Psycholinguistics/Pidgins, Creoles, and Home Sign

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Introduction[edit | edit source]

One of the challenges of studying language acquisition is that it is an internal process that is difficult to observe, especially when most of those who are actively acquiring language are infants and toddlers. To gain insight into the development of language, some researchers take advantage of exceptional situations in which language acquisition does not progress in a conventional way. Some examples of languages whose development is unconventional are pidgins, creoles, and homesign. Pidgins are language systems which develop when communication is needed between groups of people who do not share the same native language system. A pidgin becomes a creole when it becomes a language learned by the children of the next generation (when it has become a native language). Homesign refers to any gesture-based communication system ("signing") which is not a conventional sign language, commonly invented by deaf children who grow up with parents who are not fluent in a conventional sign language. All three of these language systems are alike in that they develop out of a need to communicate, express thought, and interact with other people in situations where there is no linguistic common ground. What does the development of these phenomena reflect about the processes used to acquire language?

Pidgins and Creoles[edit | edit source]

A pidgin is an auxiliary language created between two or more groups of people who do not share a common language, in a circumstance where communication is essential.

A pidgin language becomes a creole when the children of the next generation learn the pidgin as a native language.

For the purposes of this chapter, and because the two phenomena are so closely intertwined, pidgins and creole languages will be a single topic of discussion. In actuality, a pidgin can be considered a stage in the development of a creole language. Pidgins are auxiliary languages which arise when people who speak different languages are brought together in a situation where communication is essential [1] [2]. Such situations have historically occurred at trade-posts or slave plantations, and were especially common during the colonization of new territories between the years 1500 and 1900 [3][2]. In their attempts to learn and use each other’s languages, communities began using a form of language that combined different components of their own native languages. The pidgin was learned by other members of the community and eventually passed on to their children. When the pidgin was learned as a generation’s native language, it became a creole language [1].

Classification[edit | edit source]

Pidgins and creoles are often classified in terms of their superstrate and substrate languages. The superstrate language is the language on which the pidgin or creole is primarily based, and is usually the language of the colonizing people. The substrate language (or languages) represents the language of the native peoples which contribute in some way to the structure or vocabulary of the pidgin or creole [3] [4]. Some examples of creoles and their superstrate and substrate languages are as follows:

Name Superstrate Substrate(s) Example + Translation
Haitian Creole French African Sanble Jan te malad. (It seems that John is sick. [5])
Louisiana Creole French African, Spanish Mo se rantre dan la chop. (I am going into the shop. [6])
Cape Verdean Creole Portuguese Indigenous language Nu ten un anu na prizao. (We spent ten years in prison. [7])
Malaysian Creole Portuguese (vocabulary) Malay (grammar) Francis teng tres prau. (Francis has three boats. [8])
Hawaiian Creole English Japanese, Filipino, Portuguese, Chinese, native Hawaiian A gon meik ten dala wan aua. (I’m going to make ten dollars an hour. [9].)

Interestingly, creoles around the world share common features. Creole languages tend have a lack of verbal conjugations, generally place the auxiliary verb before the main verb, and have a subject-verb-object structure [3]. This suggests that the development of creoles is driven by some internal mechanism which is shared by humans as species, regardless of specific language or culture. This possibilty will be explored in more detail later in this chapter.

Pidgins, Creoles, and Language Acquisition[edit | edit source]

Pidgins and creoles give researchers a rare opportunity to study language in its earliest stages, and to analyze how language develops as it matures. This provides a window of insight through which many researchers have looked for clues as to how humans acquire language. Two main theories of language acquisition (as it relates to pidgins and creoles) have arisen over the last half century:

  1. The relexification hypothesis, most rigorously defended by Claire Lefebvre and colleagues, which (among other postulates) compares the development of a creole language to the acquisition of a second language, and places creole genesis in the hands of adults in the community.
  2. The language bioprogram hypothesis, proposed by Derek Bickerton and colleagues, which uses pidgin and creole development as evidence for the innateness of humans’ ability to acquire language, and places creole genesis in the hands of children in the community.

The Relexification Hypothesis[edit | edit source]

Search for Relexification on Wikipedia.

