Computational models of language acquisition
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Statistical language acquisition, a branch of
developmental Development of the human body is the process of growth to maturity. The process begins with fertilization, where an egg released from the ovary of a female is penetrated by a sperm cell from a male. The resulting zygote develops through mitosi ...
psycholinguistics, studies the process by which humans develop the ability to perceive, produce, comprehend, and communicate with natural language in all of its aspects (
phonological Phonology is the branch of linguistics that studies how languages or dialects systematically organize their sounds or, for sign languages, their constituent parts of signs. The term can also refer specifically to the sound or sign system of a ...
, syntactic,
lexical Lexical may refer to: Linguistics * Lexical corpus or lexis, a complete set of all words in a language * Lexical item, a basic unit of lexicographical classification * Lexicon, the vocabulary of a person, language, or branch of knowledge * Lex ...
, morphological, semantic) through the use of general learning mechanisms operating on statistical patterns in the linguistic input. Statistical learning acquisition claims that infants language learning is based on pattern perception rather than an innate biological grammar. Several statistical elements such as frequency of words, frequent frames, phonotactic patterns and other regularities provide information on language structure and meaning for facilitation of language acquisition.


Philosophy

Fundamental to the study of statistical language acquisition is the centuries-old debate between
rationalism In philosophy, rationalism is the epistemological view that "regards reason as the chief source and test of knowledge" or "any view appealing to reason as a source of knowledge or justification".Lacey, A.R. (1996), ''A Dictionary of Philosophy ...
(or its modern manifestation in the psycholinguistic community, nativism) and empiricism, with researchers in this field falling strongly in support of the latter category. Nativism is the position that humans are born with innate
domain-specific Domain specificity is a theoretical position in cognitive science (especially modern cognitive development) that argues that many aspects of cognition are supported by specialized, presumably evolutionarily specified, learning devices. The posit ...
knowledge, especially inborn capacities for language learning. Ranging from seventeenth century rationalist philosophers such as Descartes,
Spinoza Baruch (de) Spinoza (born Bento de Espinosa; later as an author and a correspondent ''Benedictus de Spinoza'', anglicized to ''Benedict de Spinoza''; 24 November 1632 – 21 February 1677) was a Dutch philosopher of Portuguese-Jewish origin, ...
, and
Leibniz Gottfried Wilhelm (von) Leibniz . ( – 14 November 1716) was a German polymath active as a mathematician, philosopher, scientist and diplomat. He is one of the most prominent figures in both the history of philosophy and the history of ma ...
to contemporary philosophers such as
Richard Montague Richard Merritt Montague (September 20, 1930 – March 7, 1971) was an American mathematician and philosopher who made contributions to mathematical logic and the philosophy of language. He is known for proposing Montague grammar to formalize ...
and linguists such as
Noam Chomsky Avram Noam Chomsky (born December 7, 1928) is an American public intellectual: a linguist, philosopher, cognitive scientist, historian, social critic, and political activist. Sometimes called "the father of modern linguistics", Chomsky i ...
, nativists posit an innate learning mechanism with the specific function of language acquisition.Russell, J. (2004). What is Language Development?: Rationalist, Empiricist, and Pragmatist Approaches to the Acquisition of Syntax. Oxford University Press. In modern times, this debate has largely surrounded Chomsky's support of a
