he right hand, and then on a sudden strikes
his own head (above the ear). The whole performance gave exactly the
impression of his having for the first time noticed that it is one
thing to strike oneself, one's own hard head, and another thing to
strike a foreign hard object (forty-first week). Even in the
thirteenth month the child often raps his head with his hand to try
the effect, and seems surprised at the hardness of the head. In the
sixteenth month he used not unfrequently to set the left thumb
against the left side of the head, and at the same time the right
thumb against the right side of the head, above the ears, with the
fingers spread, and to push at the same time, putting on a strange,
wondering expression of face, with wide-open eyes. This movement is
not imitated and not inherited, but invented. The child is doubtless
making experiments by means of it upon the holding of the head,
head-shaking, resistance of his own body, perhaps also upon the
management of the head, as at every thump of the thumbs against the
temporal bones a dull sound was heard. The objectivity of the
fingers was found out not much before this time by involuntary,
painful biting of them, for as late as the fifteenth month the child
bit his finger so that he cried out with pain. Pain is the most
efficient teacher in the learning of the difference between
subjective and objective.

Another important factor is the _perception of a change produced by
ones own activity_ in all sorts of familiar objects that can be
taken hold of in the neighborhood; and the most remarkable day, from
a psychogenetic point of view, in any case an extremely significant
day in the life of the infant, is the one in which he first
experiences the _connection of a movement executed by himself with a
sense-impression following upon it_. The noise that comes from the
tearing and crumpling of paper is as yet unknown to the child. He
discovers (in the fifth month) the fact that he himself in tearing
paper into smaller and smaller pieces has again and again the new
sound-sensation, and he repeats the experiment day by day and with a
strain of exertion until this connection has lost the charm of
novelty. At present there is not, indeed, as yet any clear insight
into the nexus of cause; but the child has now had the experience
that he can himself be the cause of a combined perception of sight
and sound regularly, to the extent that when he tears paper there
appears, on