|This article needs additional citations for verification. (December 2013)|
|Applied and experimental|
Language development is a process starting early in human life. Infants start without language, yet by 4 months of age, babies can discriminate speech sounds and engage in babbling. Some research has shown that the earliest learning begins in utero when the fetus starts to recognize the sounds and speech patterns of its mother's voice.
Usually, productive language is considered to begin with a stage of preverbal communication in which infants use gestures and vocalizations to make their intents known to others. According to a general principle of development, new forms then take over old functions, so that children learn words to express the same communicative functions which they had already expressed by preverbal means.
- 1 Theoretical frameworks of language development
- 2 Biological preconditions
- 3 Gender Differences
- 4 Environmental Influences
- 5 Social preconditions
- 6 Language Disorders
- 7 See also
- 8 Reference list
- 9 Further reading
- 10 External links
Theoretical frameworks of language development
Language development is thought to proceed by ordinary processes of learning in which children acquire the forms, meanings and uses of words and utterances from the linguistic input. The method in which we develop language skills is universal however, the major debate is how the rules of syntax are acquired. There are two major approaches to syntactic development, an empiricist account by which children learn all syntactic rules from the linguistic input, and a nativist approach by which some principles of syntax are innate and are transmitted through the human genome.
The nativist theory, proposed by Noam Chomsky, argues that language is a unique human accomplishment. Chomsky says that all children have what is called an innate language acquisition device (LAD). Theoretically, the LAD is an area of the brain that has a set of universal syntactic rules for all languages. This device provides children with the ability to construct novel sentences using learned vocabulary. Chomsky's claim is based upon the view that what children hear - their linguistic input - is insufficient to explain how they come to learn language. He argues that linguistic input from the environment is limited and full of errors. Therefore, nativists assume that it is impossible for children to learn linguistic information solely from their environment. However, because children possess this LAD, they are in fact, able to learn language despite incomplete information from their environment. This view has dominated linguistic theory for over fifty years and remains highly influential, as witnessed by the number of articles in journals and books.
The empiricist theory suggests, contra Chomsky, that there is enough information in the linguistic input children receive and therefore, there is no need to assume an innate language acquisition device exists (see above). Rather than a LAD which evolved specifically for language, empiricists believe that general brain processes are sufficient enough for language acquisition. During this process, it is necessary for the child to be actively engaged with their environment. In order for a child to learn language, the parent or caregiver adopts a particular way of appropriately communicating with the child; this is known as child-directed speech (CDS). CDS is used so that children are given the necessary linguistic information needed for their language. Empiricism is a general approach and sometimes goes along with the interactionist approach. Statistical language acquisition, which falls under empiricist theory, suggests that infants acquire language by means of pattern perception.
Other researchers embrace an interactionist perspective, consisting of social-interactionist theories of language development. In such approaches, children learn language in the interactive and communicative context, learning language forms for meaningful moves of communication. These theories focus mainly on the caregiver's attitudes and attentiveness to their children in order to promote productive language habits.
An older empiricist theory, the behaviorist theory proposed by B. F. Skinner suggested that language is learned through operant conditioning, namely, by imitation of stimuli and by reinforcement of correct responses. This perspective has not been widely accepted at any time, but by some accounts, is experiencing a resurgence. New studies use this theory now to treat individuals diagnosed with autism spectrum disorders. Additionally, Relational Frame Theory is growing from the behaviorist theory which is important for Acceptance and Commitment Therapy.  Some empiricist theory accounts today use behaviorist models.
Other relevant theories about language development include Piaget's theory of cognitive development, which considers the development of language as a continuation of general cognitive development and Vygotsky's social theories that attribute the development of language to an individual's social interactions and growth.
Evolutionary biologists are skeptical of the claim that syntactic knowledge is transmitted in the human genome. However, many researchers claim that the ability to acquire such a complicated system is unique to the human species. Non-biologists also tend to believe that our ability to learn spoken language may have been developed through the evolutionary process and that the foundation for language may be passed down genetically. The ability to speak and understand human language requires speech production skills and abilities as well as multisensory integration of sensory processing abilities.