universal grammar Universal grammar (UG), in modern linguistics, is the theory of the genetic component of the language faculty, usually credited to Noam Chomsky. The basic postulate of UG is that there are innate constraints on what the grammar of a possible hu ...
, properties that all natural languages must have, through the controversial postulation of a
language acquisition device The Language Acquisition Device (LAD) is a claim from language acquisition research proposed by Noam Chomsky in the 1960s. The LAD concept is a purported instinctive mental capacity which enables an infant to acquire and produce language. It is ...
(LAD), an instinctive mental 'organ' responsible for language learning which searches all possible language alternatives and chooses the parameters that best match the learner's environmental linguistic input. Much of Chomsky's theory is founded on the
poverty of the stimulus Poverty of the stimulus (POS) is the controversial argument from linguistics that children are not exposed to rich enough data within their linguistic environments to acquire every feature of their language. This is considered evidence contrary to ...
(POTS) argument, the assertion that a child's linguistic data is so limited and corrupted that learning language from this data alone is impossible. As an example, many proponents of POTS claim that because children are never exposed to negative evidence, that is, information about what phrases are ungrammatical, the language structure they learn would not resemble that of correct speech without a language-specific learning mechanism. Chomsky's argument for an internal system responsible for language, biolinguistics, poses a three factor model. "Genetic endowment" allows the infant to extract linguistic info, detect rules, and have universal grammar. "External environment" illuminates the need to interact with others and the benefits of language exposure at an early age. The last factor encompasses the brain properties, learning principles, and computational efficiencies that enable children to pick up on language rapidly using patterns and strategies. Standing in stark contrast to this position is empiricism, the epistemological theory that all knowledge comes from sensory experience. This school of thought often characterizes the nascent mind as a
tabula rasa ''Tabula rasa'' (; "blank slate") is the theory that individuals are born without built-in mental content, and therefore all knowledge comes from experience or perception. Epistemological proponents of ''tabula rasa'' disagree with the doctri ...
, or blank slate, and can in many ways be associated with the nurture perspective of the " nature vs. nurture debate". This viewpoint has a long historical tradition that parallels that of rationalism, beginning with seventeenth century empiricist philosophers such as Locke, Bacon,
Hobbes Thomas Hobbes ( ; 5/15 April 1588 – 4/14 December 1679) was an English philosopher, considered to be one of the founders of modern political philosophy. Hobbes is best known for his 1651 book ''Leviathan'', in which he expounds an influe ...
, and, in the following century, Hume. The basic tenet of empiricism is that information in the environment is structured enough that its patterns are both detectable and extractable by domain-general learning mechanisms. In terms of language acquisition, these patterns can be either linguistic or social in nature. Chomsky is very critical of this empirical theory of language acquisition. He has said, "It's true there's been a lot of work on trying to apply statistical models to various linguistic problems. I think there have been some successes, but a lot of failures." He claims the idea of using statistical methods to acquire language is simply a mimicry of the process, rather than a true understanding of how language is acquired.


