Sign languages (also known as signed languages) are that use the visual-manual modality to convey meaning. Sign languages are expressed through manual articulations in combination with non-manual elements. Sign languages are full-fledged natural languages with their own grammar and lexicon. Sign languages are not universal and they are not mutually intelligible with each other, although there are also striking similarities among sign languages.
Linguists consider both spoken and signed communication to be types of natural language, meaning that both emerged through an abstract, protracted aging process and evolved over time without meticulous planning. Sign language should not be confused with body language, a type of nonverbal communication.
Wherever communities of deaf people exist, sign languages have developed as handy means of communication and they form the core of local . Although signing is used primarily by the deaf and Hearing loss, it is also used by hearing individuals, such as those unable to physically speak, those who have trouble with spoken language due to a disability or condition (augmentative and alternative communication), or those with deaf family members, such as children of deaf adults.
It is unclear how many sign languages currently exist worldwide. Each country generally has its own native sign language, and some have more than one. The 2013 edition of Ethnologue lists 137 sign languages. Some sign languages have obtained some form of legal recognition, while others have no status at all.Wheatley, Mark & Annika Pabsch (2012). Sign Language Legislation in the European Union - Edition II. European Union of the Deaf.
Linguists distinguish natural sign languages from other systems that are precursors to them or derived from them, such as invented manual codes for spoken languages, home sign, "baby sign", and signs learned by non-human primates.
Until the 19th century, most of what is known about historical sign languages is limited to the manual alphabets (fingerspelling systems) that were invented to facilitate transfer of words from a spoken language to a sign language, rather than documentation of the language itself. Pedro Ponce de León (1520–1584) is said to have developed the first manual alphabet.
In 1620, Juan Pablo Bonet published Reducción de las letras y arte para enseñar a hablar a los mudos (‘Reduction of letters and art for teaching mute people to speak’) in Madrid.Pablo Bonet, J. de (1620) Reduction de las letras y Arte para enseñar á ablar los Mudos. Ed. Abarca de Angulo, Madrid, ejemplar facsímil accesible en la , online (spanish) scan of book, held at University of Sevilla, Spain It is considered the first modern treatise of sign language phonetics, setting out a method of oral education for deaf people and a manual alphabet.
In Britain, manual alphabets were also in use for a number of purposes, such as secret communication,Wilkins, John (1641). Mercury, the Swift and Silent Messenger. The book is a work on cryptography, and fingerspelling was referred to as one method of "secret discoursing, by signes and gestures". Wilkins gave an example of such a system: "Let the tops of the fingers signifie the five vowels; the middle parts, the first five consonants; the bottomes of them, the five next consonants; the spaces betwixt the fingers the foure next. One finger laid on the side of the hand may signifie T. Two fingers V the consonant; Three W. The little finger crossed X. The wrist Y. The middle of the hand Z." (1641:116-117) public speaking, or communication by deaf people.John Bulwer's "Chirologia: or the natural language of the hand.", published in 1644, London, mentions that alphabets are in use by deaf people, although Bulwer presents a different system which is focused on public speaking. In 1648, John Bulwer described "Master Babington", a deaf man proficient in the use of a manual alphabet, "contryved on the joynts of his fingers", whose wife could converse with him easily, even in the dark through the use of tactile signing.Bulwer, J. (1648) Philocopus, or the Deaf and Dumbe Mans Friend, London: Humphrey and Moseley.
In 1680, George Dalgarno published Didascalocophus, or, The deaf and dumb mans tutor,Dalgarno, George. Didascalocophus, or, The deaf and dumb mans tutor. Oxford: Halton, 1680. in which he presented his own method of deaf education, including an "arthrological" alphabet, where letters are indicated by pointing to different joints of the fingers and palm of the left hand. Arthrological systems had been in use by hearing people for some time;See Wilkins (1641) above. Wilkins was aware that the systems he describes are old, and refers to Bede's account of Roman and Greek finger alphabets. some have speculated that they can be traced to early Ogham manual alphabets.Montgomery, G. "The Ancient Origins of Sign Handshapes" Sign Language Studies 2(3) (2002): 322-334.
