Empirical evidence for the claim that the vocal theory of language origins and the gestural theory of language origins are not incompatible with one another

Abstract

The author argues about the implications of the evolution of motherese for the emergence of language in the human history, and it occurred in both the vocal mode and the manual mode, the fact indicating that the gestural theory of and the vocal theory of language origins are not incompatible with one another. It is a commonplace observation that hearing adults tend to modify their speech in an unusual and characteristic fashion when they address infants and young children. The available data indicate that motherese or infant-directed speech is a prevalent form of language input to hearing infants and that its salience for preverbal infants results both from the infant’s attentional responsiveness to certain sounds more readily than others and from the infant’s affective responsiveness to certain attributes of the auditory signal. In the signing behavior of deaf mothers when communicating with their deaf infants, a phenomenon quite analogous to motherese in maternal speech is observed. Concerning the aspect of linguistic input, moreover, there is evidence for the presence of predispositional preparedness in human infants to detect motherese characteristics equally in the manual mode and in the vocal mode. Such cognitive preparedness, in fact, serves as a basis on which sign language learning proceeds in deaf infants. One can seek its evolutionary origins in the rudimentary form of teaching behavior that occurs in the adult-infant interaction in nonhuman primates as well as in humans, by which the cross-generational transmission of parenting is made possible, including that in the deaf community.