Language acquisition is the process by which humans acquire
the capacity to perceive and comprehend language, as well as to produce
and use words
and
sentences to communicate. Language acquisition is one of the
quintessential human traits, because nonhumans do not communicate by
using language.[1]
Language acquisition usually refers to first-language acquisition,
which studies infants' acquisition of their native language. This is
distinguished from
second-language acquisition, which deals with the acquisition
(in both children and adults) of additional languages.
The capacity to successfully use language requires one to acquire a
range of tools including
phonology,
morphology,
syntax,
semantics, and an extensive
vocabulary. Language might be vocalized as speech or manual as in
sign. The human language capacity is represented in the brain. Even
though the human language capacity is finite, one can say and understand
an infinite number of sentences, which is based on a syntactic principle
called
Recursion. Evidence suggests that every individual has three
recursive mechanisms that allow sentences to go indeterminately. These
three mechanisms are: relativization, complementation and
coordination.
The capacity to acquire and use language is a key aspect that
distinguishes humans from other beings. Although it is difficult to pin
down what aspects of language are uniquely human, there are a few design
features that can be found in all known forms of human language, but
that are missing from forms of
animal communication. For example, many animals are able to
communicate with each other by signaling to the things around them, but
this kind of communication lacks the arbitrariness of human vernaculars
(in that there is nothing about the sound of the word "dog" that would
hint at its meaning). Other forms of animal communication may utilize
arbitrary sounds, but are unable to combine those sounds in different
ways to create completely novel messages that can then be automatically
understood by another.
Hockett called this design feature of human language "productivity".
It is crucial to the understanding of human language acquisition that we
are not limited to a finite set of words, but, rather, must be able to
understand and utilize a complex system that allows for an infinite
number of possible messages. So, while many forms of animal
communication exist, they differ from human languages, in that they have
a limited range of non-syntactically structured vocabulary tokens that
lack cross cultural variation between groups.[3]
A major debate in understanding language acquisition is how these
capacities are picked up by
infants
from the linguistic input. Input in the linguistic
context is defined as "All words, contexts, and other forms of
language to which a learner is exposed, relative to acquired proficiency
in first or
second languages".
Nativists find it difficult to believe, considering the hugely
complex nature of human languages, and the relatively limited
cognitive abilities of an infant, that infants are able to acquire
most aspects of language without being explicitly taught. Children,
within a few years of birth, understand the
grammatical rules of their native language without being explicitly
taught, as one learns grammar in school.[4]
A range of theories of language acquisition have been proposed in order
to explain this apparent problem. These theories, championed by the
likes of
Noam Chomsky and others, include
innatism and
Psychological nativism, in which a child is born prepared in some
manner with these capacities, as opposed to other theories in which
language is simply learned as other cognitive skills, including such
mundane motor skills as learning to ride a bike. The conflict between
the theories assuming humans are born with syntactic knowledge and those
that claim all such knowledge is the product of learning from one's
environment is often referred to as the "Nature
vs. Nurture" debate. Some think that there are some qualities of
language acquisition that the human brain is automatically wired for (a
"nature" component) and some that are shaped by the particular language
environment in which a person is raised (a "nurture" component). Others,
especially evolutionary biologists, strongly object to assuming
syntactic knowledge is genetically encoded and provided by automatic
wiring of the brain.
History
Philosophers in ancient societies were interested in how humans
acquired the ability to understand and produce language well before
empirical methods for testing those theories were developed, but for
the most part they seemed to regard language acquisition as a subset of
man's ability to acquire knowledge and learn concepts.[5]
Some early, observation based ideas about language acquisition were
proposed by
Plato, who felt that word-meaning mapping in some form was innate.