Relexification can be described simply as lexical replacement: that is, the lexical items in a person’s first language become replaced by items borrowed from another language [10]. In terms of creole genesis, the relexification hypothesis illustrates how superstrate and substrate languages come together to form a new creole language. According to Lefebvre’s theory, the superstrate language is the “lexifier” or the “target” language, and the substrate languages are the first languages of the people in the community where the creole is developing [11] [12]. Relexification occurs when the semantics and syntax of a lexical entry (i.e., word meaning and usage) from a person’s first language are transferred to a new phonetic string (i.e., a word in its phonetic form). The phonology of the superstrate language plus the semantics and syntax from the substrate language make up a new lexical entry in the creole language [11] [12].

According to this hypothesis, relexification occurs for each substrate language in the community where the creole is developing. This means that speakers of one substrate language will have an early creole lexicon that varies slightly from the creole lexicon of others who speak a different substrate language. However, since these early creole lexicons share a common target language, they will share many common features. When early creole speakers start speaking to one another using their own relexified lexicons, they learn parts of other relexified lexicons and start levelling out the differences between them. Once this levelling is complete, the variation in the lexicons used by different speakers is greatly reduced, and the creole is considered to be a stabilized language [12]. The stages in creole genesis according to the relexification/levelling hypothesis are illustrated below.

Some Criticisms of Relexification[edit | edit source]

Lefebvre has come under criticism for using relexification to compare creole genesis to the incomplete acquisition of a second language. According to this view, substrate language speakers are attempting to acquire the superstrate language but fail to do so – more specifically they successfully acquire the superstrate vocabulary but fall short of acquiring superstrate structure [12]. However, as pointed out by Michel DeGraff in his review entitled “Relexification: A Re-evaluation” [13], there is little evidence that second language acquisition includes relexification. In his analysis of the errors made by English speakers learning French, and French speakers learning English, there was no evidence to support a relexification strategy in acquiring the second language; he did not find that English speakers used French vocabulary mapped onto English grammar and semantics, nor vice versa [13]. For a complete, 95-page document of DeGraff's criticisms of relexification, see the references section at the end of this chapter.

Arguably the most major critique of the relexification hypothesis is that it asserts that only adults, with fully developed first language abilities, are able to contribute to the formation of a creole. As we will see in the next section, not all researchers agree with this view, and have presented some compelling evidence for the role children play in the development of creole languages.

The Language Bioprogram Hypothesis[edit | edit source]

Based on his years of researching creole languages, Derek Bickerton has proposed what he terms “the language bioprogram hypothesis” of language acquisition. His hypothesis proposes that all members of the human race are born with an innate bioprogram for language that is capable of functioning even in the absence of consistent language input. He points out that the evolution of pidgins to creoles is similar across various linguistic backgrounds, and that this is unlikely to occur by chance, suggesting a genetically coded program for language specific to humans [1] [2]. For an in-depth explanation of the LBH, see Bickerton’s 1984 paper: “The Language Bioprogram Hypothesis”.

One of Bickerton’s more fascinating lines of evidence in support of his hypothesis comes from case studies in Hawaii. Hawaii is only location left on Earth where there are still surviving pidgin speakers as well as their subsequent generations of creole-speaking children, providing the unique opportunity to simultaneously study both a pidgin and its developed creole. To analyze the changes that occur when a pidgin becomes creolized, Bickerton studied the language produced by people who arrived in Hawaii between 1900 and 1920 (pidgin group), as well as the language spoken by the first generation of creole speakers (creole group). The language spoken by the pidgin group contained barely recognizable syntax, inconsistent strategies for marking tense (and other grammatical structures), and a heavy influence of the native language of the speaker. In contrast, the language produced by the creole group contained consistent grammatical structures and syntax which were absent from the pidgin spoken by the people from whom they received language input [2]. The people in the creole group cannot have learned these language structures from the previous generation of pidgin speakers, lending evidence to the theory that children possess an innate ability to create an ordered language from “noisy” input (i.e., the language bioprogram hypothesis).

Home Sign[edit | edit source]

Deaf children born to hearing parents face a unique challenge when it comes to language acquisition: their parents are not often fluent in conventional sign language, and the children themselves, due to their inability to hear, cannot be exposed to conventional spoken language. When faced with this seemingly impenetrable barrier to language acquisition, many deaf children spontaneously generate a complicated system of gestures which they use to communicate. These gestures go beyond imitation, pantomime, and pointing to approach the level of a full-blown language, commonly referred to as “homesign”. Without any conventional language input, deaf children are able to create their own sign language which is structured both at the level of the sentence and the word (Goldin-Meadow & Mylander, 1998) and often exhibits complex grammar. The study of this phenomenon has led to some illuminating conclusions about the nature of language acquisition.

