# Sign language in the brain

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[Sign language](/source/Sign_language) refers to any natural language which uses visual gestures produced by the hands and body language to express meaning. The brain's left side is the dominant side utilized for producing and understanding sign language, just as it is for speech.[1] In 1861, Paul Broca studied patients with the ability to understand spoken languages but the inability to produce them. The damaged area was named [Broca's area](/source/Broca's_area), and located in the left hemisphere’s inferior frontal gyrus ([Brodmann areas](/source/Brodmann_area) 44, 45). Soon after, in 1874, Carl Wernicke studied patients with the reverse deficits: patients could produce spoken language, but could not comprehend it. The damaged area was named [Wernicke's area](/source/Wernicke's_area), and is located in the left hemisphere’s posterior superior temporal gyrus ([Brodmann area](/source/Brodmann_area) 22).

Signers with damage in [Broca's area](/source/Broca's_area) have problems producing signs. Those with damage in the [Wernicke's area](/source/Wernicke's_area) (left hemisphere) in the temporal lobe of the brain have problems comprehending signed languages. Early on, it was noted that Broca’s area was near the part of the motor cortex controlling the face and mouth. Likewise, Wernicke's area was near the auditory cortex. These motor and auditory areas are important in spoken language processing and production, but the connection to signed languages had yet to be uncovered. For this reason, the left hemisphere was described as the verbal hemisphere, with the right hemisphere deemed to be responsible for spatial tasks. This criterion and classification was used to denounce signed languages as not equal to spoken language until it was widely agreed upon that due to the similarities in cortical connectivity they are linguistically and cognitively equivalent.

In the 1980s research on deaf patients with left hemisphere stroke were examined to explore the brains connection with signed languages. The left perisylvian region was discovered to be functionally critical for language, spoken and signed.[1][2] Its location near several key auditory processing regions led to the belief that [language processing](/source/Language_processing_in_the_brain) required auditory input and was used to discredit signed languages as "real languages."[2] This research opened the doorway for linguistic analysis and further research on signed languages. Signed languages, like spoken languages, are highly structured linguistic systems; they have their own sets of phonological, morphological and syntactic characteristics. Despite some differences between spoken and signed languages, the associated brain areas share a lot in common.[3]

Figure 1. Schematic of the ascending auditory pathway

## How the brain processes auditory information

One main structure for hearing is the [cochlea](/source/Cochlea), a tiny coiled structure within the ear (shown in Figure 2).[4] This is one of several structures that can be damaged to cause hearing loss. When sound waves enter the ear, they cause a vibration of the eardrum. This vibration causes the [ossicles](/source/Ossicles) of the ear to move, causing a depression of the [oval window](/source/Oval_window). This depression causes waves in the fluid of the cochlea which initiates movement of the [basilar membrane](/source/Basilar_membrane). Different sections of the basilar membrane are responsible for responding to different types of sound, with that specific sound’s wave reaching a peak at the responsible part of the basilar membrane. This process is what transforms the sound into neural activity via [hair cell](/source/Hair_cell) receptors. These receptors have stereocilia that cause a release of neurotransmitter onto the [vestibulocochlear nerve](/source/Vestibulocochlear_nerve) when moved.

The vestibulocochlear nerve synapses in [superior medulla](/source/Superior_medullary_velum) using cochlear nuclei.[5] This is considered the beginning of the ascending auditory pathway (shown in Figure 1). The cochlear nuclei then send information to the [superior olivary nucleus](/source/Superior_olivary_complex) to initiate the brain’s process of interpreting and combining information. The brain is able to localize sound by understanding the differences in sounds’ timing and intensities in each ear.[5] This information continues on to the [inferior colliculus](/source/Inferior_colliculus), which is important for the integration of a majority of ascending auditory information. The inferior colliculus sends this information to the [medial geniculate nucleus](/source/Medial_geniculate_nucleus) within the [thalamus](/source/Thalamus). The thalamus finally projects the information received to the [auditory cortex](/source/Auditory_cortex), which is housed in the [temporal lobe](/source/Temporal_lobe).

