of all kinds are reactions.

B. The stimulus that directly arouses a mental process is often
"central".

C. Brain activities of all sorts influence the muscles by way
of the motor area and the lower motor centers.

D. Brain action in skilled movement.

E. Brain action in speech.

F. Brain action in sensation.

G. Brain action in recognizing seen or heard objects.

H. Relations of reactions of different levels.

2. Define and illustrate these classes of stimuli:

A. Peripheral:

(1) External.

(2) Internal.

B. Central.

3. Show by a diagram how one cortical center arouses another.
Compare the diagram in Fig. 9, p. 37.

4. Facilitation of the patellar reflex or "knee jerk". Let your
subject sit with one leg hanging freely from the knee down. With
the edge of your hand strike the patellar tendon just below the
knee cap. (a) Compare the reflex movement so obtained with a
voluntary imitation by the subject. Which is the quicker and
briefer? (b) Apply a fairly strong auditory stimulus (a sudden
noise) a fraction of a second before the tap on the tendon, and see
whether the reflex response is reinforced, (c) Ask the subject to
clench his fists or grit his teeth, and tap the tendon as he does
so. Reinforcement? (d) Where is the reflex center for the patellar
reflex, and whence comes the reinforcing influence?

5. Construct a diagram showing the different centers and connections
involved in making the skilled movement of writing; and consider
what loss of function would result from destruction of each of the
centers.

REFERENCES

Herrick's _Introduction to Neurology_, 1918, Chapter XX, on the
"Functions of the Cerebrum".

Stile's _Nervous System and Its Conservation_, Chapters X, XI
and XII.

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CHAPTER IV

TENDENCIES TO REACTION

HOW MOTIVES INFLUENCE BEHAVIOR, AND HOW THEY FIT INTO A PSYCHOLOGY
WHICH SEEKS TO ANALYZE BEHAVIOR INTO REACTIONS.

One advantage of basing our psychology on _reactions_ is that it keeps
us "close to the ground", and prevents our discussions from sailing
off into the clouds of picturesque but fanciful interpretation.
Psychology is very apt to degenerate into a game of blowing bubbles,
unless we pin ourselves down to hard-headed ways of thinking. The
notion of a reaction is of great value here, just because it is so
hard-headed and concrete. Whenever we have any human