Additionally,
Sanskrit grammarians debated for over twelve centuries whether
humans' ability to recognize the meaning of words was god-given
(possibly innate) or passed down by previous generations and learned
from already established conventions—e.g. a child learning the word for
cow by listening to trusted speakers talking about cows.[6]
In a more modern context, empiricists, like
Hobbes and
Locke, argued that knowledge (and, for Locke, language) emerge
ultimately from abstracted sense impressions. These arguments lean
towards the "nurture" side of the argument- that language is acquired
through sensory experience. This led to
Carnap's Aufbau, an attempt to learn all knowledge from sense datum,
using the notion of "remembered as similar" to bind these into clusters,
which would eventually map into language.[7]
Proponents of
Behaviorism argued that language may be learned through a form of
operant conditioning. In
B. F. Skinner's
Verbal Behaviour (1957), he suggested that the successful use of
a sign, such as a word or
lexical unit, given a certain stimulus,
reinforces its "momentary" or contextual probability. Since
operant conditioning is contingent on reinforcement by rewards, a
child would learn that a specific combination of sounds stands for a
specific thing through repeated successful associations made between the
two. A "successful" use of a sign would be one in which the child is
understood (for example, a child saying "up" when he or she wants to be
picked up) and rewarded with the desired response from another person,
thereby reinforcing the child's understanding of the meaning of that
word and making it more likely that he or she will use that word in a
similar situation in the future. Some
Empiricist theories of language acquisition include the
statistical learning theory Charles F. Hockett of language
acquisition,
Relational Frame Theory,
functionalist linguistics,
social interactionist theory, and usage-based language acquisition.
Skinner's behaviourist idea was strongly attacked by
Noam Chomsky in a review article in 1959, calling it "largely
mythology" and a "serious delusion".[8]
Chomsky believed Skinner failed to account for the central role of
syntactic knowledge in language competence. Chomsky also rejected the
term "learning," which Skinner used to claim that children "learn"
language through operant conditioning.[9]
Instead, Chomsky argued for a mathematical approach to language
acquisition, based on a study of
syntax.
General approaches
Social
interactionism
Social interactionist theory is an explanation of language
development emphasizing the role of social interaction between the
developing child and linguistically knowledgeable adults. It is based
largely on the socio-cultural theories of Soviet psychologist
Lev Vygotsky, and made prominent in the Western world by
Jerome Bruner.[10]
Unlike other approaches, it emphasizes the role of feedback and
reinforcement in language acquisition. Specifically, it asserts that
much of a child's linguistic growth stems from modeling of and
interaction with parents and other adults, who very frequently provide
instructive correction.[11]
It is thus somewhat similar to
behaviorist accounts of language, though it differs substantially in
that it posits the existence of a social-cognitive model and other
mental structures within children (a sharp contrast to the "black
box" approach of classical behaviorism).
Another key idea within the theory of social interactionism is that
of the
zone of proximal development. Briefly, this is a theoretical
construct denoting the set of tasks a child is capable of performing
with guidance, but not alone.[12]
As applied to language, it describes the set of linguistic tasks (proper
syntax, suitable vocabulary usage, etc.) a child cannot carry out on
their own at a given time, but can learn to carry out if assisted by an
able adult.
