months used to perform in its sleep imitative movements which had made a
strong impression while awake--e.g., blowing; this shows that dreaming
occurs at least as early as the first year. After the first year
imitative movements are more readily learned than before.

Shaking the head as a sign of negation was found by Preyer, as by other
observers, to be instinctive, and he adopts Darwin's explanation of the
fact--viz., that the satisfied suckling in refusing the breast must
needs move its head from side to side. In the seventeenth month the
child exhibited a definite act of intelligent adjustment, for, desiring
to reach a toy down from a press, it drew a traveling-bag from another
part of the room to stand upon. We mention this incident because it
exhibits the same level of mental development as that of Cuvier's orang,
which, on desiring to reach an object off a high shelf, drew a chair
below the shelf to stand upon. Anger was expressed in the tenth month,
shame and pride in the nineteenth.

Between the tenth and eleventh month the first perception of causality
was observed. Thus on the three hundred and nineteenth day the child was
beating on a plate with a spoon and accidentally found that the sound
was damped by placing the other hand upon the plate; it then changed its
hands and repeated the experiment. Similarly at eleven months it struck
a spoon upon a newspaper, and changed hands to see if this would modify
the sound. In some children, however, the perception of causality to
this extent occurs earlier. The present writer has seen a boy when
exactly eight months old deriving much pleasure from striking the
keys of a piano, and clearly showing that he understood the action of
striking the keys to be the antecedent required for the production of
the sound.