Figure 2. Schematic of the ear and internal structures

## Hemispheric similarities and differences between spoken and signed languages

Both the left and right hemisphere have brain structures associated with spoken and signed languages. Spoken and signed languages both depend on the same cortical substrate.[2] This shows that the left hemisphere is responsible for processing all facets of language, not just speech. The neural organization underlying sign language abilities, however, has more in common with that of spoken language than it does with the neural organization underlying visuospatial processing, which is processed dominantly in the right hemisphere.[2] Those patients with left hemisphere damage (LHD), in areas ranging from the frontal lobe to the occipital lobe, exhibited both Broca’s and Wernicke’s aphasia symptoms. Patients performed poorly on many language-based tasks such as comprehending signs and sentences and fluently signing. Similar to hearing patients’ “slips of the tongue” after LHD, deaf LHD patients experienced [paraphasias](/source/Paraphasia), or “slips of the hand.” These slips of the hand usually involve an incorrect hand shape in the correct location and with the correct movement, similar to a hearing patient substituting “bline” or “gine” for “fine.”[6] Some right hemisphere damage does lead to disruptions in sign languages, however. The topographical use of signing space is often imprecise in patients with RHD; the relation between the location of hands in signing space and the location of objects in physical space is often impaired. Rather than being misunderstood, however, subjects and objects in a sentence may simply be placed incorrectly relative to the other subjects and objects in a sentence, like saying “the pencil is in the book” rather than, “the pencil is on top of the book.”[6] Around the time of the experiment, theories began to float around the community that there may be an unexplained involvement of the right hemisphere in signed languages not seen in spoken languages. These theories were also adopted by signed language linguists and further imaging studies and neuropsychological testing confirmed the presence of activity in the right hemisphere.[7] Prior right hemisphere studies on spoken languages has led to prevailing theories in its role in [discourse cohesion](/source/Cohesion_(linguistics)) and [prosody](/source/Prosody_(linguistics)). The right hemisphere has been proposed to assist in detection, processing and discrimination of visual movement.[2] The right hemisphere has also been shown to play a role in the perception of body movements and positions.[2] All of these right hemisphere features are more prominent for signed languages than spoken languages, hence the argument that signed languages engage the right hemisphere more than spoken languages.

As brain imaging technology such as [EEG](/source/Electroencephalography) became more developed and commonplace, it was eventually applied to sign language comprehension. Using EEG to record event-related potentials can correlate specific brain activity to language processing in real time. Previous application of [ERP](/source/Event-related_potential) on hearing patients showed neural activity in the left hemisphere related to syntactic errors.[2] When electrodes are hooked up to deaf native signers, similar syntactic anomalies associated with an event-related potential were recorded across both left and right hemisphere. This shows that syntactic processing for American Sign Language (ASL) is not [lateralized](/source/Lateralization_of_brain_function) to the left hemisphere.[2]

When communicating in their respective languages, similar brain regions are activated for both deaf and hearing subjects with a few exceptions. During the processing of auditory stimuli for spoken languages there is detectable activity within Broca's Area, Wernicke's Area, the angular gyrus, dorsolateral prefrontal cortex, and superior temporal sulcus.[8] Right hemisphere activity was detectable in less than 50% of trials for hearing subjects reciting English sentences. When deaf subjects were tasked with reading English, none of the left hemisphere structures seen with hearing subjects were visible.[8] Deaf subjects also displayed obvious middle and posterior temporal-parietal activation within the right hemisphere.[8] When hearing subjects were presented various signs designed to evoke emotion within native signers, there was no clear changes in brain activity in traditional language processing centers. Brain activity of deaf native signers when processing signs was similar to activity of hearing subjects processing English. However, processing of ASL extensively recruited right hemisphere structures including significant activation of the entire superior temporal lobe, the angular region, and inferior prefrontal cortex. Since native hearing signers also exhibited this right hemisphere activation when processing ASL, it has been proposed that this right hemisphere activation is due to the temporal visuospatial decoding necessary to process signed languages.[8]