Experimental paradigms


Headturn Preference Procedure (HPP)

One of the most used experimental paradigms in investigations of infants' capacities for statistical language acquisition is the Headturn Preference Procedure (HPP), developed by Stanford psychologist
Anne Fernald Anne Fernald is an American psychologist. She serves as the Josephine Knotts Knowles Professor in Human Biology at Stanford University and has been described as "the leading researcher in infant-directed speech". Fernald received a Ph.D. in psyc ...
in 1985 to study infants' preferences for prototypical child-directed speech over normal adult speech. In the classic HPP paradigm, infants are allowed to freely turn their heads and are seated between two speakers with mounted lights. The light of either the right or left speaker then flashes as that speaker provides some type of audial or linguistic input stimulus to the infant. Reliable orientation to a given side is taken to be an indication of a preference for the input associated with that side's speaker. This paradigm has since become increasingly important in the study of infant speech perception, especially for input at levels higher than syllable chunks, though with some modifications, including using the listening times instead of the side preference as the relevant dependent measure.


Conditioned Headturn Procedure

Similar to HPP, the Conditioned Headturn Procedure also makes use of an infant's differential preference for a given side as an indication of a preference for, or more often a familiarity with, the input or speech associated with that side. Used in studies of
prosodic In linguistics, prosody () is concerned with elements of speech that are not individual phonetic segments (vowels and consonants) but are properties of syllables and larger units of speech, including linguistic functions such as intonation, st ...
boundary markers by Gout et al. (2004) and later by Werker in her classic studies of
categorical perception Categorical perception is a phenomenon of perception of distinct categories when there is a gradual change in a variable along a continuum. It was originally observed for auditory stimuli but now found to be applicable to other perceptual modalit ...
of native-language
phoneme In phonology and linguistics, a phoneme () is a unit of sound that can distinguish one word from another in a particular language. For example, in most dialects of English, with the notable exception of the West Midlands and the north-wes ...
s, infants are conditioned by some attractive image or display to look in one of two directions every time a certain input is heard, a whole word in Gout's case and a single phonemic syllable in Werker's. After the conditioning, new or more complex input is then presented to the infant, and their ability to detect the earlier target word or distinguish the input of the two trials is observed by whether they turn their head in expectation of the conditioned display or not.


Anticipatory eye movement

While HPP and the Conditioned Headturn Procedure allow for observations of behavioral responses to stimuli and after the fact inferences about what the subject's expectations must have been to motivate this behavior, the Anticipatory Eye Movement paradigm allows researchers to directly observe a subject's expectations before the event occurs. By
tracking Tracking may refer to: Science and technology Computing * Tracking, in computer graphics, in match moving (insertion of graphics into footage) * Tracking, composing music with music tracker software * Eye tracking, measuring the position of t ...
subjects' eye movements researchers have been able to investigate infant decision-making and the ways in which infants encode and act on probabilistic knowledge to make predictions about their environments. This paradigm also offers the advantage of comparing differences in eye movement behavior across a wider range of ages than others.


Artificial languages

Artificial language Artificial languages are languages of a typically very limited size which emerge either in computer simulations between artificial agents, robot interactions or controlled psychological experiments with humans. They are different from both constr ...
s, that is, small-scale languages that typically have an extremely limited
vocabulary A vocabulary is a set of familiar words within a person's language. A vocabulary, usually developed with age, serves as a useful and fundamental tool for communication and acquiring knowledge. Acquiring an extensive vocabulary is one of the la ...
and simplified
grammar In linguistics, the grammar of a natural language is its set of structural constraints on speakers' or writers' composition of clauses, phrases, and words. The term can also refer to the study of such constraints, a field that includes domain ...
rules, are a commonly used paradigm for
psycholinguistic Psycholinguistics or psychology of language is the study of the interrelation between linguistic factors and psychological aspects. The discipline is mainly concerned with the mechanisms by which language is processed and represented in the mind ...
researchers. Artificial languages allow researchers to isolate variables of interest and wield a greater degree of control over the input the subject will receive. Unfortunately, the overly simplified nature of these languages and the absence of a number of phenomena common to all human natural languages such as
rhythm Rhythm (from Greek , ''rhythmos'', "any regular recurring motion, symmetry") generally means a " movement marked by the regulated succession of strong and weak elements, or of opposite or different conditions". This general meaning of regular re ...
, pitch changes, and sequential regularities raise questions of
external validity External validity is the validity of applying the conclusions of a scientific study outside the context of that study. In other words, it is the extent to which the results of a study can be generalized to and across other situations, people, stim ...
for any findings obtained using this paradigm, even after attempts have been made to increase the complexity and richness of the languages used. The artificial language's lack of complexity or decreased complexity fails to account for a child's need to recognize a given syllable in natural language regardless of the sound variability inherent to natural language, though "it is possible that the complexity of natural language actually facilitates learning."Romberg, A. R., & Saffran, J. R. (2010). Statistical learning and language acquisition. John Wiley & Sons, Ltd. WIREs Cognitive Science. http://www.waisman.wisc.edu/infantlearning/Publications_files/Romberg.Saffran.2010.pdf As such, artificial language experiments are typically conducted to explore what the relevant linguistic variables are, what sources of information infants are able to use and when, and how researchers can go about modeling the learning and acquisition process. Aslin and Newport, for example, have used artificial languages to explore what features of linguistic input make certain
pattern A pattern is a regularity in the world, in human-made design, or in abstract ideas. As such, the elements of a pattern repeat in a predictable manner. A geometric pattern is a kind of pattern formed of geometric shapes and typically repeated li ...
s salient and easily detectable by infants, allowing them to easily contrast the detection of syllable repetition with that of word-final syllables and make conclusions about the conditions under which either feature is recognized as important.