A homesign is a gesture-based communication system which is created spontaneously by deaf children who have no conventional language input [14]

Classification[edit | edit source]

Researchers in this area have classified homesign gestures into four basic categories: deictic gestures, which make reference by pointing to some feature of the immediate environment; descriptive gestures, which imitate visual objects through pantomime; conventional gestures, which are used and understood by hearing individuals interacting with the homesigner (such as the well-known “thumbs up” meaning “good”); and markers, which are used to modify a string of gestures (such as a head shake to indicate negativity) [15].

Homesign gestures differ from spontaneous gestures produced by hearing individuals in that they are structured and are produced independently of speech. Homesign gestures also differ from conventional sign language gestures in that they are developed over the lifespan of a single person and are used only by those in the homesigner’s immediate social circle. The latter quality also determines that homesign gestures are more iconic than conventional sign language gestures. Iconicity refers to the similarity of a sign’s form to the object or concept it represents; iconic signs are not arbitrary. Naïve, hearing signers tend to generate only iconic signs, while conventional signers rarely, if ever, use iconic signs [15]. As illustrated by Kuschel’s case study of a deaf-mute named Kangobai,a homesigner’s use of iconic signs fall somewhere between these two extremes, most likely because homesign systems are not used extensively by those around them. This means that at times their signs must represent some key visual features of the referent in order to be deciphered by others [16].

Acquiring a Homesign[edit | edit source]

Children have been shown to be highly capable of acquiring sign languages, even in the absence of consistent sign language input. In 2004, Singleton and Newport documented the achievements of Simon, a seven-year-old deaf child whose parents were non-native American Sign Language (ASL) speakers. The parents’ production of ASL was inconsistent and full of morphological errors. Simon’s production of ASL, on the other hand, surpassed his parents’ and was comparable to ASL produced by children whose parents were native ASL speakers. Since Simon’s parents were his only exposure to ASL, his superior performance lends evidence to suggest that children possess an innate ability to acquire an orderly, rule-based language system even when language input is variable or inaccurate [17]

Simon was able to reorganize and systemize irregular language input, but how is language developed without any language input at all, as seems to be the case with homesigns? Homesigns begin as single points and simple gestures, with one gesture form representing a single meaning. Eventually, homesigning children reorganize their gestures so that single components of each gesture (e.g., handshape, motion) represent components of a meaning (e.g., object class, action) [18]. As the children’s language abilities continue to develop, they produce longer strings of gestures and increase the number of prepositions expressed in a single sentence. Homesign grammatical structure tends to follow a patient-action pairing (e.g., signing CAT-PAT to ask permission to pat the cat), and this has been shown to be consistent across languages and cultures [19].

There is some evidence to the theory that home sign systems begin as imitations of gestural signs produced by the child’s parents. Spontaneous gestures are commonly produced by users of spoken language and often indicate individual events [17]. For example, when talking about opening something with scissors, many people tend to move their first two fingers apart and then back together, like the “snip-snip” action of scissors. This is demonstrated in the figure to the left.

Interestingly, this is also the ASL sign for the action of cutting. However, ASL users generalize and recombine this sign with others to represent other concepts involving the use of scissors, such as a haircut, whereas hearing individuals rarely use a scissor-like gesture when talking about a haircut. Similarly, deaf children with non-native ASL parents seem to produce signs similar to gestures used randomly and spontaneously by their parents, but they are able to generalize these gestures to new combinations and uses [18]. Furthermore, a child’s home sign system contains many signs that are not produced in any form by their parents, indicating that imitation of gestures is perhaps the starting point for the development of a home sign system but is not a limiting factor in the formation of novel signs [18] [17]

Case Study: Nicaraguan Sign Language (NSL)[edit | edit source]

In order to further explore what homesigns can reveal about language acquisition, we will review an interesting case of homesign-turned-sign-language in Nicaragua. In the history of Nicaraguan Sign Language (NSL) we will see that homesigns are capable of exhibiting some of the core features of language, namely that they are discrete, multilayered and productive (for an overview of the core features of language, see Jay, 2003). We will also encounter evidence that some aspects of language generation are innate and independent of external input.