Relational
frame theory
The
relational frame theory (RFT) (Hayes, Barnes-Holmes, Roche, 2001),
provides a wholly selectionist/learning account of the origin and
development of language competence and complexity. Based upon the
principles of
Skinnerian
behaviorism, RFT posits that children acquire language purely
through interacting with the environment. RFT theorists introduced the
concept of
functional contextualism in language learning, which emphasizes the
importance of predicting and influencing psychological events, such as
thoughts, feelings, and behaviors, by focusing on manipulable variables
in their context. RFT distinguishes itself from Skinner's work by
identifying and defining a particular type of
operant conditioning known as derived relational responding, a
learning process that, to date, appears to occur only in humans
possessing a capacity for language. Empirical studies supporting the
predictions of RFT suggest that children learn language via a system of
inherent reinforcements, challenging the view that language acquisition
is based upon innate, language-specific cognitive capacities.[13]
Emergentism
Emergentist theories, such as
MacWhinney's
competition model, posit that language acquisition is a
cognitive process that emerges from the interaction of biological
pressures and the environment. According to these theories, neither
nature nor nurture alone is sufficient to trigger language learning;
both of these influences must work together in order to allow children
to acquire a language. The proponents of these theories argue that
general cognitive processes subserve language acquisition and that the
end result of these processes is language-specific phenomena, such as
word learning and
grammar
acquisition. The findings of many empirical studies support the
predictions of these theories, suggesting that language acquisition is a
more complex process than many believe.[14]
Syntax and
morphology
As
syntax began to be studied more closely in the early 20th century,
in relation to language learning, it became apparent to linguists,
psychologists, and philosophers that knowing a language was not merely a
matter of associating words with concepts, but that a critical aspect of
language involves knowledge of how to put words together—sentences are
usually needed in order to communicate successfully, not just isolated
words.[5]
When acquiring a language, it is often found that most verbs, such as
those in the English language, are
irregular verbs. These verbs do not follow specific rules to form
the past tense. Young children learn the past tense of verbs
individually; however, when they are taught a "rule", such as adding -ed
to form the past tense, they begin to exhibit overgeneralization errors
(e.g. "runned", "hitted") as a result of learning these basic
syntactical rules that do not apply to all verbs. The children then need
to relearn how to apply these past tense rules to the irregular verbs
they had previously done correctly.[15]
Generativism
Generative grammar, associated especially with the work of
Noam Chomsky, is currently one of the approaches to children's
acquisition of syntax.[16]
The leading idea is that human biology imposes narrow constraints on the
child's "hypothesis space" during language acquisition. In the
Principles and Parameters Framework, which has dominated generative
syntax since Chomsky's (1980)
Lectures on Government and Binding: The Pisa Lectures, the
acquisition of syntax resembles ordering from a menu: The human brain
comes equipped with a limited set of choices, from which the child
selects the correct options using her parents' speech, in combination
with the context.[17]
An important argument, which favors the generative approach, is the
Poverty of the stimulus argument. The child's input (a finite number
of sentences encountered by the child, together with information about
the context in which they were uttered) is, in principle, compatible
with an infinite number of conceivable grammars. Moreover, few, if any,
children can rely on
corrective feedback from adults when they make a grammatical error.[18]
Yet, barring situations of medical abnormality or extreme privation, all
the children in a given speech-community converge on very much the same
grammar by the age of about five years. An especially dramatic example
is provided by children who, for medical reasons, are unable to produce
speech, and, therefore, can never be corrected for a grammatical error,
yet, nonetheless, converge on the same grammar as their typically
developing peers, according to comprehension-based tests of grammar.[19][20]
Considerations such as these have led Chomsky,
Jerry Fodor,
Eric Lenneberg and others to argue that the types of grammar the
child needs to consider must be narrowly constrained by human biology
(the
nativist position).[21]
These innate constraints are sometimes referred to as
universal grammar, the human "language faculty", or the "language
instinct".[22]
Empiricism
Although Chomsky's theory of a
generative grammar has been enormously influential in the field of
linguistics since the 1950s, many criticisms of the basic assumptions of
generative theory have been put forth by cognitive-functional
linguistics, who argue that language structure is created through
language use.[23]
These linguists argue that the concept of a
Language Acquisition Device (LAD) is unsupported by evolutionary
anthropology, which tends to show a gradual adaptation of the human
brain and vocal cords to the use of language, rather than a sudden
appearance of a complete set of binary parameters delineating the whole
spectrum of possible grammars ever to have existed and ever to exist.[citation
needed] On the other hand, cognitive-functional
theorists use this anthropological data to show how human beings have
evolved the capacity for grammar and syntax to meet our demand for
linguistic symbols. (Binary parameters are common to digital computers,
but may not be applicable to neurological systems such as the human
brain.)[citation
needed]
Further, the generative theory has several hypothetical constructs
(such as movement, empty categories, complex underlying structures, and
strict binary branching) that cannot possibly be acquired from any
amount of linguistic input. It is unclear that human language is
actually anything like the generative conception of it. Since
language, as imagined by nativists, is unlearnably complex,[citation
needed] subscribers to this theory argue that it
must, therefore, be innate.[citation
needed] A different theory of language, however,
may yield different conclusions. While all theories of language
acquisition posit some degree of innateness, a less convoluted theory
might involve less innate structure and more learning. Under such a
theory of grammar, the input, combined with both general and
language-specific learning capacities, might be sufficient for
acquisition.[citation
needed]
Since 1980, linguists studying children, such as
Melissa Bowerman, and psychologists following
Jean Piaget, like
Elizabeth Bates and Jean Mandler, came to suspect that there may
indeed be many learning processes involved in the acquisition process,
and that ignoring the role of learning may have been a mistake.[citation
needed]
In recent years, the debate surrounding the nativist position has
centered on whether the inborn capabilities are language-specific or
domain-general, such as those that enable the infant to visually make
sense of the world in terms of objects and actions. The anti-nativist
view has many strands, but a frequent theme is that language emerges
from usage in social contexts, using learning mechanisms that are a part
of a general cognitive learning apparatus (which is what is innate).