Audio and audiovisual recordings

Statistical learning has been shown to play a large role in language acquisition, but social interaction appears to be a necessary component of learning as well. In one study, infants presented with audio or audiovisual recordings of Mandarin speakers failed to distinguish the phonemes of the language. This implies that simply hearing the sounds is not sufficient for language learning; social interaction cues the infant to take statistics. Particular interactions geared towards infants is known as "child-directed" language because it is more repetitive and associative, which makes it easier to learn. These "child directed" interactions could also be the reason why it is easier to learn a language as a child rather than an adult.


Bilinguals

Studies of bilingual infants, such as a study Bijeljac-Babic, et al., on French-learning infants, have offered insight to the role of prosody in language acquisition. The Bijeljac-Babic study found that language dominance influences "sensitivity to prosodic contrasts." Although this was not a study on statistical learning, its findings on prosodic pattern recognition might have implications for statistical learning. It is possible that the kinds of language experience and knowledge gained through the statistical learning of the first language influences one's acquisition of a second language. Some research points to the possibility that the difficulty of learning a second language may be derived from the structural patterns and language cues that one has already picked up from his or her acquisition of first language. In that sense, the knowledge of and skills to process the first language from statistical acquisition may act as a complicating factor when one tries to learn a new language with different sentence structures, grammatical rules, and speech patterns.


Important findings


Phonetic category learning

The first step in developing knowledge of a system as complex as natural language is learning to distinguish the important language-specific classes of sounds, called phonemes, that distinguish meaning between words.
UBC The University of British Columbia (UBC) is a public research university with campuses near Vancouver and in Kelowna, British Columbia. Established in 1908, it is British Columbia's oldest university. The university ranks among the top three ...
psychologist
Janet Werker Janet F. Werker is a researcher in the field of developmental psychology. She researches the foundations of monolingual and bilingual infant language acquisition in infants at the University of British Columbia's Infant Studies Centre. Her resea ...
, since her influential series of experiments in the 1980s, has been one of the most prominent figures in the effort to understand the process by which human babies develop these phonological distinctions. While adults who speak different languages are unable to distinguish meaningful sound differences in other languages that do not delineate different meanings in their own, babies are born with the ability to universally distinguish all speech sounds. Werker's work has shown that while infants at six to eight months are still able to perceive the difference between certain
Hindi Hindi ( Devanāgarī: or , ), or more precisely Modern Standard Hindi (Devanagari: ), is an Indo-Aryan language spoken chiefly in the Hindi Belt region encompassing parts of northern, central, eastern, and western India. Hindi has been ...
and
English English usually refers to: * English language * English people English may also refer to: Peoples, culture, and language * ''English'', an adjective for something of, from, or related to England ** English national ide ...
consonant In articulatory phonetics, a consonant is a speech sound that is articulated with complete or partial closure of the vocal tract. Examples are and pronounced with the lips; and pronounced with the front of the tongue; and pronounced wi ...
s, they have completely lost this ability by 11 to 13 months. It is now commonly accepted that children use some form of perceptual distributional learning, by which categories are discovered by clumping similar instances of an input stimulus, to form phonetic categories early in life. Developing children have been found to be effective judges of linguistic authority, screening the input they model their language on by shifting their attention less to speakers who mispronounce words. Infants also use statistical tracking to calculate the likelihood that particular phonemes will follow each other. Romberg, Alexa R and Sarron, Jenny R. (2010).
Statistical Learning and Language Acquisition
" WIREs Cogn Sci 10.1002/wbs.78


