mere mechanical drill is effective
in the acquisition of simple mechanical habits. The most
attentive appreciation of the proper things to be done in playing
tennis or the piano will not by itself make one an expert in
those activities. The effective responses must actually be
performed in order that the appropriate connections within
the nervous system may be made, and may become habitual.
A habit is physiologically nothing but a certain set or direction
given to paths in the nervous system. These paths become
fixed, embedded, and ingrained only when nerve currents
pass over them time and time again.

[Footnote 1: See Ladd and Woodworth: _Physiological Psychology_, pp. 542-92.]

Mere repetition, on the other hand, will not suffice in the
acquisition of complex habits of action. The learning of
these requires a deliberate noting and appreciation of the
significant factors in the performance of an activity, and the
consciously chosen repetition of these in succeeding instances
until the habit is well fixed. One reason why animals cannot
be taught so wide a variety of complex habi