In a similar study published in 2017, deaf individuals who use French Sign Language were studied during processing French Sign Language and written French. During the processes of each of the languages, there was bilateral activation in the occipital lobes, in the temporal lobes near the superior temporal sulcus, and in the frontal gyri.[9] The processing of sign language showed stronger activation in both occipital lobes, both posterior temporal lobes, and in the thalamus bilaterally. It also showed strong activation particularly in structures in the right hemisphere: the superior temporal sulcus, the fusiform gyrus, and the inferior frontal gyrus.[9] Opposed to processing sign language, when the individuals processed written French there was strong activation bilaterally and in the left hemisphere. The areas that showed bilateral activation were the inferior parietal lobes, fusiform gyri, and Brodmann Area 44, among others. The areas lateralized to the left hemisphere were the calcarine and fusiform gyrus, specifically at the location for [visual word form](/source/Visual_word_form_area).[9]

## Neurological differences between deaf and hearing groups

It is thought that there are significant neuroanatomical differences among congenitally deaf humans versus those who become deaf later in life.[10] Therefore, it is widely thought that research into the differences in connections and projections of neurons in deaf humans must block into two groups—congenitally deaf and deaf after birth. Structural brain imaging has commonly shown white matter volume of the auditory cortices differs between deaf and hearing subjects, regardless of the first language learned.[10] Deaf humans are thought to have a larger ratio of gray matter to white matter in certain auditory cortices, such as left and right [Heschl's gyrus](/source/Transverse_temporal_gyrus) and [Superior Temporal gyrus](/source/Superior_temporal_gyrus).[11] This heightened ratio is thought to exist due to less overall white matter in Heschl's gyrus and the Superior Temoral gyrus among deaf humans. Overall, the auditory cortices of deaf humans have an increased gray-white matter ratio as a result of the lack of auditory stimuli which is commonly thought to lead to less myelination and fewer projections to and from the auditory cortices.[11]

It has been thought that congenitally deaf people could provide insight into brain plasticity; the decreased auditory connectivity and brain volume for auditory processing provides an opportunity for enhancement in the visual cortices which are of greater importance to deaf humans.[12] The [Calcarine sulcus](/source/Calcarine_sulcus) acts as the hub for the Primary Visual Cortex in humans. Congenitally deaf humans have measurably higher volume of Calcarine cortex than hearing humans.[12] The increased volume and size of visual cortices of deaf individuals can lead to heightened visual processing. Deaf humans have demonstrated, via event-related potential, an increased sensitivity and reactivity to new visual stimuli—evidence of brain plasticity leading to behavioral enhancement.[13]

## Differences between signers and non-signers

In one experiment published in 1992, visual [mental imagery](/source/Mental_image) was studied in ASL signers—deaf and hearing—and hearing non-signers. These hearing signers were born to deaf parents, and ASL was their first language. Another aspect looked at in this study was the difference between native signers and those who learned sign language at a later age. In this experiment, native signers are considered deaf individuals who were born to deaf parents and therefore started absorbing the language in infancy. The other deaf signers' primary language is sign language, but they did not learn it until between the ages of two and sixteen.[14]

In the experiment of generating simple and complex images, deaf individuals were the quickest, followed by hearing signers and then hearing non-signers. This was expected; however, looking at a chart of the results, the hearing signers performed almost identically, in regards to the simple and complex images, to the deaf signers but just more slowly.[14] The hearing non-signers were right on track in following behind on the simple image, but their reaction time was vastly longer.[14] At least in this area, experience with a visual-spatial language provides quicker reaction times.

The results are consistent with abilities recruited for processing sign language being enhanced in the brain, compared to those abilities in non-signers. A couple of things the subjects were tested on were [mental rotation](/source/Mental_rotation) and mirror reversals. Signers had an advantage in mirror reversals, but there was no difference between signers and non-signers performing mental rotation. Because of these results, it may not be true to say that signers have a better ability to transform images, but the ability may be in rotating images. Because of this experiment, the cause of enhanced abilities was questioned to be because of auditory deprivation or because of using a visual-spatial language. Hearing signers who learned sign language as a first language may be the key to answering this question.[14]

## Beneficial uses of sign language

While sign language is mostly used by people who are deaf, hard of hearing, or in close relationships with people that are deaf or hard of hearing, sign language can be beneficial for other conditions that cause difficulties with communicating using verbal language. These disorders can include issues with articulation, fluency, and voice.[15]

**[Apraxia of speech](/source/Apraxia_of_speech)**

This is a disorder that affects the brain's ability to plan the movements involved in speech.[16] In this disorder, the person cognitively knows what they want to say but is not able to produce that thought verbally. Apraxia of speech can be either acquired or present from birth. Acquired apraxia is due to damage in parts of the brain that are used for speech production, and the causes of apraxia from birth are not clear.