Parsing

Parsing Parsing, syntax analysis, or syntactic analysis is the process of analyzing a string of symbols, either in natural language, computer languages or data structures, conforming to the rules of a formal grammar. The term ''parsing'' comes from L ...
is the process by which a continuous speech stream is segmented into its
discrete Discrete may refer to: *Discrete particle or quantum in physics, for example in quantum theory *Discrete device, an electronic component with just one circuit element, either passive or active, other than an integrated circuit *Discrete group, a g ...
meaningful units, e.g.
sentences ''The Four Books of Sentences'' (''Libri Quattuor Sententiarum'') is a book of theology written by Peter Lombard in the 12th century. It is a systematic compilation of theology, written around 1150; it derives its name from the '' sententiae'' ...
,
word A word is a basic element of language that carries an objective or practical meaning, can be used on its own, and is uninterruptible. Despite the fact that language speakers often have an intuitive grasp of what a word is, there is no conse ...
s, and syllables. Saffran (1996) represents a singularly seminal study in this line of research. Infants were presented with two minutes of continuous speech of an artificial language from a computerized voice to remove any interference from extraneous variables such as prosody or intonation. After this presentation, infants were able to distinguish words from nonwords, as measured by longer looking times in the second case. An important concept in understanding these results is that of transitional probability, the
likelihood The likelihood function (often simply called the likelihood) represents the probability of random variable realizations conditional on particular values of the statistical parameters. Thus, when evaluated on a given sample, the likelihood functi ...
of an element, in this case a syllable, following or preceding another element. In this experiment, syllables that went together in words had a much higher transitional probability than did syllables at word boundaries that just happened to be adjacent. Incredibly, infants, after a short two-minute presentation, were able to keep track of these statistics and recognize high
probability Probability is the branch of mathematics concerning numerical descriptions of how likely an event is to occur, or how likely it is that a proposition is true. The probability of an event is a number between 0 and 1, where, roughly speakin ...
words. Further research has since replicated these results with natural languages unfamiliar to infants, indicating that learning infants also keep track of the direction (forward or backward) of the transitional probabilities. Though the neural processes behind this phenomenon remain largely unknown, recent research reports increased activity in the left inferior frontal gyrus and the
middle frontal gyrus The middle frontal gyrus makes up about one-third of the frontal lobe of the human brain. (A ''gyrus'' is one of the prominent "bumps" or "ridges" on the surface of the human brain.) The middle frontal gyrus, like the inferior frontal gyrus an ...
during the detection of word boundaries. The development of syllable-ordering biases is an important step along the way to full language development. The ability to categorize syllables and group together frequently co-occurring sequences may be critical in the development of a ''protolexicon'', a set of common language-specific word templates based on characteristic patterns in the words an infant hears. The development of this protolexicon may in turn allow for the recognition of new types of patterns, e.g. the high frequency of word-initially stressed consonants in English, which would allow infants to further parse words by recognizing common prosodic phrasings as autonomous linguistic units, restarting the dynamic cycle of word and language learning.


