n dendrites and end-brushes, forming synapses in the cortex,
and such minute structures make little impression on the total brain
weight.

While intelligence is related to the cerebrum as a whole, rather than
to any particular "intelligence center", there is some likelihood that
the special aptitudes are related to special parts of the cortex,
though it must be admitted that few aptitudes have as yet been
localized. The pretended localizations of phrenology are all wrong.
But we do know that each sense has its special cortical area, and that
adjacent to these sensory areas are portions of the cortex intimately
concerned in response to different classes of complex stimuli. Near
the auditory center the cortex is concerned in recognizing spoken
words, and in following music; near the visual center it is concerned
in recognizing printed words, in recognizing seen objects, in finding
one's way by the sense of sight, etc. These special aptitudes thus
have a fairly definite cortical localization, and possibly others have
also.

Examined microscopically, the cortex shows differences of structure in
different parts, and to the structural differences probably correspond
differences of function. Now it is practically impossible that such a
function as attention or memory should have any localized cortical
center, for these are general functions. The instincts are specialized
enough to have local centers, but none have so far been localized.
What has been localized is of the nature of special aptitudes.

{294}

EXERCISES

1. Outline the chapter.

2. Pick out the true statements from the following list:

(a) Man is the most intelligent of animals.

(b) Intelligence depends on the development of the cerebellum.

(c) It has not been found possible to use any single
performance as a reliable index of intelligence.

(d) Children of different mental ages may have the same IQ.

(e) A child with a mental age of 10 years can do all the tests
for 10 years and below, but none of those for the higher ages.

(f) The intelligence tests depend wholly on accurate response
and not at all on speed of reaction.

(g) If intelligence tests depended upon previous training, they
could not be measures of native intelligence.

(h) High correlation between the test scores of brothers and
sisters is a fact that tends to indicate the importance of
heredity in determining intelligence.