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Speech is the vocalized form of human communication. It is based upon the syntactic combination of lexicals and names that are drawn from very large (usually about 10,000 different words) vocabularies. Each spoken word is created out of the phonetic combination of a limited set of vowel and consonant speech sound units. These vocabularies, the syntax which structures them, and their set of speech sound units differ, creating the existence of many thousands of different types of mutually unintelligible human languages. Most human speakers (polyglots) are able to communicate in two or more of them. The vocal abilities that enable humans to produce speech also provide humans with the ability 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. 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 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, and other speech organs are involved in making a sound make contact. Often the concept is only used for the production of consonants. For any place of articulation, there may be several manners, and therefore several homorganic consonants.
Normal human speech is produced with pulmonary pressure provided by the lungs which creates phonation in the glottis in the larynx that 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 are able to 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 human listeners recognize speech sounds and use this information to understand spoken language. Speech research has applications in building computer systems that can recognize speech, as well as improving speech recognition for hearing- and language-impaired listeners.
Aristotle is generally credited with developing the basics of the system of rhetoric, influencing the development of rhetorical theory from ancient through modern times. The Rhetoric is regarded by most rhetoricians as "the most important single work on persuasion ever written”. The study of rhetoric was contested in classical Greece: on the one side were the Sophists, and on the other side were Socrates, Plato, and Aristotle. The trio saw rhetoric and poetry as tools that were too often used to manipulate others by manipulating emotion and omitting facts. They particularly accused the sophists, including Gorgias and Isocrates, of this manipulation. Plato, particularly, laid the blame for the arrest and the death of Socrates at the feet of sophistical rhetoric. In stark contrast to the emotional rhetoric and poetry of the sophists was a rhetoric grounded in philosophy and the pursuit of enlightenment. According to Aristotle, logic is concerned with reasoning to reach scientific certainty while dialectic and rhetoric are concerned with probability and, thus, are the branches of philosophy that are best suited to human affairs. Dialectic is a tool for philosophical debate; it is a means for skilled audiences to test probable knowledge in order to learn. Conversely, rhetoric is a tool for practical debate; it is a means for persuading a general audience using probable knowledge to resolve practical issues. Dialectic and rhetoric create a partnership for a system of persuasion based on knowledge instead of upon manipulation and omission.
It is based upon the syntactic combination of lexical and names that are drawn from very large vocabularies. Each spoken word is created out of the phonetic combination of a limited set of vowel and consonant speech sound units. These vocabularies, the syntax which structures them and their set of speech sound units differ, creating the existence of many thousands of different types of mutually unintelligible human languages. Most human speakers (polyglots) are able to communicate in two or more of them. <referenceshttp://www.sparknotes.com/biography/aristotle/section9.==References==
Spoken vocalizations are quickly turned from sensory inputs into motor instructions needed for their immediate or delayed (in phonological memory) vocal imitation. This occurs independently of speech perception. This mapping plays a key role in enabling children to expand their spoken vocabulary and hence the ability of human language to transmit across generations.
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 stuttering, lisping, cleft palate, ataxia, or nerve damage leading to problems in articulation. Tourette syndrome and tics can also affect speech. Many speakers also have a slur in their voice
- 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.
Brain physiology 
Two areas of the cerebral cortex are necessary for speech. Broca's area, named after its discoverer, French neurologist Paul Broca (1824-1880), is in the frontal lobe, usually on the left, near the motor cortex controlling muscles of the lips, jaws, soft palate and vocal cords. When damaged by a stroke or injury, comprehension is unaffected but speech is slow and labored and the sufferer will talk in "telegramese". Wernicke's area, discovered in 1874 by German neurologist Carl Wernicke (1848-1904), lies to the back of the temporal lobe, again, usually on the left, near the areas receiving auditory and visual information. Damage to it destroys comprehension - the sufferer speaks fluently but nonsensically. Some researchers have explored the connections between brain physiology, neuroscience, and other elements of physiology to that of communication. Communibiology first proposed by Beatty and McCroskey address these issues and presents a set of specific axioms about these phenomena.
See also 
- Imagined speech
- Index of linguistics articles
- Spatial hearing loss
- Talking birds
- Tucker, G. Richard (1999). "A Global Perspective on Bilingualism and Bilingual Education.". Carnegie Mellon University. Retrieved 23 April 2012.
- Masur, E. F. (1995). "Infants' early verbal imitation and their later lexical development". Merrill-Palmer Quarterly 41 (3): 286–306. OCLC 89395784.
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- Acoustic measures of speech, www.speech-therapy-information-and-resources.com
- CiteULike "Speech and Language Pathology" research paper sharing group, www.citeulike.org
- Speaking captured by real-time MRI, YouTube