The of this alphabet have survived in the contemporary alphabets used in British Sign Language, Auslan and New Zealand Sign Language. The earliest known printed pictures of consonants of the modern two-handed alphabet appeared in 1698 with Digiti Lingua (Latin for Language or of the Finger), a pamphlet by an anonymous author who was himself unable to speak.Moser H.M., O'Neill J.J., Oyer H.J., Wolfe S.M., Abernathy E.A., and Schowe, B.M. "Historical Aspects of Manual Communication" Journal of Speech and Hearing Disorders 25 (1960) 145-151.
and Hay, A. and Lee, R. A Pictorial History of the evolution of the British Manual Alphabet (British Deaf History Society Publications: Middlesex, 2004) He suggested that the manual alphabet could also be used by mutes, for silence and secrecy, or purely for entertainment. Nine of its letters can be traced to earlier alphabets, and 17 letters of the modern two-handed alphabet can be found among the two sets of 26 handshapes depicted.
Charles de La Fin published a book in 1692 describing an alphabetic system where pointing to a body part represented the first letter of the part (e.g. Brow=B), and vowels were located on the fingertips as with the other British systems.Charles de La Fin (1692). Sermo mirabilis, or, The silent language whereby one may learn ... how to impart his mind to his friend, in any language ... being a wonderful art kept secret for several ages in Padua, and now published only to the wise and prudent ... London, Printed for Tho. Salusbury... and sold by Randal Taylor... 1692. He described such codes for both English and Latin.
By 1720, the British manual alphabet had found more or less its present form.Daniel Defoe (1720). "The Life and Adventures of Mr. Duncan Campbell" Descendants of this alphabet have been used by deaf communities (or at least in classrooms) in former British colonies India, Australia, New Zealand, Uganda and South Africa, as well as the republics and provinces of the former Yugoslavia, Grand Cayman Island in the Caribbean, Indonesia, Norway, Germany and the United States.
Frenchman Charles-Michel de l'Épée published his manual alphabet in the 18th century, which has survived basically unchanged in France and North America until the present time. In 1755, Abbé de l'Épée founded the first school for deaf children in Paris; Laurent Clerc was arguably its most famous graduate. Clerc went to the United States with Thomas Hopkins Gallaudet to found the American School for the Deaf in Hartford, Connecticut, in 1817.Canlas (2006). Gallaudet's son, Edward Miner Gallaudet, founded a school for the deaf in 1857 in Washington, D.C., which in 1864 became the National Deaf-Mute College. Now called Gallaudet University, it is still the only liberal arts university for deaf people in the world.
Sign languages generally do not have any linguistic relation to the spoken languages of the lands in which they arise. The correlation between sign and spoken languages is complex and varies depending on the country more than the spoken language. For example, the US, Canada, UK, Australia and New Zealand all have English as their dominant language, but American Sign Language (ASL), used in the US and English-speaking Canada, is derived from French Sign Language whereas the other three countries use varieties of [[British, Australian and New Zealand Sign Language|BANZSL]], which is unrelated to ASL. Similarly, the sign languages of Spain and Mexico are very different, despite Spanish being the national language in each country, and the sign language used in [[Bolivia]] is based on ASL rather than any sign language that is used in any other Spanish-speaking country. Variations also arise within a 'national' sign language which don't necessarily correspond to dialect differences in the national spoken language; rather, they can usually be correlated to the geographic location of residential schools for the deaf.Lucas, Ceil, Robert Bayley and [[Clayton Valli]]. 2001. Sociolinguistic Variation in American Sign Language. Washington, DC: Gallaudet University Press.Lucas, Ceil, Bayley, Robert, Clayton Valli. 2003. What's Your Sign for PIZZA? An Introduction to Variation in American Sign Language. Washington, DC: Gallaudet University Press.
