nkage with T is so strengthened by exercise that
T, or we may say S, comes to give the correct response without
hesitation.]

{410}

2. Learning to balance on a bicycle.

When the beginner feels the bicycle tipping to the left, he naturally
responds by leaning to the right, and even by turning the wheel to the
right. Result unsatisfactory--strained position and further tipping to
the left. As the bicyclist is about to fall, he saves himself by a
response which he has previously learned in balancing on his feet; he
extends his foot to the left, which amounts to a response to the
ground on the left as a good base of support. Now let him sometime
respond to the ground on his left by turning his wheel that way, and,
to his surprise and gratification, he finds the tipping overcome, and
his balance well maintained. The response of turning to the left,
originally made to the ground on the left (but in part to the
tipping), becomes so linked with the tipping as to be the prompt
reaction whenever tipping is felt. The diagram of this process would
be the same as for the preceding instance.

D. Substitute Response, the Response Being a Higher Motor Unit

1. The brake and clutch combination in driving an automobile.

This may serve as an instance of _simultaneous cooerdination_, since
the two movements which are combined into a higher unit are executed
simultaneously. The beginner in driving an automobile often has
considerable trouble in learning to release the "clutch", which,
operated by the left foot, ungears the car from the engine, and so
permits the car to be stopped without stopping the engine. The foot
brake, operated by the right foot, is comparatively easy to master,
because the necessity for stopping the car is a perfectly clear and
definite stimulus. Now, when the beginner gets a brake-stimulus, he
responds promptly with his right foot, but neglects to employ his left
foot on the clutch, because he has no effective clutch-stimulus; there
is nothing {411} in the situation that reminds him of the clutch.
Result, engine stalled, ridicule for the driver. Next time, perhaps,
he _thinks_ "clutch" when he gets the brake-stimulus, and this
thought, being itself a clutch-stimulus, arouses the clutch-response
simultaneously with the brake-response. After doing this a number of
times, the driver no longer needs the thought of the clutch as a
stimulus, for the left foot movement on the clutch has become
effectively linke