here very simple.

But sometimes the stimulus is more complex, not merely the simple
excitation of one sense organ, but a complicated stimulation of an
organ, or the simultaneous stimulation of several organs. In playing
ball, the stimulus for the batter is the on-coming ball. The response is
the stroke. This case is much more complex than the reflex closing of
the eyelids. The ball may be pitched in many different ways and the
response changes with these variations.

In piano playing, the stimulus is the notes written in their particular
places on the staff. Not only must the position of the notes on the
staff be taken into account, but also many other things, such as sharps
and flats, and various characters which give directions as to the manner
in which the music is to be played. The striking of the notes in the
proper order, in the proper time, and with the proper force, is the
response.

In typewriting, the stimulus is the copy, or the idea of what is to be
written, and the response is the striking of the keys in the proper
order. Speaking generally, we may say that the stimulus is the force or
forces which excite the sense organs, and thereby, through the nervous
system, bring about a muscular response.

This is the ordinary type of action, but we have already indicated a
different type. In speaking of typewriting we said the stimulus might be
either the copy or ideas. One can write from copy or dictation, in which
the stimulus is the written or spoken word, but one can also write as
one thinks of what one wishes to write. The latter is known as
_centrally initiated action_. That is to say, the stimulus comes from