Speech is the use of thehuman voice as a medium forlanguage.Spoken language combinesvowel andconsonant sounds to form units of meaning likewords, which belong to a language'slexicon. There are many different intentionalspeech acts, such as informing, declaring,asking,persuading, directing; acts may vary in various aspects likeenunciation,intonation,loudness, andtempo to convey meaning. Individuals may also unintentionally communicate aspects of their social position through speech, such as sex, age, place of origin, physiological and mental condition, education, and experiences.
While normally used to facilitatecommunication with others, people may also use speech without the intent to communicate. Speech may nevertheless express emotions or desires; peopletalk to themselves sometimes in acts that are a development of what somepsychologists (e.g.,Lev Vygotsky) have maintained is the use of silent speech in aninterior monologue to vivify and organizecognition, sometimes in the momentary adoption of a dual persona as self addressing self as though addressing another person. Solo speech can be usedto memorize or to test one's memorization of things, and inprayer or inmeditation.
The evolutionaryorigin of speech is subject to debate and speculation. Whileanimals also communicate using vocalizations, and trained apes such asWashoe andKanzi can use simplesign language, no animals' vocalizations are articulated phonemically and syntactically, and do not constitute speech.
Although related to the more general problem of theorigin of language, theevolution of distinctively human speech capacities has become a distinct and in many ways separate area of scientific research.[2][3][4][5][6] The topic is a separate one because language is not necessarily spoken: it can equally bewritten orsigned. Speech is in this sense optional, although it is the default modality for language.
Monkeys, non-humanapes and humans, like many other animals, have evolved specialised mechanisms for producingsound for purposes of social communication.[7] On the other hand, no monkey or ape uses itstongue for such purposes.[8][9] The human species' unprecedented use of the tongue, lips and other moveable parts seems to place speech in a quite separate category, making its evolutionary emergence an intriguing theoretical challenge in the eyes of many scholars.[10]
Determining the timeline of human speech evolution is made additionally challenging by the lack of data in the fossil record. The humanvocal tract does not fossilize, and indirect evidence of vocal tract changes in hominid fossils has proven inconclusive.[10]
Speech production is an unconscious multi-step process by which thoughts are generated into spoken utterances. Production involves the unconscious mind selecting appropriate words and the appropriate form of those words from the lexicon and morphology, and the organization of those words through the syntax. Then, the phonetic properties of the words are retrieved and the sentence is articulated through the articulations associated with those phonetic properties.[11]
Inlinguistics,articulatory phonetics is the study of how the tongue, lips, jaw, vocal cords, and other speech organs are used to make sounds. Speech sounds are categorized bymanner of articulation andplace of articulation. Place of articulation refers to where in the neck or mouth the airstream is constricted. Manner of articulation refers to the manner in which the speech organs interact, such as how closely the air is restricted, what form of airstream is used (e.g.pulmonic, implosive, ejectives, and clicks), whether or not the vocal cords are vibrating, and whether the nasal cavity is opened to the airstream.[12] The concept is primarily used for the production ofconsonants, but can be used forvowels in qualities such asvoicing andnasalization. For any place of articulation, there may be several manners of articulation, and therefore severalhomorganic consonants.
Normal human speech is pulmonic, produced with pressure from thelungs, which createsphonation in theglottis in thelarynx, which is then modified by the vocal tract and mouth into different vowels and consonants. However humans can pronounce words without the use of the lungs and glottis inalaryngeal speech, of which there are three types:esophageal speech, pharyngeal speech and buccal speech (better known asDonald Duck talk).
