We applied a test of postural development to 13 infant Japanese monkeys (0 days-29 weeks of age).
The test originally devised for human infants consists of 11 sorts of techniques each of which induces the postural reaction as follows : Traction, Landau, Axillar, Vojta, Collis-Horizontal, : Collis-Vertical, Peiper, Sideways-Parachute, Forward-Parachute, Backward-Parachute and Hopping.
Longitudinal observations showed that the standard reactions and their development could be identified in infant Japanese monkeys.
Postural reactions of infants developed in four stages. The criteria distinguishing these stages were mainly based on the reactions of fore- and hind-limbs against the gravity. We could find common characteristics in reactions in spite of different inducing techniques.
First stage (0-3 days) : the flection of fore- and hind-limbs. Any reactions of the limbs were not induced which made it possible to support the body weight.
Second stage (3 days-4 weeks) : the extension of forelimbs but the flection of the hindlimbs. The elbow extended with the pronation of the forearm and dorsiflection of the wrist to support the body weight by the hand.
Third stage (4-12 weeks) : The extension of fore- and hind-limbs. The knee extended with the pronation of the foot. This reaction made it possible to support the body weight by the foot.
Fourth stage (12 weeks and thereafter) : stepping of the hindlimb. Stepping of the hindlimb was induced by Hopping.
According to our observations of spontaneous postures and locomotions in infants, new behavioral topographies; sitting, walking and so on, appeared at the transitive phases from one to the next stage of the postural reactions.
Development of postural reactions in infant monkeys was similar to those investigated in humans.
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