One hotly debated issue is whether the biological contribution includes capacities specific to language acquisition, often referred to as universal grammar. For fifty years, linguist Noam Chomsky has argued for the hypothesis that children have innate, language-specific abilities that facilitate and constrain language learning. In particular, he has proposed that humans are biologically prewired to learn language at a certain time and in a certain way, arguing that children are born with a Language Acquisition Device (LAD). However, since he developed the Minimalist Program, his latest version of theory of syntactic structure, Chomsky has reduced the elements of universal grammar which are in his opinion to be prewired in humans to just the principle of recursion, thus voiding most of the nativist endeavor.
Researchers who believe that grammar is learned rather than innate, have hypothesized that language learning results from general cognitive abilities and the interaction between learners and their human interactants. It has also recently been suggested that the relatively slow development of the prefrontal cortex in humans may be one reason that humans are able to learn language, whereas other species are not. Further research has indicated the influence of the FOXP2 gene.
Children versus adults
It seems as if during the early years of language development females exhibit an advantage over males of the same age. When infants between the age of 16 to 22 months were observed interacting with their mothers, a female advantage was obvious. The females in this age range showed more spontaneous speech production than the males and this finding was not due to mothers speaking more with daughters than sons. In addition, boys between 2 and 6 years as a group did not show higher performance in language development over their girl counterparts on experimental assessments. In studies using adult populations, 18 and over, it seems that the female advantage may be task dependent. Depending on the task provided, a female advantage may or may not be present.
Lateralization effect on language
It is currently believed that in regards to brain lateralization males are left lateralized, while females are bilateralized. Studies on patients with unilateral lesions have provided evidence that females are in fact more bilateralized with their verbal abilities. It seems that when a female has experienced a lesion to the left hemisphere she is better able to compensate for this damage than a male can. If a male has a lesion in the left hemisphere his verbal abilities are greatly impaired in comparison to a control male of the same age without that damage. However, these results may also be task dependent as well as time dependent.
The environment a child develops in has influences on language development. The environment provides language input for the child to process. Speech by adults to children help provide the child with correct language usage repetitively. Environmental influences on language development are explored in the tradition of social interactionist theory by such researchers as Jerome Bruner, Alison Gopnik, Andrew Meltzoff, Anat Ninio, Roy Pea, Catherine Snow, Ernest Moerk and Michael Tomasello. Jerome Bruner who laid the foundations of this approach in the 1970s, emphasized that adult "scaffolding" of the child's attempts to master linguistic communication is an important factor in the developmental process.
One component of the young child's linguistic environment is child-directed speech (also known as baby talk or motherese), which is language spoken in a higher pitch than normal with simple words and sentences. Although the importance of its role in developing language has been debated, many linguists think that it may aid in capturing the infant's attention and maintaining communication. When children begin to communicate with adults, this motherese speech allows the child the ability to discern the patterns in language and to experiment with language.
Throughout research done, it is concluded that children exposed to extensive vocabulary and complex grammatical structures more quickly develop language and also have a more accurate syntax than children raised in environments without complex grammar exposed to them. With motherese, the mother talks to the child and responds back to the child, whether it be a babble the child made or a short sentence. While doing this, the adult is prompting the child to continue communicating which may help a child develop language sooner than children raised in environments where communication is not fostered.
Child-directed speech will concentrate on small core vocabulary, here and now topics, exaggerated facial expressions and gestures, frequent questioning, paralinguistic changes, and verbal rituals. An infant is least likely to produce vocalizations when changed, fed, or rocked. The infant will more likely produce vocalizations when a nonverbal behavior such as touching or smiling is directed at the infant.
Child-directed speech will also catch the child's attention and in situations where words for new objects are being expressed to the child this form of speech may help the child recognize the speech cues and the new information provided. Data shows that children raised in highly verbal families had higher language scores than those children raised in low verbal families. Continuously hearing complicated sentences throughout language development increases the child's ability to understand these sentences and then to use complicated sentences as they develop. Studies have shown that students enrolled in high language classrooms have two times the growth in complex sentences usage than students in classrooms where teachers do not frequently use complex sentences.
Adults use strategies other than child-directed speech like recasting, expanding, and labeling: Recasting is rephrasing something the child has said, perhaps turning it into a question or restating the child's immature utterance in the form of a fully grammatical sentence. For example, a child saying "cookie now" a parent may respond with "Would you like a cookie now?" Expanding is restating, in a linguistically sophisticated form, what a child has said. For example, a child may say "car move road" and the parent may respond "A car drives on the road." Labeling is identifying the names of objects If a child points to an object such as a couch the mother may say "couch" in response. Labeling can also be characterized as referencing.