Referent-label associations

The question of how novice language-users are capable of associating learned
labels A label (as distinct from signage) is a piece of paper, plastic film, cloth, metal, or other material affixed to a container or product, on which is written or printed information or symbols about the product or item. Information printed d ...
with the appropriate referent, the person or object in the environment which the label names, has been at the heart of
philosophical Philosophy (from , ) is the systematized study of general and fundamental questions, such as those about existence, reason, knowledge, values, mind, and language. Such questions are often posed as problems to be studied or resolved. Some ...
considerations of
language Language is a structured system of communication. The structure of a language is its grammar and the free components are its vocabulary. Languages are the primary means by which humans communicate, and may be conveyed through a variety of ...
and meaning from
Plato Plato ( ; grc-gre, Πλάτων ; 428/427 or 424/423 – 348/347 BC) was a Greek philosopher born in Athens during the Classical period in Ancient Greece. He founded the Platonist school of thought and the Academy, the first institution ...
to Quine to Hofstadter. This problem, that of finding some solid relationship between word and object, of finding a word's meaning without succumbing to an infinite recursion of dictionary look-up, is known as the symbol grounding problem. Researchers have shown that this problem is intimately linked with the ability to parse language, and that those words that are easy to segment due to their high transitional probabilities are also easier to
map A map is a symbolic depiction emphasizing relationships between elements of some space, such as objects, regions, or themes. Many maps are static, fixed to paper or some other durable medium, while others are dynamic or interactive. Although ...
to an appropriate referent. This serves as further evidence of the developmental progression of language acquisition, with children requiring an understanding of the sound distributions of natural languages to form phonetic categories, parse words based on these categories, and then use these parses to map them to objects as labels. The developmentally earliest understanding of word to referent associations have been reported at six months old, with infants comprehending the words ' mommy' and '
daddy A father is the male parent of a child. Besides the paternal bonds of a father to his children, the father may have a parental, legal, and social relationship with the child that carries with it certain rights and obligations. An adoptive fathe ...
' or their familial or cultural equivalents. Further studies have shown that infants quickly develop in this capacity and by seven months are capable of learning associations between moving images and
nonsense Nonsense is a communication, via speech, writing, or any other symbolic system, that lacks any coherent meaning. Sometimes in ordinary usage, nonsense is synonymous with absurdity or the ridiculous. Many poets, novelists and songwriters have u ...
words and syllables. It is important to note that there is a distinction, often confounded in acquisition research, between mapping a label to a specific instance or individual and mapping a label to an entire class of objects. This latter process is sometimes referred to as
generalization A generalization is a form of abstraction whereby common properties of specific instances are formulated as general concepts or claims. Generalizations posit the existence of a domain or set of elements, as well as one or more common characte ...
or rule learning. Research has shown that if input is encoded in terms of perceptually salient dimensions rather than specific details and if patterns in the input indicate that a number of objects are named interchangeably in the same context, a language learner will be much more likely to generalize that name to every instance with the relevant features. This tendency is heavily dependent on the consistency of context clues and the degree to which word contexts overlap in the input. These differences are furthermore linked to the well-known patterns of under and overgeneralization in infant word learning. Research has also shown that the frequency in co-occurrence of referents is tracked as well, which helps create associations and dispel ambiguities in object-referent models. The ability to appropriately generalize to whole classes of yet unseen words, coupled with the abilities to parse continuous speech and keep track of word-ordering regularities, may be the critical skills necessary to develop proficiency with and knowledge of syntax and grammar.


Differences in autistic populations

According to recent research, there is no neural evidence of statistical language learning in children with
autism spectrum disorders The autism spectrum, often referred to as just autism or in the context of a professional diagnosis autism spectrum disorder (ASD) or autism spectrum condition (ASC), is a neurodevelopmental condition (or conditions) characterized by difficulti ...
. When exposed to a continuous stream of artificial speech, neurotypical children displayed less cortical activity in the dorsolateral frontal cortices (specifically the
middle frontal gyrus The middle frontal gyrus makes up about one-third of the frontal lobe of the human brain. (A ''gyrus'' is one of the prominent "bumps" or "ridges" on the surface of the human brain.) The middle frontal gyrus, like the inferior frontal gyrus an ...
) as cues for word boundaries increased. However activity in these networks remained unchanged in autistic children, regardless of the verbal cues provided. This evidence, highlighting the importance of proper Frontal Lobe brain function is in support of the "Executive Functions" Theory, used to explain some of the biologically related causes of Autistic language deficits. With impaired working memory, decision making, planning, and goal setting, which are vital functions of the Frontal Lobe, Autistic children are at loss when it comes to socializing and communication (Ozonoff, et al., 2004). Additionally, researchers have found that the level of communicative impairment in autistic children was inversely correlated with signal increases in these same regions during exposure to artificial languages. Based on this evidence, researchers have concluded that children with autism spectrum disorders don't have the neural architecture to identify word boundaries in continuous speech. Early word segmentation skills have been shown to predict later language development, which could explain why language delay is a hallmark feature of autism spectrum disorders.