Some symptoms of apraxia are:

- Distortion of sounds (such as vowels)

- Inconsistent errors in speech

- Errors in tone, stress, or rhythm

**[Dysarthria](/source/Dysarthria)**

This is a disorder that is a result of either weakness in the muscles that are used for speech production or there is a decrease in the ability to control those muscles.[17] Some common causes of dysarthria are nervous system disorders or other disorders that can cause paralysis in the face, tongue, and throat.

Some symptoms of dysarthria are:

- Slurred or slow speech

- Inappropriate volume

- Rapid speech

- Abnormal speech rhythm

- Monotone speech

- Difficulty moving tongue or muscles in the face

**[Aphasia](/source/Aphasia)**

This is a disorder that impacts the way a person comprehends, speaks, and writes language. Aphasia usually is a result of traumatic head injury or stroke, but can have other causes such as tumors or progressive diseases.[18] There are several types of aphasia, with the two most popular being Broca’s Aphasia and Wernicke’s Aphasia. The different types of aphasia all have different impacts on the comprehension and production of language.

Some symptoms of aphasia are:

- Short or incomplete sentences

- Incorrect substitutions of words

- Unrecognizable words

- Difficulty finding words

- Not understanding what is being read

**Dysphonia**

This is a disorder of the voice and includes two different types. Hypofunctional dysphonia is due to closure of vocal cords or vocal folds being incomplete, whereas hyperfunctional dysphonia is due to overuse of laryngeal muscles.[19]

Some symptoms of dysphonia are:

- Breathy, hoarse or rough voice

- Voice instability

- Voice fatigue

## References

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[1][2]