Some language development experts have characterized child directed speech in stages. Primarily, the parents will use repetition and also variation to maintain the infant's attention. Secondly, the parent will simplify speech to help in language learning. Third, any modifications in speech will maintain the responsiveness of the child. These modifications develop into a conversation that provides context for the development.
Cultural and Socioeconomic Effects on Language Development
While most children throughout the world develop language at similar rates and without difficulty, cultural and socioeconomic differences have been shown to influence development. An example of cultural differences in language development can be seen when comparing the interactions of mothers in the United States with their infants with mothers in Japan. Mothers in the United States use more questions, are more information oriented, and use more grammatically correct utterances with their 3-month-olds. Mothers in Japan, on the other hand, use more physical contact with their infants, and more emotion-oriented, nonsense, and environmental sounds, as well as baby talk, with their infants. These differences in interaction techniques reflect differences in "each society's assumptions about infants and adult-to adult cultural styles of talking."
Specifically in North American culture, maternal race, education, and socioeconomic class influence parent-child interactions in the early linguistic environment. When speaking to their infants, mothers from middle class "incorporate language goals more frequently in their play with their infants," and in turn, their infants produce twice as many vocalizations as lower class infants. Mothers from higher social classes who are better educated also tend to be more verbal, and have more time to spend engaging with their infants in language. Additionally, lower class infants may receive more language input from their siblings and peers than from their mothers.
It is crucial that children are allowed to socially interact with other people who can vocalize and respond to questions. For language acquisition to develop successfully, children must be in an environment that allows them to communicate socially in that language.
There are a few different theories as to why and how children develop language. The most popular—and yet heavily debated—explanation is that language is acquired through imitation. The two most accepted theories in language development are psychological and functional. Psychological explanations focus on the mental processes involved in childhood language learning. Functional explanations look at the social processes involved in learning the first language.
There are four main components of language:
- Phonology involves the rules about the structure and sequence of speech sounds.
- Semantics consists of vocabulary and how concepts are expressed through words.
- Grammar involves two parts.
- Pragmatics involves the rules for appropriate and effective communication. Pragmatics involves three skills:
- using language for greeting, demanding etc.
- changing language for talking differently depending on who it is you are talking to
- following rules such as turn taking, staying on topic
Each component has its own appropriate developmental periods.
From shortly after birth to around one year, the baby starts to make speech sounds. At around two months, the baby will engage in cooing, which mostly consists of vowel sounds. At around four months, cooing turns into babbling which is the repetitive consonant-vowel combinations. Babies understand more than they are able to say. In this 0-8 months range, the child is engaged in vocal play of vegetative sounds, laughing, and cooing.
Once the child hits the 8-12 month range the child engages in canonical babbling ie. dada as well as variegated babbling. This jargon babbling with intonational contours the language being learned.
From 12-24 months, babies can recognize the correct pronunciation of familiar words. Babies will also use phonological strategies to simplify word pronunciation. Some strategies include repeating the first consonant-vowel in a multisyllable word ('TV'--> 'didi') or deleting unstressed syllables in a multisyllable word ('banana'-->'nana'). Within this first year, two word utterances and two syllable words emerge. This period is often called the holophrastic stage of development, because one word conveys as much meaning as an entire phrase. For instance, the simple word "milk" can imply that the child is requesting milk, noting spilled milk, sees a cat drinking milk, etc.
By 24-30 months awareness of rhyme emerges as well as rising intonation.
By 36-60 months, phonological awareness continues to improve as well as pronunciation.
By 6–10 years, children can master syllable stress patterns which helps distinguish slight differences between similar words.
From birth to one year, comprehension (the language we understand) develops before production (the language we use). There is about a 5 month lag in between the two. Babies have an innate preference to listen to their mother's voice. Babies can recognize familiar words and use preverbal gestures.
Within the first '12-18 months semantic roles are expressed in one word speech including agent, object, location, possession, nonexistence and denial. Words are understood outside of routine games but the child still needs contextual support for lexical comprehension.
18-24 months Prevalent relations are expressed such as agent-action, agent-object, action-location Also, there is a vocabulary spurt between 18–24 months, which includes fast mapping. Fast mapping is the babies' ability to learn a lot of new things quickly. The majority of the babies' new vocabulary consists of object words (nouns) and action words (verbs).