Speech production is a complex activity, and as a consequence errors are common, especially in children. Speech errors come in many forms and are used to provide evidence to support hypotheses about the nature of speech.[13] As a result, speech errors are often used in the construction of models for language production andchild language acquisition. For example, the fact that children often make the error of over-regularizing the -ed past tense suffix in English (e.g. saying 'singed' instead of 'sang') shows that the regular forms are acquired earlier.[14][15] Speech errors associated with certain kinds of aphasia have been used to map certain components of speech onto the brain and see the relation between different aspects of production; for example, the difficulty ofexpressive aphasia patients in producing regular past-tense verbs, but not irregulars like 'sing-sang' has been used to demonstrate that regular inflected forms of a word are not individually stored in the lexicon, but produced from affixation to the base form.[16]
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 ofphonetics andphonology 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 understandspoken language. Research into speech perception also has applications in buildingcomputer systems that can recognize speech, as well as improving speech recognition for hearing- and language-impaired listeners.[17]
Speech perception iscategorical, in that people put the sounds they hear into categories rather than perceiving them as a spectrum. People are more likely to be able to hear differences in sounds across categorical boundaries than within them. A good example of this isvoice onset time (VOT), one aspect of the phonetic production of consonant sounds. For example, Hebrew speakers, who distinguish voiced /b/ from voiceless /p/, will more easily detect a change in VOT from -10 ( perceived as /b/ ) to 0 ( perceived as /p/ ) than a change in VOT from +10 to +20, or -10 to -20, despite this being an equally large change on the VOT spectrum.[18]
Most human children develop proto-speech babbling behaviors when they are four to six months old. Most will begin saying their first words at some point during the first year of life. Typical children progress through two or three word phrases before three years of age followed by short sentences by four years of age.[19]
In speech repetition, speech being heard is quickly turned from sensory input into motor instructions needed for its immediate or delayed vocal imitation (inphonological 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.[20]
Diseases and disorders of thebrain, includingalogia,aphasias,dysarthria,dystonia andspeech processing disorders, where impairedmotor planning, nerve transmission, phonological processing or perception of the message (as opposed to the actual sound) leads to poor speech production.
Hearing problems, such asotitis media with effusion, and listening problems,auditory processing disorders, can lead to phonological problems. In addition todysphasia,anomia and auditory processing disorder impede the quality of auditory perception, and therefore, expression. Those who aredeaf or hard of hearing may be considered to fall into this category.
Psychiatric disorders have been shown to change speech acoustic features, where for instance,fundamental frequency of voice (perceived as pitch) tends to be significantly lower inmajor depressive disorder than in healthy controls.[21] Therefore, speech is being investigated as a potential biomarker for mental health disorders.
Speech and language disorders can also result from stroke,[22] brain injury,[23] hearing loss,[24] developmental delay,[25] a cleft palate,[26] cerebral palsy,[27] or emotional issues.[28]
Speech-related diseases, disorders, and conditions can be treated by a speech-language pathologist (SLP) or speech therapist. SLPs assess levels of speech needs, make diagnoses based on the assessments, and then treat the diagnoses or address the needs.[29]
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 orexpressive aphasia, is characterized by difficulty in speech production where speech is slow and labored, function words are absent, and syntax is severely impaired, as intelegraphic speech. In expressive aphasia, speech comprehension is generally less affected except in the comprehension of grammatically complex sentences.[31] Wernicke's area is named afterCarl 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 had damage to the prefrontal cortex.[32] Damage to Wernicke's area produces Wernicke's orreceptive aphasia, which is characterized by relatively normal syntax and prosody but severe impairment in lexical access, resulting in poor comprehension and nonsensical orjargon speech.[31]
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.[33] Instead, multiple streams are involved in speech production and comprehension. Damage to the leftlateral 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.[34]Moreover, the circuits involved in human speech comprehension dynamically adapt with learning, for example, by becoming more efficient in terms of processing time when listening to familiar messages such as learned verses.[35]
Some non-human animals can produce sounds or gestures resembling those of a human language.[36] Several species or groups of animals have developedforms of communication which superficially resemble verbal language, however, these usually are not considered a language because they lack one or more of thedefining characteristics, e.g.grammar,syntax,recursion, anddisplacement. Researchers have been successful in teaching some animals to make gestures similar tosign language,[37][38] although whether this should be considered a language has been disputed.[39]
^Kelemen, G. (1963). Comparative anatomy and performance of the vocal organ in vertebrates. In R. Busnel (ed.),Acoustic behavior of animals. Amsterdam: Elsevier, pp. 489–521.
