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Multiunit sequences in first language acquisition

DOI:10.1111/tops.12268

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Citation for published version (APA):Theakston, A., & Lieven, E. (2017). Multiunit sequences in first language acquisition. Topics in Cognitive Science.https://doi.org/10.1111/tops.12268

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Multiunit Sequences in First Language Acquisition1

Anna Theakston

and

Elena Lieven

ESRC International Centre for Language and Communicative Development

University of Manchester, UK

Acknowledgements: Anna Theakston and Elena Lieven are Professors in the International

Centre for Language and Communicative Development (LuCiD) at The University of

Manchester. The support of the Economic and Social Research Council [ES/L008955/1] is

gratefully acknowledged.

Abstract

Theoretical and empirical reasons suggest that children build their language not only out of

individual words but also out of multiunit strings. These are the basis for the development of

schemas containing slots. The slots are putative categories which build in abstraction while

the schemas eventually connect to other schemas in terms of both meaning and form. Evi-

dence comes from the nature of the input, the ways in which children construct novel utter-

ances, the systematic errors that children make, and the computational modelling of chil-

dren’s grammars. However, much of this research is on English, which is unusual in its rigid

word order and impoverished inflectional morphology. We summarise these results and ex-

plore their implications for languages with more flexible word order and/or much richer in-

flectional morphology.

1 Address for correspondence: Elena Lieven, Child Study Centre, Coupland 1 Building,

University of Manchester. M13 9PL, UK. Email: elena.lieven@manchester.ac.uk

2

Multiunit Strings in First Language Acquisition

Introduction

The use of frequent multiunit strings in written and spoken language is well established and is

associated with a range of processing advantages (Wray, 2012). These strings can be fully

specified (e.g. How are you? Don’t know, Bybee & Scheibmann, 1999) or more flexible with

slots of varying abstractness (X found X’s way PP, X let alone Y, Fillmore, Kay & O’Connor

1988). The question we address in this paper is the role that multiunit strings of differing

degrees of abstraction might play in the learning of grammatical structure in first language

acquisition. By ‘abstractness’ and ‘abstraction’, we mean any slot in a string that goes beyond

a specific phonological form or word. So, for example, a child’s lexicon might initially

contain a frozen phrase such as Where’s Daddy? before adding Where’s PERSON? and then

Where’s PERSON/OBJECT?, ending up with Where’s NP?. During this process of

developing slots of increasingly wider scope within schemas, the X slot in the Where’s X?

schema has increased in abstractness.2

The role of multiunit strings in first language acquisition

From a usage-based theoretical perspective, our ability to understand and create novel

utterances derives from the fact that they are like utterances we have heard and used before.

Thus we can think of the task of language learning as learning to appropriately reuse the

language that one hears. Researchers working within a usage-based perspective argue that

multiunit strings form one important starting point in the language acquisition process. If

multiunit strings occur frequently enough in the input, then it is possible for children to learn

and use them. There are also good theoretical arguments for the idea that storing strings as

well as words is computationally efficient provided there is enough redundancy in the system

(Bannard & Lieven 2009). The process of abstraction is then thought to build on this early

learning. Multiunit strings provide an opportunity for children to dissect and recombine

linguistic elements, and to create more abstract frames by generalizing across lexical items;

these strings in turn eventually link up to create an adult-like grammar (e.g. Lieven, Salomo

& Tomasello 2009).

2 We use CAPS for the content of a slot and italics to denote a schema or utterance

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For the usage-based approach to work, three important criteria must be met. First, if children

are to learn multiunit strings, these must exist in substantial numbers in the language that they

hear. Second, we need evidence that at least some of children’s early language is based on

these multiunit strings. Third, we need to demonstrate that multiunit strings facilitate the

development of more abstract linguistic representations, which explains how, based on

strings that they hear, children can produce novel utterances. Here, we take English as a test

case for these processes, before considering their application cross-linguistically.

Multiunit strings in English

English, as a language which is governed by strict word order and does not allow argument

ellipsis (except in certain pragmatically motivated contexts), lends itself to the acquisition of

multiunit sequences. Previous studies show that the language English-speaking children are

exposed to contains large numbers of multiunit collocations.