Statistical language learning across situations

Language learning takes place in different contexts, with both the infant and the caregiver engaging in social interactions. Recent research have investigated how infants and adults use cross-situational statistics in order to learn about not only the meanings of words but also the constraints within a context. For example, Smith and his colleagues proposed that infants learn language by acquiring a bias to label objects to similar objects that come from categories that are well-defined. Important to this view is the idea that the constraints that assist learning of words are not independent of the input itself or the infant's experience. Rather, constraints come about as infants learn about the ways that the words are used and begin to pay attention to certain characteristics of objects that have been used in the past to represent the words. Inductive learning problem can occur as words are oftentimes used in ambiguous situations in which there are more than one possible referents available. This can lead to confusion for the infants as they may not be able to distinguish which words should be extended to label objects being referenced to. Smith and Yu proposed that a way to make a distinction in such ambiguous situations is to track the word-referent pairings over multiple scenes. For instance, an infant who hears a word in the presence of object A and object B will be unsure of whether the word is the referent of object A or object B. However, if the infant then hears the label again in the presence of object B and object C, the infant can conclude that object B is the referent of the label because object B consistently pairs with the label across different situations.


Computational models

Computational model A computational model uses computer programs to simulate and study complex systems using an algorithmic or mechanistic approach and is widely used in a diverse range of fields spanning from physics, chemistry and biology to economics, psychology, ...
s have long been used to explore the mechanisms by which language learners process and manipulate linguistic
information Information is an abstract concept that refers to that which has the power to inform. At the most fundamental level information pertains to the interpretation of that which may be sensed. Any natural process that is not completely random ...
. Models of this type allow researchers to systematically control important learning variables that are oftentimes difficult to manipulate at all in human participants.Zinszer, B. & Li, P. (2010)
A SOM model of first language lexical attrition
In S. Ohlsson & R. Catrambone (Eds.), Proceedings of the 32nd Annual Conference of the Cognitive Science Society (pp. 2787-2792). Austin, TX: Cognitive Science Society.


Associative models

Associative neural network models of language acquisition are one of the oldest types of
cognitive model A cognitive model is an approximation of one or more cognitive processes in humans or other animals for the purposes of comprehension and prediction. There are many types of cognitive models, and they can range from box-and-arrow diagrams to a set ...
, using distributed representations and changes in the weights of the connections between the nodes that make up these representations to simulate learning in a manner reminiscent of the plasticity-based
neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. ...
al reorganization that forms the basis of human learning and
memory Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered ...
. Associative models represent a break with classical cognitive models, characterized by discrete and context-free symbols, in favor of a
dynamical system In mathematics, a dynamical system is a system in which a function describes the time dependence of a point in an ambient space. Examples include the mathematical models that describe the swinging of a clock pendulum, the flow of water in ...
s approach to language better capable of handling temporal considerations. A precursor to this approach, and one of the first model types to account for the dimension of time in linguistic comprehension and production was Elman's simple recurrent network (SRN). By making use of a feedback network to represent the system's past states, SRNs were able in a word-prediction task to cluster input into self-organized grammatical categories based solely on statistical co-occurrence patterns.Elman, J. L. (1975). Language as a dynamical system. Most. Early successes such as these paved the way for dynamical systems research into linguistic acquisition, answering many questions about early linguistic development but leaving many others unanswered, such as how these statistically acquired lexemes are represented. Of particular importance in recent research has been the effort to understand the dynamic interaction of learning (e.g. language-based) and learner (e.g. speaker-based) variables in lexical organization and
competition Competition is a rivalry where two or more parties strive for a common goal which cannot be shared: where one's gain is the other's loss (an example of which is a zero-sum game). Competition can arise between entities such as organisms, indiv ...
in bilinguals. In the ceaseless effort to move toward more psychologically realistic models, many researchers have turned to a subset of associative models,
self-organizing map A self-organizing map (SOM) or self-organizing feature map (SOFM) is an unsupervised machine learning technique used to produce a low-dimensional (typically two-dimensional) representation of a higher dimensional data set while preserving the t ...
s (SOMs), as established, cognitively plausible models of language development. SOMs have been helpful to researchers in identifying and investigating the constraints and variables of interest in a number of acquisition processes, and in exploring the consequences of these findings on linguistic and cognitive theories. By identifying
working memory Working memory is a cognitive system with a limited capacity that can hold information temporarily. It is important for reasoning and the guidance of decision-making and behavior. Working memory is often used synonymously with short-term memory, ...
as an important constraint both for language learners and for current computational models, researchers have been able to show that manipulation of this variable allows for
syntactic bootstrapping Syntactic bootstrapping is a theory in developmental psycholinguistics and language acquisition which proposes that children learn word meanings by recognizing syntactic categories (such as nouns, adjectives, etc.) and the structure of their langua ...
, drawing not just categorical but actual content meaning from words' positional co-occurrence in sentences.