^Riede, T.; Bronson, E.; Hatzikirou, H.; Zuberbühler, K. (February 2006). "Multiple discontinuities in nonhuman vocal tracts – A reply".Journal of Human Evolution.50 (2):222–225.Bibcode:2006JHumE..50..222R.doi:10.1016/j.jhevol.2005.10.005.
^Catford, J.C.; Esling, J.H. (2006). "Articulatory Phonetics". In Brown, Keith (ed.).Encyclopedia of Language & Linguistics (2nd ed.). Amsterdam: Elsevier Science. pp. 425–42.
^Fromkin, Victoria (1973). "Introduction".Speech Errors as Linguistic Evidence. The Hague: Mouton. pp. 11–46.
^Nicoladis, Elena; Paradis, Johanne (2012). "Acquiring Regular and Irregular Past Tense Morphemes in English and French: Evidence From Bilingual Children".Language Learning.62 (1):170–97.doi:10.1111/j.1467-9922.2010.00628.x.
^Ullman, Michael T.; et al. (2005). "Neural correlates of lexicon and grammar: Evidence from the production,reading, and judgement of inflection in aphasia".Brain and Language.93 (2):185–238.doi:10.1016/j.bandl.2004.10.001.PMID15781306.S2CID14991615.
^Kennison, Shelia (2013).Introduction to Language Development. Los Angeles: Sage.
^Kishon-Rabin, Liat; Rotshtein, Shira; Taitelbaum, Riki (2002). "Underlying Mechanism for Categorical Perception: Tone-Onset Time and Voice-Onset Time Evidence of Hebrew Voicing".Journal of Basic and Clinical Physiology and Pharmacology.13 (2):117–34.doi:10.1515/jbcpp.2002.13.2.117.PMID16411426.S2CID9986779.
^Richards, Emma (June 2012). "Communication and swallowing problems after stroke".Nursing and Residential Care.14 (6):282–286.doi:10.12968/nrec.2012.14.6.282.
^Zasler, Nathan D.; Katz, Douglas I.; Zafonte, Ross D.; Arciniegas, David B.; Bullock, M. Ross; Kreutzer, Jeffrey S., eds. (2013).Brain injury medicine principles and practice (2nd ed.). New York: Demos Medical. pp. 1086–1104,1111–1117.ISBN9781617050572.
^Bauman-Waengler, Jacqueline (2011).Articulatory and phonological impairments: a clinical focus (4th ed., International ed.). Harlow: Pearson Education. pp. 378–385.ISBN9780132719957.
^Cross, Melanie (2011).Children with social, emotional and behavioural difficulties and communication problems: there is always a reason (2nd ed.). London: Jessica Kingsley Publishers.
^Kertesz, A. (2005). "Wernicke–Geschwind Model". In L. Nadel,Encyclopedia of cognitive science. Hoboken, NJ: Wiley.
^abHillis, 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 (ed.).Reader in the History of Aphasia: Fromsasi(Franz Gall to). Vol. 4. Amsterdam: John Benjamins Pub Co. pp. 69–89.ISBN978-90-272-1893-3.
^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. (eds.).The Perception of Speech: from sound to meaning. Oxford: Oxford University Press. pp. 193–217.ISBN978-0-19-956131-5.
^Hillix, William A.; Rumbaugh, Duane M. (2004), "Washoe, the First Signing Chimpanzee",Animal Bodies, Human Minds: Ape, Dolphin, and Parrot Language Skills, Springer US, pp. 69–85,doi:10.1007/978-1-4757-4512-2_5,ISBN978-1-4419-3400-0