International Sign, formerly known as Gestuno, is used mainly at international deaf events such as the Deaflympics and meetings of the World Federation of the Deaf. While recent studies claim that International Sign is a kind of a pidgin, they conclude that it is more complex than a typical pidgin and indeed is more like a full sign language.Cf. Supalla, Ted & Rebecca Webb (1995). "The grammar of international sign: A new look at pidgin languages." In: Emmorey, Karen & Judy Reilly (eds). Language, gesture, and space. (International Conference on Theoretical Issues in Sign Language Research) Hillsdale, N.J.: Erlbaum, pp. 333–352; McKee R. & J. Napier J. (2002). "Interpreting in International Sign Pidgin: an analysis." Journal of Sign Language Linguistics 5(1).
While the more commonly used term is International Sign, it is sometimes referred to as Gestuno,Rubino, F., Hayhurst, A., and Guejlman, J. (1975). Gestuno. International sign language of the deaf. Carlisle: British Deaf Association. or International Sign PidginMcKee R., Napier J. (2002) "Interpreting in International Sign Pidgin: an analysis." Journal of Sign Language Linguistics 5(1). and International Gesture (IG).Bar-Tzur, David (2002). International gesture: Principles and gestures website
Moody, W. (1987). International gesture. In J. V. Van Cleve (ed.), "Gallaudet encyclopedia of deaf people and deafness", Vol 3 S-Z, Index. NewYork: McGraw-Hill Book Company Inc. International Sign is a term used by the World Federation of the Deaf and other international organisations.
Sign languages are not mime—in other words, signs are conventional, often arbitrary and do not necessarily have a visual relationship to their referent, much as most spoken language is not onomatopoeic. While iconicity is more systematic and widespread in sign languages than in spoken ones, the difference is not categorical.Johnston (1989). The visual modality allows the human preference for close connections between form and meaning, present but suppressed in spoken languages, to be more fully expressed.Taub (2001). This does not mean that sign languages are a visual rendition of a spoken language. They have complex of their own and can be used to discuss any topic, from the simple and concrete to the lofty and abstract.
Sign languages, like spoken languages, organize elementary, meaningless units called phonemes into meaningful semantic units. (These were once called , from the Greek word for "hand", in the case of sign languages, by analogy to the , from Greek for "voice", of spoken languages, but now also called phonemes, since the function is the same.) This is often called duality of patterning. As in spoken languages, these meaningless units are represented as (combinations of) features, although often also crude distinctions are made in terms of handshape (or handform), orientation, location (or place of articulation), movement, and non-manual expression.Fabian Bross (2016). “Chereme” . In: Hall, T. A. Pompino-Marschall, B. (ed.): Dictionaries of Linguistics and Communication Science. Volume: Phonetics and Phonology. Berlin, New York: Mouton de Gruyter. More generally, both sign and spoken languages share the characteristics that linguists have found in all natural human languages, such as transitoriness, semanticity, arbitrariness, productivity, and cultural transmission.
Common linguistic features of many sign languages are the occurrence of classifiers constructions, a high degree of inflection by means of changes of movement, and a topic-comment syntax. More than spoken languages, sign languages can convey meaning by simultaneous means, e.g. by the use of space, two manual articulators, and the signer's face and body. Though there is still much discussion on the topic of iconicity in sign languages, classifiers are generally considered to be highly iconic, as these complex constructions "function as predicates that may express any or all of the following: motion, position, stative-descriptive, or handling information".Emmorey, K. (2002). Language, cognition and the brain: Insights from sign language research. Mahwah, NJ: Lawrence Erlbaum Associates. It needs to be noted that the term classifier is not used by everyone working on these constructions. Across the field of sign language linguistics the same constructions are also referred with other terms.
Today, linguists study sign languages as true languages, part of the field of linguistics. However, the category "sign languages" was not added to the Linguistic Bibliography / Bibliographie Linguistique until the 1988 volume,p. 970-972. Linguistic Bibliography for the Year 1988. Leiden, Netherlands:Brill. when it appeared with 39 entries.
