Boris Sidis,
The Foundations of Normal and Abnormal Psychology…
(1914
| notes)
“ The child, when standing up all by himself, does it hesitatingly; he shakes and trembles, as if occupying unsafe ground, or doing a difficult act; he looks around for support, stretches out his hands, asking the help of his parents or nurse, and if he does not get aid in time, begins to cry from fear and drops on all-fours. It is a difficult feat for him. Withdraw his attention from his performance, and in the first stages of his series of trials he drops helplessly to the ground. ”