Prior to 1970, deaf children and adults in Nicaragua had little opportunity to interact with other deaf individuals. Some deaf children developed their own homesigns, but these systems were different from person to person and provided no common ground for communication. With the construction of a special education school in 1977 and another in 1981, the deaf were brought together as a community for the first time. The schools’ classes were taught in Spanish (without much success), but the students began using a common system of gestures to communicate with one another both in and outside the classroom (this creation of linguistic common ground is a striking parallel to the formation of pidgins). The gestural system soon expanded into an early form of sign language, and was passed on to the new generations of deaf students (much like a pidgin is learned by the next generation and so becomes a Creole). With each generation, the sign language system was refined and reorganized, and is now recognised as the official Nicaraguan Sign Language (NSL). At present day there are more than 800 deaf signers of NSL, and the language continues to develop [20]. To see some great photos from Ann Senghas' work in Nicaragua, visit her Fieldwork page here.

The unique way in which NSL developed has allowed researchers to study the acquisition of language in innovative ways. By studying the NSL produced by three different generations of deaf Nicaraguan students, Ann Senghas and her colleagues have been able to describe the history and development of NSL, as well as postulate some of the factors affecting the acquisition of language. Firstly, the youngest NSL signers are the most fluent: changes in NSL grammar and morphology that occur with each new generation are passed on to future generations but not the previous ones. Secondly, NSL has progressed from a collection of simple gestures to a hierarchical language system with an infinite number of expressions. When Senghas asked first-generation NSL signers to describe complex motion events, such as wobbling down a street, they often represented manner and path simultaneously in their signs, for example by using their first two fingers to make a walking motion while moving the hand away from the body in a swerving pattern (as represented in box A of the figure to the right).

This is similar to hearing Spanish speakers, who often produce co-speech gestures indicating manner and path of a motion simultaneously. However, second- and third-generation NSL signers tended to articulate manner and path separately, for example by making a circular sign to indicate a curved manner, then moving the hand away from the body to indicate a travelling motion (as represented by box B in the figure to the right). The segmentation of motion into discrete components of manner and path introduces a hierarchy that allows for infinite novel expressions, a defining factor of language [20].

These findings challenge the theory that language evolves through cultural transmission, and suggests that at least some aspects of language acquisition are innate. More specifically, it shows a childhood predisposition for the segmentation and subsequent linear sequencing of linguistic information. In the first generation, language was created without exposure to a pre-existing language structure. In the following generations, sequential combinations of components of the language occurred even when the input model was simultaneous and even though it is perfectly possible to use simultaneous signs. The progression of NSL with each new generation suggests an age effect with the ability to break down, analyze, and recombine language, and indeed this agrees with the previously reported pre-adolescent sensitive period for language acquisition [20] [21].

Conclusion[edit | edit source]

The study of pidgins, creoles, and homesign gives researchers insight into the processes behind language acquisition. However, the data obtained from this research is almost purely observational, and is subject to different interpretations (as has been described above). Studies of pidgin and creole development have given rise to the relexification hypothesis for second language acquisition, and the language bioprogram hypothesis which asserts the innateness of language abilities. The study of homesign systems and NSL in particular supports the theory that language acquisition has a critical period, and that some parts of language can be considered innate. This active field of research will likely continue to turn out new and exciting hypotheses about language acquisition for years to come.

Learning Exercises[edit | edit source]

  • The following table contains examples phrases from some of the most common pidgin and creole languages. Also provided are the phrases translated into other conventional languages.