As a sign language develops, it sometimes borrows elements from spoken languages, just as all languages borrow from other languages that they are in contact with. Sign languages vary in how and how much they borrow from spoken languages. In many sign languages, a manual alphabet (fingerspelling) may be used in signed communication to borrow a word from a spoken language, by spelling out the letters. This is most commonly used for proper names of people and places; it is also used in some languages for concepts for which no sign is available at that moment, particularly if the people involved are to some extent bilingual in the spoken language. Fingerspelling can sometimes be a source of new signs, such as initialized signs, in which the handshape represents the first letter of a spoken word with the same meaning.
On the whole, though, sign languages are independent of spoken languages and follow their own paths of development. For example, British Sign Language (BSL) and American Sign Language (ASL) are quite different and mutually unintelligible, even though the hearing people of the United Kingdom and the United States share the same spoken language. The grammars of sign languages do not usually resemble those of spoken languages used in the same geographical area; in fact, in terms of syntax, ASL shares more with spoken Japanese grammar than it does with English.Nakamura (1995).
Similarly, countries which use a single spoken language throughout may have two or more sign languages, or an area that contains more than one spoken language might use only one sign language. South Africa, which has 11 official spoken languages and a similar number of other widely used spoken languages, is a good example of this. It has only one sign language with two variants due to its history of having two major educational institutions for the deaf which have served different geographic areas of the country.
One way in which many sign languages take advantage of the spatial nature of the language is through the use of classifiers. Classifiers allow a signer to spatially show a referent's type, size, shape, movement, or extent.
The large focus on the possibility of simultaneity in sign languages in contrast to spoken languages is sometimes exaggerated, though. The use of two manual articulators is subject to motor constraints, resulting in a large extent of symmetryBattison, Robbin (1978). Lexical Borrowing in American Sign Language. Silver Spring, MD: Linstok Press. or signing with one articulator only. Further, sign languages, just like spoken languages, depend on linear sequencing of signs to form sentences; the greater use of simultaneity is mostly seen in the morphology (internal structure of individual signs).
At the lexical level, signs can be lexically specified for non-manual elements in addition to the manual articulation. For instance, facial expressions may accompany verbs of emotion, as in the sign for angry in Czech Sign Language. Non-manual elements may also be lexically contrastive. For example, in ASL (American Sign Language), facial components distinguish some signs from other signs. An example is the sign translated as not yet, which requires that the tongue touch the lower lip and that the head rotate from side to side, in addition to the manual part of the sign. Without these features the sign would be interpreted as late.Liddell, Scott K. (2003). Grammar, Gesture, and Meaning in American Sign Language. Cambridge: Cambridge University Press. , which are (parts of) spoken words accompanying lexical signs, can also be contrastive, as in the manually identical signs for doctor and battery in Sign Language of the Netherlands.
While the content of a signed sentence is produced manually, many grammatical functions are produced non-manually (i.e., with the face and the torso).Fabian Bross & Daniel Hole: Scope-taking strategies in German Sign Language . In: Glossa. A Journal of General Linguistics, 2(1): 76. 1-30 Such functions include questions, negation, relative clauses and topicalization. ASL and BSL use similar non-manual marking for yes/no questions, for example. They are shown through raised eyebrows and a forward head tilt.Baker, Charlotte, and Dennis Cokely (1980). American Sign Language: A teacher's resource text on grammar and culture. Silver Spring, MD: T.J. Publishers.Sutton-Spence, Rachel, and Bencie Woll (1998). The linguistics of British Sign Language. Cambridge: Cambridge University Press.
Some adjectival and adverbial information is conveyed through non-manual elements, but what these elements are varies from language to language. For instance, in ASL a slightly open mouth with the tongue relaxed and visible in the corner of the mouth means 'carelessly', but a similar non-manual in BSL means 'boring' or 'unpleasant'.