30-36 months The child is able to use and understand why question and basic spatial terms such as in, on or under.
36-42 months There is an understanding of basic color words and kinship terms. Also, the child has an understanding of the semantic relationship between adjacent and conjoined sentences, including casual and contrastive.
42-48 months When and how questions are comprehended as well as basic shape words such as circle, square and triangle.
48-60 months Knowledge of letter names and sounds emerges, as well as numbers.
By 3–5 years, children usually have difficulty using words correctly. Children experience many problems such as underextensions, taking a general word and applying it specifically (for example, 'blankie') and overextensions, taking a specific word and applying it too generally (example, 'car' for 'van'). However, children coin words to fill in for words not yet learned (for example, someone is a cooker rather than a chef because a child will not know what a chef is). Children can also understand metaphors.
From 6–10 years, children can understand meanings of words based on their definitions. They also are able to appreciate the multiple meanings of words and use words precisely through metaphors and puns. Fast mapping continues. Within these years, children are now able to acquire new information from written texts and can explain relationships between multiple meaning words. Common idioms are also understood.
From 1–2 years, children start using telegraphic speech, which are two word combinations, for example 'wet diaper'. Brown (1973) observed that 75% of children's two-word utterances could be summarised in the existence of 11 semantic relations:
Eleven important early semantic relations and examples based on Brown 1973
At around 3 years, children engage in simple sentences, which are 3 word sentences. Simple sentences follow adult rules and get refined gradually. Grammatical morphemes get added as these simple sentences start to emerge.
By 3–5 years, children continue to add grammatical morphemes and gradually produce complex grammatical structures.
By 6–10 years, children refine the complex grammatical structures such as passive voice.
- By 1–2 years, they can engage in conversational turn taking and topic maintenance.
- By ages 3–5, children can master illocutionary intent, knowing what you meant to say even though you might not have said it and turnabout, which is turning the conversation over to another person.
- By age 6-10, shading occurs, which is changing the conversation topic gradually. Children are able to communicate effectively in demanding settings, such as on the telephone.
The Consequences of Bilingualism on Language Development
There is a large debate regarding whether or not bilingualism is truly beneficial to children. Parents of children often view learning a second language throughout elementary and high school education beneficial to the child. Another perspective dictates that the second language will just confuse the child and prevent them from mastering their primary language. Studies have shown that American bilingual children have greater cognitive flexibility, better perceptual skills and tend to be divergent thinkers than monolingual children between the ages of five to ten. However, studies comparing Swedish-Finnish bilingual children and Swedish monolingual children between the ages of five to seven have also shown that the bilingual children have a smaller vocabulary than monolingual children. In another study throughout America, elementary school English-monolingual children performed better in mathematics and reading activities than their non-English-dominant bilingual and non-English monolingual peers from kindergarten to grade five. Learning two languages simultaneously can be beneficial or a hindrance to a child’s language and intellectual development. Further research is necessary to continue to shed light on this debate.
A language disorder is the impaired comprehension and or use of a spoken, written, and/or other symbol system. A disorder may involve problems in the following areas:
- The form of language ie. phonology, morphology, or syntax
- The content i.e. semantics
- The function of language in communication ie. pragmatics
Olswang and colleagues have identified a series of behaviors in children in the 18-36 month range that are predictors for the need of language intervention.
These predictors include:
- A smaller than average vocabulary
- A language comprehension delay of 6 months or a comprehension deficit with a large comprehension production gap
- Phonological problems such as restricted babbling or limited vocalizations
- Few spontaneous vocal imitations and reliance on direct modeling in imitation tasks
- Little combinatorial or symbolic play
- Few communicative or symbolic gestures
- Behavior problems
Language disorders and conditions which can cause language development problems are many including:
- Kennison, Shelia M. (2013-07-30). Introduction to language development. Los Angeles: SAGE Publications. ISBN 978-1-4129-9606-8. OCLC 830837502.
- Poll, G. H. (2011). "Increasing the Odds: Applying Emergentist Theory in Language Intervention". Language, Speech, and Hearing Services in Schools 42 (4): 580–591. doi:10.1044/0161-1461(2011/10-0041). PMC 3164388. PMID 21616988.
