Vocal stimulation early in life and infant vocal responsiveness to mother vs. stranger: A curvilinear relationship

Abstract

Ape language research presents us with a worthy and successful example of realist bootstrapping of theorizing and experimentation. In the 1940s, the Hayeses set out without a definition of language, merely taking it that it appeared in the normal maturation of the normal human in normal circumstances and so might appear in a chimpanzee similarly placed. The Gardeners, noting the chimpanzee's limited vocalizing apparatus, tried to show that a chimpanzee would develop language in the same way as the human child if only the language were a sign language. Meshing with research by Premack and Terrace, recent work on fluent human signers of American Sign Language has shown that while chimpanzees can be led to use a gestural pidgin-vocabulary to manipulate and socialize, they in no way develop linguistically as the human infant signer does. In terms of homology, a case can be made that the signing chimpanzees have little improved on the Hayeses' chimpanzee, who eventually vocalized five English words. What this stretch of interaction between theory and experiment bears out is the autonomy of the formal linguistic apparatus from other conceptual and perceptual capacities that we undoubtedly share with our primate cogeners.