the
brain, in the process of making a skilled movement dealing with a
perceived object. First, sensation; second, perception of the object;
third, cooerdinating preparation for the act; and fourth, execution of
the act by the motor area arousing the lower motor centers and through
them the muscles. The first response is like receiving signals {429}
or code messages; the second deciphers the messages and knows the
state of affairs; the third plans action; and the fourth sends out
orders to the agents that perform the action.

The distinction between perception and preparation for action is
sometimes rather difficult to draw. The twelve o'clock whistle means
time to drop your tools, and it is hard to draw a line between knowing
the fact and beginning the act. On the other hand, when my watch tells
me the noon hour is almost over, some little time may be required
before I get into motion. Where there is no block or inhibition, the
chain of responses runs off with such speed as to seem a single
response. But a block may occur at any one of several places. It may
check the actual movement, as in the "delayed reaction", [Footnote:
See p. 76.] and in cases where we itch to do something yet check
ourselves. Here the preparation occurs, but the execution is checked.
Sometimes the block occurs between perception and preparation, when we
know a fact but find nothing to do about it or hesitate between two
ways of acting. Sometimes, also, the block occurs between sensation
and perception; a sudden loud noise will sometimes throw a person into
a momentary state of confusion during which he is unable to recognize
the noise.

Blocking of response at different stages can be illustrated very well
in the case of anger. The irritating stimulus gives a prompt fighting
reaction, unless checked at some stage. When the check prevents me
from actually striking the offending person, but leaves me clenching
my fist and gnashing my teeth, the chain of responses has evidently
gone as far as readiness for action, and been blocked between that
stage and the stage of execution. Probably the inhibitory influence
here is anticipation of bad consequences. The block may occur one
stage further back, when I say to myself that {430} I mustn't let
myself get "all riled up" since it will spoil my morning's work; here,
instead of substituting the clenched fist for actual fighting, I
substitute a bored or contemptuous attitude for the pugnacious
attitude. A