Using naturalistic utterances to investigate vocal communication processing and development in human and non-human primates

Humans and several non-human primates possess cortical regions that are most sensitive to vocalizations produced by their own kind (conspecifics). However, the use of speech and other broadly defined categories of behaviorally relevant natural sounds has led to many discrepancies regarding where voice-sensitivity occurs, and more generally the identification of cortical networks, "proto-networks" or protolanguage networks, and pathways that may be sensitive or selective for certain aspects of vocalization processing. In this prospective review we examine different approaches for exploring vocal communication processing, including pathways that may be, or become, specialized for conspecific utterances. In particular, we address the use of naturally produced non-stereotypical vocalizations (mimicry of other animal calls) as another category of vocalization for use with human and non-human primate auditory systems. We focus this review on two main themes, including progress and future ideas for studying vocalization processing in great apes (chimpanzees) and in very early stages of human development, including infants and fetuses. Advancing our understanding of the fundamental principles that govern the evolution and early development of cortical pathways for processing non-verbal communication utterances is expected to lead to better diagnoses and early intervention strategies in children with communication disorders, improve rehabilitation of communication disorders resulting from brain injury, and develop new strategies for intelligent hearing aid and implant design that can better enhance speech signals in noisy environments. This article is part of a Special Issue entitled "Communication Sounds and the Brain: New Directions and Perspectives".