Probabilistic models

Some recent models of language acquisition have centered around methods of Bayesian Inference to account for infants' abilities to appropriately parse streams of speech and acquire word meanings. Models of this type rely heavily on the notion of
conditional probability In probability theory, conditional probability is a measure of the probability of an event occurring, given that another event (by assumption, presumption, assertion or evidence) has already occurred. This particular method relies on event B occu ...
(the probability of A given B), in line with findings concerning infants' use of transitional probabilities of words and syllables to learn words. Models that make use of these probabilistic methods have been able to merge the previously
dichotomous A dichotomy is a partition of a whole (or a set) into two parts (subsets). In other words, this couple of parts must be * jointly exhaustive: everything must belong to one part or the other, and * mutually exclusive: nothing can belong simult ...
language acquisition perspectives of
social theories Social theories are analytical frameworks, or paradigms, that are used to study and interpret social phenomenon, social phenomena.Seidman, S., 2016. Contested knowledge: Social theory today. John Wiley & Sons. A tool used by social scientists, so ...
that emphasize the importance of learning speaker intentions and statistical and associative theories that rely on cross-situational contexts into a single joint-inference problem. This approach has led to important results in explaining acquisition phenomena such as
mutual exclusivity In logic and probability theory, two events (or propositions) are mutually exclusive or disjoint if they cannot both occur at the same time. A clear example is the set of outcomes of a single coin toss, which can result in either heads or tails ...
, one-trial learning or fast mapping, and the use of social intentions. While these results seem to be robust, studies concerning these models' abilities to handle more complex situations such as multiple referent to single label mapping, multiple label to single referent mapping, and bilingual language acquisition in comparison to associative models' successes in these areas have yet to be explored. Hope remains, though, that these model types may be merged to provide a comprehensive account of language acquisition.


C/V hypothesis

Along the lines of probabilistic frequencies, the C/V hypothesis basically states all language hearers use consonantal frequencies to distinguish between words (lexical distinctions) in continuous speech strings, in comparison to vowels. Vowels are more pertinent to rhythmic identification. Several follow-up studies revealed this finding, as they showed that vowels are processed independently of their local statistical distribution. Other research has shown that the consonant-vowel ratio doesn't influence the sizes of lexicons when comparing distinct languages. In the case of languages with a higher consonant ratio, children may depend more on consonant neighbors than rhyme or vowel frequency.


Algorithms for language acquisition

Some models of language acquisition have been based on adaptive parsing and
grammar induction Grammar induction (or grammatical inference) is the process in machine learning of learning a formal grammar (usually as a collection of ''re-write rules'' or '' productions'' or alternatively as a finite state machine or automaton of some kind) fr ...
algorithms.Chater, Nick, and Christopher D. Manning.
Probabilistic models of language processing and acquisition
" Trends in cognitive sciences 10.7 (2006): 335-344.


References

{{DEFAULTSORT:Statistical Language Acquisition Language acquisition Applied linguistics