Creole Phrase English French German Spanish Portuguese Afrikaans Italian
Piti, piti, wazo fe nich li. (Haitian) Little by little, the bird builds its nest. Petit à petit, l'oiseau fait son nid. Allmählich baut der Vogel sein Nest. Poco a poco el pájaro hace su nido. Pouco a pouco, o pássaro constrói seu ninho Bietjie vir bietjie, die voël bou sy nes. Poco a poco, l'uccello costruisce il suo nido
Frah wha pawt yuh deh? (Jamaican) Where are you from? D’où viens-tu? Woher kommen Sie? ¿De dónde eres? Onde está você? Waar kom jy vandaan? Da dove vieni?
Konstitisyon se papie, bayonet se fe. (Haitian) The constitution is paper, bayonets are iron. La constitution est le papier, les baïonnettes sont en fer. Die Verfassung ist Papier, Bajonette Eisen. La Constitución es el papel, las bayonetas son el hierro. A Constituição de papel, baionetas são ferro. Die grondwet is papier, bajonette yster. La Costituzione è carta, baionette sono il ferro.
Dis smol swain i bin go fo maket. (Cameroon Pidgin) This little pig went to market. Ce petit cochon est allé au marché. Das kleine Schwein ging auf den Markt. Este cerdito fue al mercado. Este porquinho foi ao mercado. Hierdie klein vark het om te bemark. Questo porcellino è andato al mercato.
Mo pe aste sa banan. (Seychelles Creole) I am buying this banana. Moi, je veux acheter cette banane. Ich möchte diese Bananen kaufen. Quiero comprar este plátano. Eu quero comprar essa banana. Ek wil hierdie piesang te koop. Voglio comprare questo banana.
Ja fruher wir bleiben. (Papua New Guinea pidgin) Yes, we stayed there at first. Oui, nous sommes restés là en premier. Ja, wir blieben dort früher. Sí, nos quedamos allí al principio. Sim, ficamos ali no início. Ja, ons het daar gebly by die eerste. Sì, siamo rimasti lì in primo luogo.
Konmen lé-z'affè? (Louisiana Creole) How are things? Comment vont les affaires? Wie geht es? ¿Cómo van las cosas? Como vão as coisas? Hoe is dit? Come vanno le cose?
Ka fii sindo u sösö a bëtë i waka u sösö. (Saramaccan) It is better to walk and do nothing than sit and do nothing. Il est préférable de marcher et ne rien faire que de s'asseoir et ne rien faire. Es ist besser zu gehen und nichts tun als zu sitzen und nichts tun. Es mejor caminar y no hacer nada de sentarse y no hacer nada. É melhor andar e não fazer nada do que sentar e não fazer nada. Dit is beter om te loop en niks as sit en niks doen nie doen nie. E 'meglio camminare e non fare niente che sedersi e non fare nulla.
  1. For each creole phrase, try to identify the superstrate language and some possible substrate languages. Keep in mind that many pidgins and creoles are verbal languages only, and do not have a consistent written form. Most spellings of the following phrases are based on pronunciation.
  2. Once you have chosen a superstrate language and one or more substrate languages, to the best of your ability, use the relexification hypothesis to map the superstrate vocabulary onto the structure of the substrate language(s).
  3. What parts, if any, of the resulting sentences resemble the creole phrase you started with?
  4. If none of the sentences created through relexification resemble the creole phrase, perhaps reconsider your choice of superstrate and substrate languages
  5. If you are still confident in your original choices, explain why you chose these languages to be superstrate/substrate(s), and why you think relexification did not “work”.

If you are interested in learning more about Hawai'ian pidgin/creole, the resources at Talking Story About Pidgin are extensive. You can watch videos, see photos of pidgin being used in the community, take pidgin grammar tests and more.

  • Follow the hyperlink and watch Birth of a New Sign Language in Nicaragua, a clip from The Mind’s Big Bang episode of the documentary series Evolution. Pay close attention to the signs produced by Maria Noname and by the children in the second half of the clip.
a. For Maria and the boy featured at minute 5:19, try to identify at least one gesture from each homesign gesture category (deictic, descriptive, conventional, marker).
b. Compare the children’s use of NSL to Maria’s homesigning gestures. What makes NSL a full-blown language, while Maria’s homesign system is rudimentary?
c. From a language acquisition point of view, why do you think efforts to teach Nicaraguan children a conventional sign language failed?
d. Explain how this video clip (and the development of NSL in general) provided evidence for the innateness of language as well as highlighted the importance of linguistic input.
a. If you are a non-signer, which sign language makes the most “sense” to you, NSL or ASL? Explain.
b. How would you (as a naïve observer) identify NSL as a “younger” sign language than ASL?
c. If we were to travel 150 years into the future, how might we expect NSL to change as a language?
  • For the actions described in the following sentences, invent a sign to represent each component of the action (manner/path, manner/action) simultaneously, and a set of signs to represent each component of the action separately.
He hopped in a circle.
The pigeon flew up and away.
She copied notes very quickly.
The ball rolled down the hill.
  1. Which method of representation was easiest for you to invent, simultaneous or separate?
  2. Using your "separated" signs, recombine elements of the previous actions to describe the actions in the following sentences.
He hopped down the hill.
The pigeon flew very quickly.
She copied notes in a circle.
The ball rolled up and away.