Discourse functions such as turn taking are largely regulated through head movement and eye gaze. Since the addressee in a signed conversation must be watching the signer, a signer can avoid letting the other person have a turn by not looking at them, or can indicate that the other person may have a turn by making eye contact.Baker, Charlotte (1977). Regulators and turn-taking in American Sign Language discourse, in Lynn Friedman, On the other hand: New perspectives on American Sign Language. New York: Academic Press
In 1978, Psychologist Roger Brown was one of the first to suggest that the properties of ASL give it a clear advantage in terms of learning and memory.Brown, R. (1978). Why Are Signed Languages Easier to Learn than Spoken Languages? Part Two. Bulletin of the American Academy of Arts and Sciences, 32(3), 25. In his study, Brown found that when a group of six hearing children were taught signs that had high levels of iconic mapping they were significantly more likely to recall the signs in a later memory task than another group of six children that were taught signs that had little or no iconic properties. In contrast to Brown, linguists Elissa Newport and Richard Meier found that iconicity "appears to have virtually no impact on the acquisition of American Sign Language".
A central task for the pioneers of sign language linguistics was trying to prove that ASL was a real language and not merely a collection of gestures or "English on the hands." One of the prevailing beliefs at this time was that 'real languages' must consist of an arbitrary relationship between form and meaning. Thus, if ASL consisted of signs that had iconic form-meaning relationship, it could not be considered a real language. As a result, iconicity as a whole was largely neglected in research of sign languages.
The cognitive linguistics perspective rejects a more traditional definition of iconicity as a relationship between linguistic form and a concrete, real-world referent. Rather it is a set of selected correspondences between the form and meaning of a sign.Taub (2001) In this view, iconicity is grounded in a language user's mental representation ("construal" in cognitive grammar). It is defined as a fully grammatical and central aspect of a sign language rather than a peripheral phenomenon.Wilcox (2004)
The cognitive linguistics perspective allows for some signs to be fully iconic or partially iconic given the number of correspondences between the possible parameters of form and meaning.Wilcox (2000) In this way, the Israeli Sign Language (ISL) sign for "ask" has parts of its form that are iconic ("movement away from the mouth" means "something coming from the mouth"), and parts that are arbitrary (the handshape, and the orientation).Meir (2010)
Many signs have metaphoric mappings as well as iconic or metonymic ones. For these signs there are three way correspondences between a form, a concrete source and an abstract target meaning. The ASL sign LEARN has this three way correspondence. The abstract target meaning is "learning". The concrete source is putting objects into the head from books. The form is a grasping hand moving from an open palm to the forehead. The iconic correspondence is between form and concrete source. The metaphorical correspondence is between concrete source and abstract target meaning. Because the concrete source is connected to two correspondences linguistics refer to metaphorical signs as "double mapped".
]] Although sign languages have emerged naturally in deaf communities alongside or among spoken languages, they are unrelated to spoken languages and have different grammatical structures at their core.
Sign languages may be classified by how they arise.
In non-signing communities, home sign is not a full language, but closer to a pidgin. Home sign is amorphous and generally idiosyncratic to a particular family, where a deaf child does not have contact with other deaf children and is not educated in sign. Such systems are not generally passed on from one generation to the next. Where they are passed on, creole genesis would be expected to occur, resulting in a full language. However, home sign may also be closer to full language in communities where the hearing population has a gestural mode of language; examples include various Australian Aboriginal sign languages and gestural systems across West Africa, such as Mofu-Gudur in Cameroon.
A village sign language is a local indigenous language that typically arises over several generations in a relatively insular community with a high incidence of deafness, and is used both by the deaf and by a significant portion of the hearing community, who have deaf family and friends.
Deaf-community sign languages, on the other hand, arise where deaf people come together to form their own communities. These include school sign, such as Nicaraguan Sign Language, which develop in the student bodies of deaf schools which do not use sign as a language of instruction, as well as community languages such as Bamako Sign Language, which arise where generally uneducated deaf people congregate in urban centers for employment. At first, Deaf-community sign languages are not generally known by the hearing population, in many cases not even by close family members. However, they may grow, in some cases becoming a language of instruction and receiving official recognition, as in the case of ASL.
