A gestural form of human communication exists for the deaf in the form of sign language. Speech in some cultures has become the basis of a written language, often one that differs in its vocabulary, syntax and phonetics from its associated spoken one, a situation called diglossia. Speech in addition to its use in communication, it is suggested by some psychologists such as Vygotsky is internally used by mental processes to enhance and organize cognition in the form of an interior monologue.
Speech is researched in terms of the speech production and speech perception of the sounds used in vocal language. Other research topics concern speech repetition, the ability to map heard spoken words into the vocalizations needed to recreated that plays a key role in the vocabulary expansion in children and speech errors. Several academic disciplines study these including acoustics, psychology, speech pathology, linguistics, cognitive science, communication studies, otolaryngology and computer science. Another area of research is how the human brain in its different areas such as the Broca's area and Wernicke's area underlies speech.
It is controversial how far human speech is unique in that other animals also communicate with vocalizations. While none in the