(Try these out on your friends! Are they able to interpret what you are trying to say? Is it easier for them to understand simultaneous or separated signs?)

  • For the following objects, come up with a representative hand sign. Invent an iconic sign as well as an abstract sign.
  1. Was it easier to come up with iconic or abstract signs? Why do you think this is?
  2. Ask some friends to interpret your abstract and iconic signs. Why is iconicity important when signing to another person?
  3. Based on the information presented in this chapter, and your answers to the previous two questions, why do you think there is a shift in homesign systems from iconic signs to abstract signs as the homesign develops?
  4. Comment on the pros and cons of using iconic signs.

References[edit | edit source]

  1. 1.0 1.1 1.2 Anderson, R. & Shirai, Y. (1996) Chapter 16: The primacy of aspect in first and second language acquisition: the pidgin-creole connection. In Handbook of Second Language Acquisition, Academic Press Inc.: 527-571.
  2. 2.0 2.1 2.2 2.3 Bickerton, D. (1984) The language bioprogram hypothesis. The Behavioural and Brain Sciences 7: 173-221.

  3. 3.0 3.1 3.2 Monroy, Emily. (2005) What is a creole? Via The Multiracial Activist,
  4. Singler, J. (1988) The homogeneity of the substrate as a factor in pidgin/creole genesis. Language 64: 27-51.
  5. Lefebvre, C. (1998) Creole genesis and the acquisition of grammar: the case of Haitian creole. Cambridge University Press.
  6. Valdman, A. (1998) Dictionary of Louisiana Creole. Indiana University Press.
  7. Baptista, M. (2002) The Syntax of Cape Verdean Creole: The Sotavento Varieties. John Benjamins Publishing.

  8. Mohideen Bin Mohamad Ali, H. & Mohideen, S. (2008) Survival of the Minority Kristang Language in Malaysia. Language in India :
  9. Bickerton, D. (1977) Highlights of least decreolized samples of Hawaiian creole. From: Creole syntax, vol. 2 of 3 volumes, Change and variation in Hawaiian English. Honolulu: University of Hawaii Social Sciences and Linguistics Institute.
  10. Voorhoeve, J. (1973) Historical and linguistic evidence in favour of the relexification theory in the formation of creoles. Language in Society. 2: 133-145.
  11. 11.0 11.1 Lefebvre, C. (1996) The tense, mood and aspect system of Haitian creole and the problem of transmission of grammar in creole genesis. Journal of Pidgin and Creole Languages. 11:231-313.
  12. 12.0 12.1 12.2 12.3 Lefebvre, C. (2001). The interplay of relexification and levelling in creole genesis and development. Linguistics. 39: 371-408.
  13. 13.0 13.1 DeGraff, M. (2002). Relexification: A Re-evaluation. Anthropological Linguistics.4: 321-414
  14. Torigoe, T. & Takei, W. (2002) A descriptive analysis of pointing and oral movements in a home sign system. Sign Language Studies 2: 281-295.
  15. 15.0 15.1 Morford, J. (1996) Insights to language from the study of gesture: A review of research on the gestural communication of non-signing deaf people. Language and Communication 16: 165-78.
  16. Kuschel, R. (1973) The silent inventor: The creation of a sign-language by the only deaf-mute on a Polynesian island. Sign Language Studies 3: 1-27.
  17. 17.0 17.1 17.2 Singleton, J. & Newport, E. (2004) When learners surpass their models: The acquisition of American Sign Language from inconsistent input. Cognitive Psychology 49: 370-407.
  18. 18.0 18.1 18.2 Goldin-Meadow, S. & Mylander, C. (1990) Beyond the input given: The child’s role in the acquisition of language. Language 66: 323-355.
  19. Goldin-Meadow, S., Ozyurek, A., Sancar, B. & Mylander, C. (2008) Chapter 2: Making language around the globe - A crosslinguistic study of homesign in the United States, China, and Turkey. In Crosslinguistic Approaches to the Study of Language: 27-39.

  20. 20.0 20.1 20.2 Senghas, A., Kita, S. & Ozyurek, A. (2004) Children creating core properties of language: Evidence from an emerging sign language in Nicaragua. Science 305: 1779-1782
  21. Siegal, M. (2004) Signposts to the essence of language. Science 305: 1720-1721.