This position has been championed by
David M W Powers,[24]
Elizabeth Bates,[25]
Catherine Snow,
Anat Ninio,
Brian MacWhinney,
Michael Tomasello,[3]
Michael Ramscar,[26]
William O'Grady,[27]
and others. Philosophers, such as Fiona Cowie[28]
and Barbara Scholz with
Geoffrey Pullum[29]
have also argued against certain nativist claims in support of
empiricism.
The new field of
Cognitive Linguistics has emerged as a specific counter to Chomskian
Generative Grammar and Nativism.
Statistical
learning
Some language acquisition researchers, such as
Elissa Newport, Richard Aslin, and
Jenny Saffran, believe that language acquisition is based primarily
on general
learning mechanisms, namely statistical learning. The development of
connectionist models that are able to successfully learn words and
syntactical conventions[30]
supports the predictions of statistical learning theories of language
acquisition, as do empirical studies of children's learning of words and
syntax.[31]
Statistical learning theory suggests that, when learning language, a
learner would use the natural statistical properties of language to
deduce its structure, including sound patterns, words, and the
beginnings of grammar.[32]
That is, language learners are sensitive to how often syllable
combinations or words occur in relation to other syllables.[33][34][35]
Infants between 21-months-old and 23-months-old are also able to use
statistical learning to develop "lexical categories," such as an animal
category, which later infants map semantic meaning to newly learned
words in the same category. These findings suggest that early experience
listening to language is critical vocabulary acquisition.[36]
The statistical abilities are effective, but also limited by what
qualifies as input, what is done with that input, and by the structure
of the resulting output.[32]
Chunking
Chunking theories of language acquisition constitute a group of
theories related to statistical learning theories, in that they assume
the input from the environment plays an essential role; however, they
postulate different learning mechanisms. The central idea of these
theories is that language development occurs through the incremental
acquisition of meaningful
chunks of elementary constituents, which can be words, phonemes, or
syllables. Recently, this approach has been highly successful in
simulating several phenomena in the acquisition of syntactic categories[37]
and the acquisition of phonological knowledge.[38]
The approach has several features that make it unique: the models are
implemented as computer programs, which enables clear-cut and
quantitative predictions to be made; they learn from naturalistic input,
made of actual child-directed utterances; they produce actual
utterances, which can be compared with children's utterances; and they
have simulated phenomena in several languages, including English,
Spanish, and German.[citation
needed]
Researchers at the
Max Planck Institute for Evolutionary Anthropology have developed a
computer model analyzing early toddler conversations to predict the
structure of later conversations. They showed that toddlers develop
their own individual rules for speaking with slots, into which they
could put certain kinds of words. A significant outcome of the research
was that rules inferred from toddler speech were better predictors of
subsequent speech than traditional grammars.[39]
Representation of language acquisition in the brain
Recent advances in functional
neuroimaging technology have allowed for a better understanding of
how language acquisition is manifested physically in the brain. Language
acquisition almost always occurs in children during a period of rapid
increase in brain volume. At this point in development, a child has many
more neural connections than he or she will have as an adult, allowing
for the child to be more able to learn new things than he or she would
be as an adult.