v t e Sign language List of sign languages List by number of signers Language families[a] Sign languages by family Australian Aboriginal (multiple families)[c] Diyari Djingili Eltye eltyarrenke Iltyeme iltyeme Jaralde Kalkutungu Miriwoong Mudburra Pitha Pitha Rdaka rdaka Umpila Far North Queensland Warlmanpa Warluwara Warramunga Worora Kinship Yan-nhaŋu Yir Yoront Yolŋu Western Desert Kartutjarra Manjiljarra Ngaatjatjarra Zendath Kesign Meriam Western Torres Strait Islander Arab (Ishaaric) Egyptian Kuwaiti Libyan Qatari Unified Yemeni Iraqi– Levantine Iraqi Levantine Jordanian Lebanese Palestinian Syrian Possible Emirati Saudi Omani Chinese Sign Chinese (CSL/ZGS) Shanghai Hong Kong (HKSL) Macau Chilean-Paraguayan- Uruguayan Sign Chilean (LSCh) Paraguayan- Uruguayan Sign Paraguay (LSPY) Uruguay (LSU) Francosign Algerian (LSA) Swiss-German (DSGS) Estonian (Eesti viipekeel) Irish (ISL) Australian-Irish Brazilian (Libras) Lithuanian Catalan (LSC) Valencian (LSV) French (LSF) Old French[c] Romanian (LSR) American (ASLic) American (ASL) Black ASL (BASL) Protactile Bolivian Burmese Yangon Mandalay Cambodian Costa Rican Dominican Guyanese Jamaican Malaysian (BIM) Panamanian Filipino (FSL) Puerto Rican (PRSL) Singapore (SgSL) Indonesian (Nusantaric) Indonesian (Bisindo) Jakarta Yogyakarta Francophone African (Françafrosign) Ethiopian Chadian Ghanaian Guinean Bamako (LaSiMa) Moroccan Nigerian Sierra Leonean Mixed, Hand Talk Oneida (OSL) Mixed, Hoailona ʻŌlelo Creole Hawaiʻi Sign Language (CHSL) Mixed, French (LSF) Greek (ΕΝΓ/ENG) Cypriot (ΚΝΓ/KNG) Quebec (LSQ) Austro- Hungarian Czech (ČZJ) Hungarian (Magyar Jelnyev) Austrian (ÖGS) Slovak (SPJ) Ukrainian (УЖМ/USL) Russian Sign Azerbaijani (AİD) Bulgarian (БЖЕ) Georgian Kazakh-Russian (KSL/KRSL) Latvian (LSL) Mongolian Russian (РЖЯ) Yugoslavic Sign Croatian (HZJ) Kosovar Serbian Slovenian Yugoslav (YSL) Dutch Sign Dutch (NGT) Gambian Italian Sign Italian (LIS) Tunisian (TSL) Mexican Sign Mexican (LSM) Honduran (LESHO) Old Belgian Flemish (VGT) French Belgian (LSFB) Danish (Tegnic) Malagasy Icelandic (Táknmál) Norwegian (Tegnspråk) Danish (Tegnsprog) Faroese (Teknmál) Viet-Thai Hai Phong Hanoi Ho Chi Minh Thai (TSL/MSTSL) Hand Talk Great Basin Northeast Plains Sign Talk Southeast Southwest Mixed, American (ASL) Oneida (OSL) Plateau A'aninin Kalispel Ktunaxa (ʾa·qanⱡiⱡⱡitnam) Nesilextcl'n Shuswap (Secwepemcékst) Sqeliz Indo-Pakistani Sign Bangalore-Madras Beluchistan Bengali Bombay Calcutta Delhi Nepali North West Frontier Province Punjab-Sindh Japanese Sign Japanese (JSL/Nihon Shuwa) Korean (KSL/Hanguk Sueo) Taiwanese (TSL/Taiwan Shouyu) Kentish[c] Old Kentish Chilmark Martha's Vineyard (MVSL) Maya (Meemul Tziij / Meemul Ch'aab'al) Highland Maya Yucatec Chicán Nohkop Nohya Trascorral Cepeda Peraza NW Eurosign BANZSL Auslan Papua New Guinean (PNGSL) British (BSL) Northern Ireland (NISL) Fijian (FSL) Maritime (MSL) New Zealand (NZSL) Samoan South African (SASL) Swedish Sign Eritrean (EriSL) Finland-Swedish (FinSSL) Portuguese (LGP) Cape Verdian (LGC) São Tomé and Príncipean (LGSTP) Swedish (Teckenspråk) Finnish (Viittomakieli) German Sign German (DGS) Polish (PJM) Israeli (Shassi) Original Thai Sign Chiangmai Hai Phong Old Bangkok Paget Gorman Namibian (NSL) Providencia– Cayman Sign Providence Island (Provisle) Old Cayman (Guyanese) Isolates Afghan Akure (AkSL) Al-Sayyid Bedouin (ABSL) Albanian (AlbSL) Albarradas Sign Language Alipur Argentine (LSA) Armenian Caucasian (Harsneren)[c] Bay Islands Belizean Berbey Bhutanese Bouakako (LaSiBo) Bribri Brunca Bura Carhuahuaran Cena Central Taurus (CTSL/OTİD) Chatino Chiriqui Cuban (LSC) Dogon/Douentza Ecuadorian (LSEC) Enga Ghandruk Ghardaia (AJSL) Guatemalan (Lensegua) Guinea-Bissau Henniker[c] Hausa (HSL/Magannar Hannu) Hawaiʻi (Hoailona ʻŌlelo) Creole HSL Ibokun (IbSL) Inuit Inuit Uukturausingit (IUR) Greenlandic (Ussersuataarneq) Jhankot Jumla Ka'apor