- Roediger, R. (2004) "What happened to Behaviorism." American Psychological Society.
- Ramscar M, Yarlett D (November 2007). "Linguistic self-correction in the absence of feedback: a new approach to the logical problem of language acquisition". Cogn Sci 31 (6): 927–60. doi:10.1080/03640210701703576. PMID 21635323.
- Clibbens, John (October 1993). "From theory to practice in child language development". Down Syndrome Research and Practice 1 (3): 101–106. Retrieved 2012-11-20.
- Schneider, Phyllis; Watkins, Ruth (April 1996). "Applying Vygotskian Developmental Theory to Language Intervention". Language, Speech & Hearing Services in Schools 27 (2): 157–170.
- Santrock, John W. (2007). A Topical Approach to Lifespan Development. McGraw-Hill Humanities/Social Sciences/Languages. ISBN 0-07-338264-7. OCLC 171151508.
- Hauser MD, Chomsky N, Fitch WT (November 2002). "The faculty of language: what is it, who has it, and how did it evolve?". Science 298 (5598): 1569–79. doi:10.1126/science.298.5598.1569. PMID 12446899.
- Thompson-Schill SL, Ramscar M, Chrysikou EG (2009). "Cognition without control: When a little frontal lobe goes a long way". Curr Dir Psychol Sci 18 (5): 259–263. doi:10.1111/j.1467-8721.2009.01648.x. PMC 2855545. PMID 20401341.
- Ramscar M, Gitcho N (July 2007). "Developmental change and the nature of learning in childhood". Trends Cogn. Sci. (Regul. Ed.) 11 (7): 274–9. doi:10.1016/j.tics.2007.05.007. PMID 17560161.
- Scharff C, Petri J (July 2011). "Evo-devo, deep homology and FoxP2: implications for the evolution of speech and language". Philos. Trans. R. Soc. Lond., B, Biol. Sci. 366 (1574): 2124–40. doi:10.1098/rstb.2011.0001. PMC 3130369. PMID 21690130.
- Huttenlocher J., Haight W., Bryk A., Seltzer M., Lyons T. (1991). "Early vocabulary growth: Relation to language input and gender". Developmental Psychology 27 (2): 236–248.
- Bornstein, M. H. (2004). "Specific and general language performance across early childhood: Stability and gender considerations". First Language 24 (3): 267–304. doi:10.1177/0142723704045681.
- Frith, Uta; Vargha-Khadem, Faraneh (2001). "Are there sex differences in the brain basis of literacy related skills? Evidence from reading and spelling impairments after early unilateral brain damage". Neuropsychologia 39 (13): 1485–1488. doi:10.1016/S0028-3932(01)00063-X.
- Kansaku, Kenji; Kitazawa, Shigeru (2001). "Imaging studies on sex differences in the lateralization of language". Neuroscience Research 41 (4): 333–337. doi:10.1016/S0168-0102(01)00292-9.
- Mani, Nivedita; Plunkett, Kim (2010). "Twelve-Month-Olds Know Their Cups From Their Keps and Tups". Infancy 15 (5): 445–470. doi:10.1111/j.1532-7078.2009.00027.x. ISSN 1525-0008.
- Owens, Robert E. (2012). Language development : an introduction. Boston: Pearson. pp. 130–135. ISBN 978-0-13-258252-0. OCLC 682896734.
- Fernandez, Eva (2011). Fundamentals of Psycholinguistics. West Sussex: Wiley-Blackwell. p. 110.
- Brandone, Amanda C; Salkind, Sara J.; Golinkoff, Roberta Michnick; Hirsh-Pasek, Kathy (2006). "Language Development". In George G Bear; Kathleen M Minke. Children's needs III : development, prevention, and intervention (Bethesda, Md: National Association of School Psychologists). ISBN 9780932955791. OCLC 70691810. Retrieved 2013-12-09.
- Brown, R. (1973). A first language: The early stages. Harvard University Press.
- Bialystok, E.; Craik, FI.; Luk, G. (Apr 2012). "Bilingualism: consequences for mind and brain.". Trends Cogn Sci 16 (4): 240–50. doi:10.1016/j.tics.2012.03.001. PMC 3322418. PMID 22464592.
- Blumenfeld, H; Faroqi-Shah, Y (2009). "Bilingualism: Consequences for language, cognition, development, and the brain". American Speech-Language-Hearing Association 14 (13): 10.