Both contrast with speech taboo languages such as the various Aboriginal Australian sign languages, which are developed by the hearing community and only used secondarily by the deaf. It is doubtful whether most of these are languages in their own right, rather than manual codes of spoken languages, though a few such as Yolngu Sign Language are independent of any particular spoken language. Hearing people may also develop sign to communicate with speakers of other languages, as in Plains Indian Sign Language; this was a contact signing system or pidgin that was evidently not used by deaf people in the Plains nations, though it presumably influenced home sign.
Language contact and creole language is common in the development of sign languages, making clear family classifications difficult – it is often unclear whether lexical similarity is due to borrowing or a common parent language, or whether there was one or several parent languages, such as several village languages merging into a Deaf-community language. Contact occurs between sign languages, between sign and spoken languages (contact sign, a kind of pidgin), and between sign languages and gesture used by the broader community. One author has speculated that Adamorobe Sign Language, a village sign language of Ghana, may be related to the "gestural trade jargon used in the markets throughout West Africa", in vocabulary and including prosody and phonetics.Frishberg (1987). See also the classification of Henri Wittmann (1991) for the general issue of jargons as prototypes in sign language genesis.
The only comprehensive classification along these lines going beyond a simple listing of languages dates back to 1991.Henri Wittmann (1991). The classification is said to be typological satisfying Jakobson's condition of genetic interpretability. The classification is based on the 69 sign languages from the 1988 edition of Ethnologue that were known at the time of the 1989 conference on sign languages in Montreal and 11 more languages the author added after the conference.
|+ Wittmann classification of sign languages
language ! Primary
group ! Auxiliary
language ! Auxiliary
|DGS-derived||1 or 2||–||–||–|
In his classification, the author distinguishes between primary and auxiliary sign languagesWittmann adds that this taxonomic criterion is not really applicable with any scientific rigor: Auxiliary sign languages, to the extent that they are full-fledged natural languages (and therefore included in his survey) at all, are mostly used by the deaf as well, and some primary sign languages (such as ASL and Adamorobe Sign Language) have acquired auxiliary usages. as well as between single languages and names that are thought to refer to more than one language.Wittmann includes in this class Australian Aboriginal sign languages (at least 14 different languages), Monastic sign language, Thai Hill-Country sign languages (possibly including languages in Vietnam and Laos), and Sri Lankan sign languages (14 deaf schools with different sign languages). The prototype-A class of languages includes all those sign languages that seemingly cannot be derived from any other language.These are Adamorobe Sign Language, Armenian Sign Language, Australian Aboriginal sign languages, Hindu mudra, the Monastic sign languages, Martha's Vineyard Sign Language, Plains Indian Sign Language, Urubú-Kaapor Sign Language, Chinese Sign Language, Indo-Pakistani Sign Language (Pakistani SL is said to be R, but Indian SL to be A, though they are the same language), Japanese Sign Language, and maybe the various Thai Hill-Country sign languages, French Sign Language, Lyons Sign Language, and Nohya Maya Sign Language. Wittmann also includes, bizarrely, Chinese characters and Egyptian hieroglyphs. Prototype-R languages are languages that are remotely modelled on a prototype-A language (in many cases thought to have been French Sign Language) by a process Kroeber (1940) called "stimulus diffusion".These are Providencia Island, Kod Tangan Bahasa Malaysia (manually signed Malay), German, Ecuadoran, Salvadoran, Gestuno, Indo-Pakistani (Pakistani SL is said to be R, but Indian SL to be A, though they are the same language), Kenyan, Brazilian, Spanish, Nepali (with possible admixture), Penang, Rennellese, Saudi, the various Sri Lankan sign languages, and perhaps BSL, Peruvian, Tijuana (spurious), Venezuelan, and Nicaraguan sign languages. The families of BANZSL, DGS, JSL, LSF (and possibly LSG) were the products of creolization and relexification of prototype languages.Wittmann's references on the subject, besides his own work on creolization and relexification in spoken languages, include papers such as Fischer (1974, 1978), Deuchar (1987) and Judy Kegl's pre-1991 work on creolization in sign languages. Creolization is seen as enriching overt morphology in sign languages, as compared to reducing overt morphology in spoken languages.Wittmann's explanation for this is that models of acquisition and transmission for sign languages are not based on any typical parent-child relation model of direct transmission which is inducive to variation and change to a greater extent. He notes that sign creoles are much more common than vocal creoles and that we can't know on how many successive creolizations prototype-A sign languages are based prior to their historicity.