Kajana Kafr Qasim Kailge Kata Kolok Kenyan (KSL/LAK) Somali (SSL) Keresan Pueblo (KPISL/Keresign) Kisindo Jamaican Country (KS/Konchri Sain) Macedonian Magajin Gari (MgSL) Malawian Maltese (LSM) Mardin Maroua Maunabudhuk–Bodhe Mauritian (MSL) M'bour Mehek Miyakubo Shuwa Burkina (Mossi) Mount Avejaha Mozambican Naga Navajo/Diné Family Nicaraguan (ISN) Old Costa Rican Orocovis (LSOR) Ottoman (Seraglio/Harem) Ban Khor (Pasa kidd) Penang Persian (Esharani) Peruvian (LSP) Inmaculada Qahveh Khaneh Rennellese[c] Rossel Island Rwandan (AKR/AMR) Sandy River Valley[c] Salvadoran (LESSA) Sawmill Sinasina (SSSL) Sivia South Rupununi Spanish (LSE) Tebul Terena Tibetan (Bökyi lagda) Trinidad and Tobago (TTSL) Turkish (TİD) Ugandan (USL) Venezuelan (LSV/VSL) Wanib West African Adamorobe (AdaSL/Mumu kasa) Bura (Burasl) Mofu-Gudur Nanabin (NanabinSL) Yoruban (YSL) Zambian (ZSL) Other groupings Amami Shuwa languages Ethiopian languages Laotian languages Rwandan languages Sri Lankan languages Sudanese languages (~150)[b] Tanzanian languages (7+)[b] Zimsign languages International Sign Village languages By region[a] Sign languages by region Africa Algeria Algerian Ghardaia Cameroon Maroua Cape Verde Cape Verdian (LGC) Ghana Adamorobe (AdaSL / Mumu kasa) Nanabin Ivory Coast Bouakako (LaSiBo) Kenya Kenyan Malawi Malawian Mali Bamako (LaSiMa) Berbey Tebul Mozambique Mozambican Nigeria Akure (AkSL) Bura Hausa (Magannar Hannu) Ibokun (IbSL) Magajin Gari (MgSL) Rwanda Rwandan (Amarenga) São Tomé and Príncipe São Tomé and Príncipean (LGSTP) Senegal Mbour Somalia, Somaliland & Djibouti Somali South Africa South African Tanzania Tanzanian Uganda Ugandan Zambia Zambian Asia Bengal Bengali Cambodia Cambodian China Chinese Hong Kong Hong Kong (HKSL) India Alipur Bengali Indo-Pakistani Naga Indonesia Indonesian Kata Kolok (Benkala, Balinese) Iran Iranian (Esharani) Qahveh Khaneh Iraq Iraqi Kurdish Israel Al-Sayyid Bedouin Ghardaia Israeli Kafr Qasem Japan Japanese Koniya Miyakubo Korea Korean Kazakhstan Kazakh-Russian Laos Laotian Malaysia Malaysian Penang Selangor Maldives Maldives Mongolia Mongolian Nepal Ghandruk Jhankot Jumla Maunabudhuk–Bodhe Nepalese Philippines Filipino Saudi Arabia Saudi Singapore Singapore Sri Lanka Sri Lankan Taiwan Taiwanese Tajikistan Russian Tibet Tibetan (Bökyi lagda) Thailand Old Bangkok Chiangmai Thai Ban Khor (Pasa kidd) Vietnam Vietnamese Europe Armenia Armenian Austria Austrian Azerbaijan Azerbaijani Belgium Flemish French Belgian United Kingdom British Croatia Croatian Denmark Danish Faroese (Teknmál) Estonia Estonian Finland Finnish France Ghardaia French Lyons Georgia Georgian Germany German Greece Greek Hungary Hungarian Iceland Icelandic Ireland Irish Italy Italian Kosovo Yugoslav (Kosovar) Latvia Latvian Lithuania Lithuanian Moldova Russian Netherlands Dutch North Macedonia Macedonian Northern Ireland Northern Ireland Norway Norwegian Poland Polish Portugal Portuguese Russia Russian Slovenia Slovenian Spain Catalan Spanish Valencian Sweden Swedish Switzerland Swiss-German Turkey Central Taurus (CTSL/OTİD) Mardin Turkish Ukraine Ukrainian North and Central America Belize Belizean Canada American (ASL) Black ASL Protactile Hand Talk Oneida (OSL) Plateau Inuit (IUR) Maritime (MSL) Sawmill Quebec Cayman Old Cayman Costa Rica Bribri Brunca Old Costa Rican New Costa Rican Cuba Cuban Greenland Greenlandic (Ussersuataarneq) Guatemala Guatemalan Mayan Haiti Haitian Honduras Bay Islands Honduran Mexico Albarradas Chatino Mayan Mexican Nicaragua Nicaraguan Panama Chiriqui Panamanian Puerto Rico (USA) American (ASL) Puerto Rican Orocovis El Salvador Salvadoran (LESSO) Old Salvadoran United States American (ASL) Black ASL Protactile Hand Talk Oneida (OSL) Plateau Henniker Keresan (Keresign) Martha's Vineyard Navajo Family Sandy River Valley Sawmill Oceania Australia Akitiri (Eltye eltyarrenke) Arrernte (Iltyeme iltyeme) Auslan Australian-Irish