- Blumenfeld, H; Faroqi-Shah, Y (2009). "Bilingualism: Consequences for language, cognition, development, and the brain". American Speech-Language-Hearing Association 14 (13): 10.
- Korkman, M.; Stenroos, M.; Mickos, A.; Westman, M.; Ekholm, P.; Byring, R. (Sep 2012). "Does simultaneous bilingualism aggravate children's specific language problems?". Acta Paediatr 101 (9): 946–52. doi:10.1111/j.1651-2227.2012.02733.x. PMID 22591054.
- Han, WJ. (2012). "Bilingualism and academic achievement.". Child Dev 83 (1): 300–21. doi:10.1111/j.1467-8624.2011.01686.x. PMID 22098584.
- Olswang, Lesley B; Rodriguez, Barbara; Timler, Geralyn (1998). "Recommending Intervention for Toddlers With Specific Language Learning Difficulties" 7. American Journal of Speech-Language Pathology. pp. 23–32. Retrieved 9 December 2013.
- Abbot-Smith, Kirsten; Tomasello, Michael (2006). "Exemplar-learning and schematization in a usage-based account of syntactic acquisition". The Linguistic Review 23 (3): 275–290. doi:10.1515/TLR.2006.011.
- Balari S, Benítez-Burraco A, Camps M, Longa VM, Lorenzo G, Uriagereka J (2011). "The archaeological record speaks: bridging anthropology and linguistics". Int J Evol Biol 2011: 382679. doi:10.4061/2011/382679. PMC 3123707. PMID 21716806.
- Berk, Laura E. (2009). "9, Language Development". Child development. Boston: Pearson Education/Allyn & Bacon. ISBN 0-205-61559-7. OCLC 637146042.
- Bornstein, MH.; Putnick, DL. (Mar 2012). "Stability of language in childhood: a multiage, multidomain, multimeasure, and multisource study.". Dev Psychol 48 (2): 477–91. doi:10.1037/a0025889. PMC 3412562. PMID 22004343.
- Campbell R (March 2008). "The processing of audio-visual speech: empirical and neural bases". Philosophical Transactions of the Royal Society B 363 (1493): 1001–10. doi:10.1098/rstb.2007.2155. PMC 2606792. PMID 17827105.
- Chomsk, Noam (1963-65). "Three models for the description of language". In Robert Duncan Luce,. Readings in mathematical psychology. (New York: Wiley). OCLC 190574.
- Chomsky, Noam (1965). Aspects of the theory of syntax. Cambridge: M.I.T. Press. ISBN 9780262530071. OCLC 309976.
- Hickok G, Poeppel D (2004). "Dorsal and ventral streams: a framework for understanding aspects of the functional anatomy of language". Cognition 92 (1-2): 67–99. doi:10.1016/j.cognition.2003.10.011. PMID 15037127.
- Kuhl PK, Conboy BT, Coffey-Corina S, Padden D, Rivera-Gaxiola M, Nelson T (March 2008). "Phonetic learning as a pathway to language: new data and native language magnet theory expanded (NLM-e)". Philosophical Transactions of the Royal Society B 363 (1493): 979–1000. doi:10.1098/rstb.2007.2154. PMC 2606791. PMID 17846016.
- Perani D, Saccuman MC, Scifo P, et al. (September 2011). "Neural language networks at birth". Proc. Natl. Acad. Sci. U.S.A. 108 (38): 16056–61. doi:10.1073/pnas.1102991108. PMC 3179044. PMID 21896765.
- Richardson FM, Price CJ (October 2009). "Structural MRI studies of language function in the undamaged brain". Brain Struct Funct 213 (6): 511–23. doi:10.1007/s00429-009-0211-y. PMC 2749930. PMID 19618210.
- Rowe, ML.; Ozçalişkan, S.; Goldin-Meadow, S. (Jan 2008). "Learning words by hand: Gesture's role in predicting vocabulary development.". First Lang 28 (2): 182–199. doi:10.1177/0142723707088310. PMC 2745165. PMID 19763249.
- Wandell BA, Rauschecker AM, Yeatman JD (January 2012). "Learning to see words". Annu Rev Psychol 63: 31–53. doi:10.1146/annurev-psych-120710-100434. PMC 3228885. PMID 21801018.
|Library resources about