Sensitive period
Language acquisition has been studied from the perspective of
developmental psychology and
neuroscience,[citation
needed] which looks at learning to use and
understand language parallel to a child's brain development. It has been
determined, through empirical research on developmentally normal
children, as well as through some extreme cases of language deprivation,
that there is a "sensitive
period" of language acquisition in which human infants have the
ability to learn any language. Several findings have observed that from
birth until the age of six months, infants can discriminate the phonetic
contrasts of all languages. Researchers believe that this gives infants
the ability to acquire the language spoken around them. After this age
the child is only able to perceive the phonemes specific to the language
he or she is learning. This reduced phonemic sensitivity enables
children to build phonemic categories and recognize stress patterns and
sound combinations specific to the language they are acquiring.[40]
As Christophe Pallier noted, "Before the child begins to speak and to
perceive, the uncommitted cortex is a blank slate on which nothing has
been written. In the ensuing years much is written, and the writing is
normally never erased. After the age of ten or twelve, the general
functional connexions have been established and fixed for the speech
cortex." According to the sensitive or critical period models, the age
at which a child acquires the ability to use language is a predictor of
how well he or she is ultimately able to use language.[41]
However, there may be an age at which becoming a fluent and natural user
of a language is no longer possible.[citation
needed] Our brains may be automatically wired to
learn languages,[citation
needed] but this ability does not last into
adulthood in the same way that it exists during development.[citation
needed] By the onset of puberty (around age 12),
language acquisition has typically been solidified and it becomes more
difficult to learn a language in the same way a native speaker would.[citation
needed] At this point, it is usually a second
language that a person is trying to acquire and not a first.[4]
This critical period is usually never missed by cognitively normal
children—humans are so well prepared to learn language that it becomes
almost impossible not to. Researchers are unable to experimentally test
the effects of the sensitive period of development on language
acquisition, because it would be unethical to deprive children of
language until this period is over. However, case studies on abused,
language deprived
children show that they were extremely limited in their language
skills, even after instruction.[42]
At a very young age, children can already distinguish between
different sounds but cannot produce them yet. However, during infancy,
children do begin to babble. Deaf babies babble in the same order when
hearing sounds as non-deaf babies do, thus showing that babbling is not
caused by babies simply imitating certain sounds, but is actually a
natural part of the process of language development. However, deaf
babies do often babble less than non-deaf babies and they begin to
babble later on in infancy (begin babbling at 11 months as compared to 6
months) when compared to non-deaf babies.[43]
Vocabulary
acquisition
The capacity to acquire the ability to incorporate the pronunciation
of new words depends upon many factors. Before anything the learner
needs to be able to hear what they are attempting to pronounce. Another
is the capacity to engage in
speech repetition.[44][45][46][47]
Children with reduced abilities to repeat nonwords (a marker of speech
repetition abilities) show a slower rate of vocabulary expansion than
children for whom this is easy.[48]
It has been proposed that the elementary units of speech have been
selected to enhance the ease with which sound and visual input can be
mapped into motor vocalization.[49]
Several computational models of vocabulary acquisition have been
proposed so far.[50][51][52][53][54][55][56]
Various studies have shown that the size of a child's vocabulary by the
age of 24 months correlates with the child's future development and
language skills. A lack of language richness by this age has detrimental
and long-term effects on the child's cognitive development, which is why
it is so important for parents to engage their infants in language. If a
child knows fifty words or less by the age of 24 months, he or she is
classified as a "late-talker" and future language development, like
vocabulary expansion and the organization of grammar, is likely to be
slower and stunted.[citation
needed]
Two more crucial elements of vocabulary acquisition are word
segmentation and statistical learning (described above). Word
segmentation, or the segmentation of words and syllables from fluent
speech can be accomplished by eight-month-old infants.[33]
By the time infants are 17-months-old, they are able to link meaning to
segmented words.[34]
Meaning
Children learn, on average, ten to fifteen new word meanings each
day, but only one of these words can be accounted for by direct
instruction.[57]
The other nine to fourteen word meanings need to be picked up in some
other way. It has been proposed that children acquire these meanings
with the use of processes modeled by
latent semantic analysis; that is, when they meet an unfamiliar
word, children can use information in its context to correctly guess its
rough area of meaning.[57]
There is also reason to believe that children use various
heuristics to properly infer the meaning of words.
