Abstract
In the present study, I investigated 15, 604 infants by means of a check list of approximately thirty items in order to find the standard tendency of the development of infants. For each observed item the development was shown by a percentile curve. The results, on the whole, corresponded with the already standardized tendency of infant development in Japan. During the period of infancy which is considered to be the first “twist” or distortion in the course of human development, there were found four representative phases in which several typical gross activities were observable. They are, namely, the first period (4.7mos.-5.8mos.), the second (7.9mos.-8.2mos.), the third (9.4mos.-10.2mos.), and the fourth period (11.0mos.-12.0mos.). It is hard to find an appropriate designation to characterize those periods. They take somewhat the forms of “plateaus” in the learning curve. The tendencies of those periods will be fully discussed in the next report.