Manjiljarra Mudbura (Mudburra) Ngada Umpila Far North Queensland Warlmanpa Warlpiri (Rdaka rdaka) Warumungu (Warramunga) Western Desert Western Torres Strait Islander Yir Yoront Yolŋu Hawaii (USA) Hawaiʻan (Haoilona ʻŌlelo) New Zealand New Zealand (NZSL) Papua New Guinea Enga Kailge Mehek Mount Avejaha Papua New Guinean (PNGSL) Rossel Island Sinasina Wanib Samoa and American Samoa Samoan South America Argentina Argentine (LSA) Bolivia Bolivian Brazil Brazilian (Libras) Cena Ka'apor South Rupununi Terena Chile Chilean Colombia Colombian Provisle Ecuador Ecuadorian Guyana Guyanese South Rupununi Paraguay Paraguayan Peru Carhuahuaran Inmaculada Peruvian Sivia Suriname Kajana Uruguay Uruguayan Venezuela Venezuelan International International Sign Makaton Monastic Signalong ASL Grammar Idioms Literature Profanity Name signs Extinct languages Chilmark Diyari Jaralde Kalkutungu Henniker Sign Language Martha's Vineyard Old French Old Kent Plateau Sign Language Pitha Pitha Sandy River Valley Sign Language Warluwara Linguistics Grammar (ASL) Bimodal bilingualism Phonology (ASL) Handshape / Location / Orientation / Movement / Expression Mouthing Nonmanual feature Sign names Home sign Fingerspelling American British (two-handed) Catalan Chilean Esperanto French German Hungarian Irish Japanese Korean Polish Russian Serbo-Croatian Spanish Ukrainian Portuguese Writing ASL-phabet Hamburg Notation System Stokoe notation SignWriting si5s ASLwrite () Language contact Contact sign Initialized sign Mouthing Signed Oral Languages Indian Signing System Manually coded English Manually coded language in South Africa Manually Coded Malay Paget Gorman Sign System Signed Dutch Signed French Signed German Signed Italian Signed Japanese Signed Polish Signed Spanish Signing Exact English Signed Swedish Others Bilingual–bicultural education Manually coded language Media Films (list) Television shows (list) Persons Jabbar Baghtcheban Jeanette Berglind Pär Aron Borg Thomas Braidwood Laurent Clerc Abbé de l'Épée Roger Fouts Valerie Sutton Thomas Gallaudet Abbé Sicard William Stokoe Pierre Pélissier Organisations Association of Visual Language Interpreters of Canada International Center on Deafness and the Arts Theater of Mimicry and Gesture World Association of Sign Language Interpreters Miscellaneous Baby sign language CHCI chimpanzee center (Washoe, Loulis) Open Outcry Legal recognition U.S. Army hand and arm signals Monastic sign languages Tactile signing Protactile Tic-tac ^a Sign-language names reflect the region of origin. Natural sign languages are not related to the spoken language used in the same region. For example, French Sign Language originated in France, but is not related to French. Conversely, ASL and BSL both originated in English-speaking countries but are not related to each other; ASL however is related to French Sign Language. ^b Denotes the number (if known) of languages within the family. No further information is given on these languages. ^c Italics indicate extinct languages.

1. **[^](#cite_ref-20)** ["How Do We Hear? | NIDCD"](https://www.nidcd.nih.gov/health/how-do-we-hear). *www.nidcd.nih.gov*. 2022-03-16. Retrieved 2023-12-11.

1. **[^](#cite_ref-21)** ["Hearing loss and deafness: Normal hearing and impaired hearing"](https://web.archive.org/web/20201102193448/https://www.ncbi.nlm.nih.gov/books/NBK390300/), *InformedHealth.org [Internet]*, Institute for Quality and Efficiency in Health Care (IQWiG), 2017-11-30, archived from [the original](https://www.ncbi.nlm.nih.gov/books/NBK390300/) on November 2, 2020, retrieved 2023-12-11

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Adapted from the Wikipedia article [Sign language in the brain](https://en.wikipedia.org/wiki/Sign_language_in_the_brain) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Sign_language_in_the_brain?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.