Acquisition and Testing of Gestural Signs in Four Young Chimpanzees

TLDR

Four chimpanzees were trained on ten American Sign Language signs, with acquisition measured by the minutes needed to achieve five consecutive unprompted correct responses, followed by a double‑blind test of nine signs. All four chimpanzees mastered every sign, though some signs were consistently easier and individual differences emerged in acquisition speed and test performance.

Abstract

Two male and two female chimpanzees were each taught ten signs of American Sign Language. The acquisition rates of the signs were compared on the basis of the number of minutes required in training to reach a criterion of five consecutive unprompted correct responses. After the ten signs had been acquired, the chimpanzees were tested in a double-blind procedure for nine of the signs. All four chimpanzees acquired all of the signs. Some signs were consistently easier to acquire than others, and individual differences between the four chimpanzees were found in the acquisition rates and tests.