Age Change in Learning Ability of Japanese Monkeys (Macaca Fuscata) Measured by the Transfer Index

To examine the developmental change in learning 26 Japanese monkeys at five ages, 1, 2, 3, 5, and over 7 years old, were given two sorts of discrimination-reversal problems differing in prereversal acquisition, one at 67% and the other at 80%. Transfer Index was estimated. With a shift in acquisition from 67% to 80%, the Transfer Indexes were maintained in the 1-, 2-, and 3-yr. groups but declined in the 5-yr. and the adult groups. The results suggest some critical point in learning by Japanese monkeys.