Markman and others have proposed that children assume words to refer
to objects with similar properties (e.g., "cow" and "pig" might both be
"animals") rather than to objects that are thematically related (e.g.,
"cow" and "milk" are probably not both "animals").[58]
Children also seem to adhere to the "whole object assumption" — thinking
that a novel label refers to an entire entity rather than one of its
parts.[58]
Neurocognitive research
According to several linguists, neurocognitive research has confirmed
many standards of language learning, such as: "learning engages the
entire person (cognitive, affective, and psychomotor domains), the human
brain seeks patterns in its searching for meaning, emotions affect all
aspects of learning, retention and recall, past experience always
affects new learning, the brain's working memory has a limited capacity,
lecture usually results in the lowest degree of retention, rehearsal is
essential for retention, practice [alone] does not make perfect, and
each brain is unique" (Sousa, 2006, p. 274). In terms of genetics, the
gene ROBO1
has been associated with phonological buffer integrity or length.[59]
Although it is difficult to determine without invasive measures which
exact parts of the brain become most active and important for language
acquisition,
fMRI and
PET technology has allowed for some conclusions to be made about
where language may be centered.
Kuniyoshi Sakai proposed, based on several neuroimaging studies,
that there may be a "grammar center", where language is primarily
processed in the left lateral
premotor cortex (located near the pre central sulcus and the
inferior frontal sulcus). Additionally, these studies proposed that
first language and second-language acquisition may be represented
differently in the
cortex.[4]
During early infancy, language processing seems to occur over many
areas in the brain. However, over time, it gradually becomes
concentrated into two areas -
Broca's area and
Wernicke's area. Broca's area is in the left
frontal cortex and is primarily involved in the production of the
patterns in vocal and sign language. Wernicke's area is in the left
temporal cortex and is primarily involved in language comprehension.
The specialization of these language centers is so extensive that damage
to them results in a critical condition known as aphasia.[60]
Language acquisition and prelingual deafness
Prelingual deafness is defined as hearing loss that occurred at birth
or before an individual has learned to speak. In the United States,
three out of every 1000 children are born deaf or hard of hearing.
Treatment options include using hearing aids to strengthen remaining
sensory cells or cochlear implants to stimulate the hearing nerve
directly. Despite these developments, most prelingually deaf children
are unlikely to develop good speech and speech reception skills.
However, deaf children of deaf parents tend to do better with language,
even though they are isolated from sound and speech. Humans are
biologically equipped for language, which is not limited to spoken
language only. Even though it might be presumed that deaf children
acquire language in different ways since they are not receiving the same
input as hearing children, many research findings indicate that deaf
children acquire language in the same way that hearing children do.[61]
Babies who learn sign language produce signs or gestures that are more
regular and more frequent than hearing babies acquiring spoken language.[62]
Just as hearing babies babble, deaf babies acquiring sign language will
babble with their hands.[62]
Therefore, the acquisition of sign language seems to have the same
developmental track that is seen in hearing children acquiring spoken
language.
Due to recent advances in technology, cochlear implants allow deaf
people to interact with others more efficiently. There are interior and
exposed components that require a medical procedure. Especially those
who receive cochlear implants earlier in life show improvements.[63]
Language growth is exactly the same for normal individuals and those
with cochlear implants,[63]
and speech processing occurs at a more rapid pace than with traditional
hearing aids.[63]
See also