Sign languages vary in word-order typology. For example, Austrian Sign Language, Japanese Sign Language and Indo-Pakistani Sign Language are Subject-object-verb while ASL is Subject-verb-object. Influence from the surrounding spoken languages is not improbable.
Sign languages tend to be incorporating classifier languages, where a classifier handshape representing the object is incorporated into those transitive verbs which allow such modification. For a similar group of intransitive verbs (especially motion verbs), it is the subject which is incorporated. Only in a very few sign languages (for instance Japanese Sign Language) are agents ever incorporated. in this way, since subjects of intransitives are treated similarly to objects of transitives, incorporation in sign languages can be said to follow an ergative pattern.
BrentariBrentari, Diane (1998): A prosodic model of sign language phonology. Cambridge, Massachusetts: MIT Press; cited in Hohenberger (2007) on p. 349Brentari, Diane (2002): Modality differences in sign language phonology and morphophonemics. In: Richard P. Meier, Kearsy Cormier, and David Quinto-Pozos (eds.), 35–36; cited in Hohenberger (2007) on p. 349 classifies sign languages as a whole group determined by the medium of communication (visual instead of auditory) as one group with the features monosyllabic and polymorphemic. That means, that one syllable (i.e. one word, one sign) can express several morphemes, e.g., subject and object of a verb determine the direction of the verb's movement (inflection).
Another aspect of typology that has been studied in sign languages is their systems for cardinal numbers.Ulrike Zeshan, Cesar Ernesto Escobedo Delgado, Hasan Dikyuva, Sibaji Panda, and Connie de Vos. 2013. Cardinal numerals in rural sign languages: Approaching cross-modal typology. Linguistic Typology 17: 357–396. Typologically significant differences have been found between sign languages.
The Critical Period hypothesis suggests that language, spoken or signed, is more easily acquired as a child at a young age versus an adult because of the plasticity of the child's brain. In a study done at the University of McGill, they found that American Sign Language users who acquired the language natively (from birth) performed better when asked to copy videos of ASL sentences than ASL users who acquired the language later in life. They also found that there are differences in the grammatical morphology of ASL sentences between the two groups, all suggesting that there is a very important critical period in learning signed languages.
The acquisition of non-manual features follows an interesting pattern: When a word that always has a particular non-manual feature associated with it (such as a wh- question word) is learned, the non-manual aspects are attached to the word but don't have the flexibility associated with adult use. At a certain point, the non-manual features are dropped and the word is produced with no facial expression. After a few months, the non-manuals reappear, this time being used the way adult signers would use them.
Several ways to represent sign languages in written form have been developed.
So far, there is no consensus regarding the written form of sign language. Except for SignWriting, none are widely used. Maria Galea writes that SignWriting "is becoming widespread, uncontainable and untraceable. In the same way that works written in and about a well developed writing system such as the Latin script, the time has arrived where SW is so widespread, that it is impossible in the same way to list all works that have been produced using this writing system and that have been written about this writing system." In 2015, the Federal University of Santa Catarina accepted a dissertation written in Brazilian Sign Language using Sutton SignWriting for a master's degree in linguistics. The dissertation " The Writing of Grammatical Non-Manual Expressions in Sentences in LIBRAS Using the SignWriting System" by João Paulo Ampessan states that "the data indicate the need for non-manual usage in writing sign language".
One example of sign language variation in the Deaf community is Black ASL. This sign language was developed in the Black Deaf community as a variant during the American era of segregation and racism, where young Black Deaf students were forced to attend separate schools than their white Deaf peers.McCaskill, C. (2011). The hidden treasure of Black ASL: its history and structure. Washington, D.C.: Gallaudet University Press.
