|Applied and experimental|
Speech is the vocalized form of communication based upon the syntactic combination of lexicals and names that are drawn from very large (usually about 1,000 different words) vocabularies. Each spoken word is created out of the phonetic combination of a limited set of vowel and consonant speech sound units (phonemes). These vocabularies, the syntax that structures them, and their sets of speech sound units differ, creating many thousands of different, and mutually unintelligible, human languages. Most human speakers are able to communicate in two or more of them, hence being polyglots. The vocal abilities that enable humans to produce speech also enable them to sing.
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. In addition to its use in communication, it is suggested by some psychologists such as Vygotsky that speech is internally used in 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 recreate them, which plays a key role in 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 animals also communicate with vocalizations. While none in the wild have compatibly large vocabularies, research upon the nonverbal abilities of language trained apes such as Washoe and Kanzi raises the possibility that they might have these capabilities. The origins of speech are unknown and subject to much debate and speculation.
In linguistics (articulatory phonetics), manner of articulation describes how the tongue, lips, jaw, vocal cords, and other speech organs used to produce sounds, make contact with each other. Often the concept is only used for the production of consonants. For any place of articulation, there may be several manners of articulation, and therefore several homorganic consonants.
Normal human speech is produced with pressure from the lungs, which creates phonation in the glottis in the larynx, which is then modified by the vocal tract into different vowels and consonants. However humans can pronounce words without the use of the lungs and glottis in alaryngeal speech, of which there are three types: esophageal speech, pharyngeal speech and buccal speech (better known as Donald Duck talk).
Speech perception refers to the processes by which humans can interpret and understand the sounds used in language. The study of speech perception is closely linked to the fields of phonetics and phonology in linguistics and cognitive psychology and perception in psychology. Research in speech perception seeks to understand how listeners recognize speech sounds and use this information to understand spoken language. Research into speech perception also has applications in building computer systems that can recognize speech, as well as improving speech recognition for hearing- and language-impaired listeners.
In speech repetition, speech being heard is quickly turned from sensory input into motor instructions needed for its immediate or delayed vocal imitation (in phonological memory). This type of mapping plays a key role in enabling children to expand their spoken vocabulary. Masur (1995) found that how often children repeat novel words versus those they already have in their lexicon is related to the size of their lexicon later on, with young children who repeat more novel words having a larger lexicon later in development. Speech repetition could help facilitate the acquisition of this larger lexicon.
Speech is a complex activity; as a result, errors are often made in speech. Speech errors have been analyzed by scientists to understand the nature of the processes involved in the production of speech.
Problems involving speech
There are several organic and psychological factors that can affect speech. Among these are:
- Diseases and disorders of the lungs or the vocal cords, including paralysis, respiratory infections (bronchitis), vocal fold nodules and cancers of the lungs and throat.
- Diseases and disorders of the brain, including alogia, aphasias, dysarthria, dystonia and speech processing disorders, where impaired motor planning, nerve transmission, phonological processing or perception of the message (as opposed to the actual sound) leads to poor speech production.
- Hearing problems, such as otitis media with effusion, and listening problems, auditory processing disorders, can lead to phonological problems.
- Articulatory problems, such as slurred speech, stuttering, lisping, cleft palate, ataxia, or nerve damage leading to problems in articulation. Tourette syndrome and tics can also affect speech. Various congenital and acquired tongue diseases can affect speech as can motor neuron disease.
- In addition to dysphasia, anomia and auditory processing disorder can impede the quality of auditory perception, and therefore, expression. Those who are Hard of Hearing or deaf may be considered to fall into this category.
The classical model
The classical or Wernicke-Geschwind model of the language system in the brain focusses on Broca's area in the inferior prefrontal cortex, and Wernicke's area in the posterior superior temporal gyrus on the dominant hemisphere of the brain (typically the left hemisphere for language). In this model, a linguistic auditory signal is first sent from the auditory cortex to Wernicke's area. The lexicon is accessed in Wernicke's area, and these words are sent via the arcuate fasciculus to Broca's area, where morphology, syntax, and instructions for articulation are generated. This is then sent from Broca's area to the motor cortex for articulation. 
Paul Broca identified an approximate region of the brain in 1861 which, when damaged in two of his patients, caused severe deficits in speech production, where his patients were unable to speak beyond a few monosyllabic words. This deficit, known as Broca's or expressive aphasia, is characterized by difficulty in speech production where speech is slow and labored, function words are absent, and syntax is severely impaired, as in telegraphic speech. In expressive aphasia, speech comprehension is generally less affected except in the comprehension of grammatically complex sentences. Wernicke's area is named after Carl Wernicke, who in 1874 proposed a connection between damage to the posterior area of the left superior temporal gyrus and aphasia, as he noted that not all aphasic patients had suffered damage to the prefrontal cortex. Damage to Wernicke's area produces Wernicke's or receptive aphasia, which is characterized by relatively normal syntax and prosody but severe impairment in lexical access, resulting in poor comprehension and nonsensical or jargon speech.
Modern models of the neurological systems behind linguistic comprehension and production recognize the importance of Broca's and Wernicke's areas, but are not limited to them nor solely to the left hemisphere. Instead, multiple streams are involved in speech production and comprehension. Damage to the left lateral sulcus has been connected with difficulty in processing and producing morphology and syntax, while lexical access and comprehension of irregular forms (e.g. eat-ate) remain unaffected.
- Freedom of speech
- Imagined speech
- Index of linguistics articles
- List of language disorders
- Spatial hearing loss
- Talking birds
- Tucker, G. Richard (1999). "A Global Perspective on Bilingualism and Bilingual Education." (PDF). Carnegie Mellon University. Retrieved 23 April 2012. (Archive)
- Kennison, Shelia (2013). Introduction to Language Development. Los Angeles: Sage.
- Masur, Elise (1995). "Infants' Early Verbal Imitation and Their Later Lexical Development". Merrill-Palmer Quarterly. 41 (3): 286–306.
- Kertesz, A. (2005). "Wernicke--GeschwindModel". In L. Nadel, Encyclopedia of cognitive science. Hoboken, NJ: Wiley.
- Hillis, A. E., & Caramazza, A. (2005). "Aphasia". In L. Nadel, Encyclopedia of cognitive science. Hoboken, NJ: Wiley.
- Wernicke K. (1995). "The aphasia symptom-complex: A psychological study on an anatomical basis (1875)". In Paul Eling. Reader in the History of Aphasia: From sasi(Franz Gall to). 4. Amsterdam: John Benjamins Pub Co. pp. 69–89. ISBN 90-272-1893-5.
- Tyler, Lorraine K.; Marslen-Wilson, William (2009). "Fronto-temporal brain systems supporting spoken language comprehension". In Moore, Brian C. J.; Tyler, Lorraine K.; Marslen-Wilson, William D. The Perception of Speech: from sound to meaning. Oxford: Oxford University Press. pp. 193–217. ISBN 978-0-19-956131-5.
- (French) Fitzpatrick, Élizabeth M. Apprendre à écouter et à parler. University of Ottawa Press, 2013. Available at Project MUSE.