Many Australian Aboriginal sign languages arose in a context of extensive speech taboos, such as during mourning and initiation rites. They are or were especially highly developed among the Warlpiri, Warumungu people, Dieri, Kaytetye people, Arrernte people, and Warlmanpa, and are based on their respective spoken languages.
A pidgin sign language arose among tribes of American Indians in the Great Plains region of North America (see Plains Indian Sign Language). It was used by hearing people to communicate among tribes with different spoken , as well as by deaf people. There are especially users today among the Crow tribe, Cheyenne, and Arapaho. Unlike Australian Aboriginal sign languages, it shares the spatial grammar of deaf sign languages. In the 1500s, a Spanish expeditionary, Cabeza de Vaca, observed natives in the western part of modern-day Florida using sign language, and in the mid-16th century Coronado mentioned that communication with the Tonkawa using signs was possible without a translator. Whether or not these gesture systems reached the stage at which they could properly be called languages is still up for debate. There are estimates indicating that as many as 2% of Native Americans are seriously or completely deaf, a rate more than twice the national average.
Signs may also be used by hearing people for manual communication in secret situations, such as hunting, in noisy environments, underwater, through windows or at a distance.
The Internet now allows deaf people to talk via a video link, either with a special-purpose videophone designed for use with sign language or with "off-the-shelf" videotelephony designed for use with broadband and an ordinary computer webcam. The special videophones that are designed for sign language communication may provide better quality than 'off-the-shelf' services and may use data compression methods specifically designed to maximize the intelligibility of sign languages. Some advanced equipment enables a person to remotely control the other person's video camera, in order to zoom in and out or to point the camera better to understand the signing.
The interpretation flow is normally between a sign language and a spoken language that are customarily used in the same country, such as French Sign Language (LSF) and spoken French in France, Spanish Sign Language (LSE) to spoken Spanish in Spain, British Sign Language (BSL) and spoken English in the U.K., and American Sign Language (ASL) and spoken English in the US and most of anglophone Canada (since BSL and ASL are distinct sign languages both used in English-speaking countries), etc. Sign language interpreters who can translate between signed and spoken languages that are not normally paired (such as between LSE and English), are also available, albeit less frequently.
With recent developments in artificial intelligence in computer science, some recent deep learning based machine translation algorithms have been developed which automatically translate short videos containing sign language sentences (often simple sentence consists of only one clause) directly to written language.
However, VRI cannot be used for situations in which all parties are speaking via telephone alone. With video relay service (VRS), the sign language user, the interpreter, and the hearing person are in three separate locations, thus allowing the two clients to talk to each other on the phone through the interpreter.
In traditional analogue broadcasting, many programmes are repeated, often in the early hours of the morning, with the signer present rather than have them appear at the main broadcast time. This is due to the distraction they cause to those not wishing to see the signer. On the BBC, many programmes that broadcast late at night or early in the morning are signed. Some emerging television technologies allow the viewer to turn the signer on and off in a similar manner to subtitles and closed captioning.
Legal requirements covering sign language on television vary from country to country. In the United Kingdom, the Broadcasting Act 1996 addressed the requirements for blind and deaf viewers, but has since been replaced by the Communications Act 2003.
This is in contrast to hearing children who grow up with Deaf parents, who generally acquire the full sign language natively, the same as Deaf children of Deaf parents.
Home sign arises due to the absence of any other way to communicate. Within the span of a single lifetime and without the support or feedback of a community, the child naturally invents signs to help meet his or her communication needs, and may even develop a few grammatical rules for combining short sequences of signs. Still, this kind of system is inadequate for the intellectual development of a child and it comes nowhere near meeting the standards linguists use to describe a complete language. No type of home sign is recognized as a full language.The one possible exception to this is Rennellese Sign Language, which has the ISO 639-3 code rsi. It only ever had one deaf user, and thus appears to have been a home sign system that was mistakenly-accepted into the ISO 639-3 standard. It has been proposed for deletion from the standard. ()