Input

Bannard and Matthews (2008) computed the frequency of 1-5 word strings in child-directed-

speech (CDS) and found many strings that were at least as frequent as individual words in the

core lexicon. This gives prima facie support to the suggestion that some multiunit strings are

highly frequent and available for children to learn. In a more detailed analysis of the speech

addressed to 12 English-learning children between the ages of 2-3 years, Cameron-Faulkner,

Lieven, and Tomasello (2003) found that half of the utterances addressed to the children

could be characterised by 52 item-based frames, with 45% beginning with one of just 17

different words. They argued that the distributional properties of the input were conducive to

children’s acquisition of lexical frames, and that repeated exposure to these frames could

provide a route into the more abstract linguistic system: “Whatever else it is, the acquisition

of a language is the acquisition of a skill, and skills are crucially dependent on repetition and

repetition with variation” (2003, p. 868).

Evidence for frames in early English child language

It is now well established, starting with the work of Braine (1976) and Peters (1983), that

children’s early utterances are less complex and more lexically-specific than those of adult

speakers. Our own work and that of our colleagues demonstrates that a large proportion of

children’s early utterances can be accounted for by a small number of high frequency frames

based around specific lexical items or multiunit chunks (e.g. I’m V-ing it, It’s a X, What can

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X?, Where’s X?, Lieven, Pine, & Baldwin, 1997). Supporting evidence exists in a range of

linguistic domains including children’s early use of auxiliary verbs (Theakston, Lieven, Pine,

& Rowland, 2005), determiners (Pine, Freudenthal, Krajewski & Gobet, 2013), wh-questions

(Rowland & Pine, 2000), and grammatical constructions such as the transitive (Theakston,

Maslen, Lieven, & Tomasello, 2012). Many of the frames identified in early child speech

occur with high frequency in the input addressed to children (Cameron-Faulkner et al., 2003).

Further studies have found that the schemas used in early child language appear to exist

relatively independently of one another, at least in the earliest stages. They show relatively

little overlap in their content, for example with respect to the main verbs produced with

different auxiliaries (can’t X vs. don’t Y, Lieven, 2008) and the nouns used with particular

determiners (a X vs. the Y, Pine et al., 2013). These schemas may be individually learned

from the input and, initially at least, contain lexically and/or semantically restricted slots.

Another, more direct, source of evidence for children’s learning and storage of multiunit

sequences is the finding that children are better able to repeat four-word sequences found

frequently in CDS than less frequent four-word sequences, even when the frequency of the

individual items and bigrams is carefully controlled (e.g. compare a cup of tea with a cup of

milk, Bannard & Matthews, 2008).

Finally, there is evidence that children (and sometimes adults) appear to rely on lexically-

based frames in the production of complex utterances. Diessel and Tomasello (2001) reported

that children’s earliest complement clauses are organised around only a small number of

main verbs often occurring with specific subject arguments too, for example I

think+COMPLEMENT. These kinds of schemas also extend into children’s and adults’ use

of complex questions. Questions beginning with high frequency chunks such as What do you

think…? were repeated more accurately than those with the same syntactic structure and

vocabulary, but beginning with an infrequent sequence such as What does the old man

think…? (Dąbrowska, Rowland & Theakston, 2009).

Role of multiunit strings in abstraction, productivity and creativity

We envisage children’s linguistic systems building up as a network of constructions which

become increasingly interconnected along a range of dimensions: phonological, prosodic,

semantic, pragmatic and structural. For example, from early on English-speaking children

develop considerable flexibility with nouns such that they can use them across a number of

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different schemas: I want a X, That’s a X. Initially this putative noun category may be quite

low-scope e.g. of objects and/or people, and this may vary from child to child. But as

children learn more and more constructions, the mapping of the semantics of ‘ENTITY’ to

‘noun phrase’ will become increasingly abstract, i.e. will lose much of its phonological and

semantic specificity, ultimately allowing for the insertion of relative clauses, clefts etc.

One way to examine the process of abstraction is to look at how early-produced utterances

are subsequently modified to produce longer, more complex sequences. If children are storing

prefabricated chunks of language, then earlier learned words might be expected to appear in

more complex utterances than later learned words, because the child has had the opportunity

to gradually increase the length of the sequences learned from the input. Furthermore, if

there is lexical overlap between earlier and later utterances, this might suggest that rather than

constructing utterances from scratch by combining abstract semantic or grammatical

categories, children are instead accessing prefabricated strings which they then combine with

other words/strings to build complexity. These strings may function to free up the child’s

processing resources as a result of automatization in memory or greater ease of retrieval

(Logan, 1988), enabling them to extend their earlier productions.

In diary data from one child, Tomasello (1992) observed that there was added-value in her

verb use over development as a function of her earlier uses of those same verbs. Verbs

tended to be combined with the same kinds of arguments (e.g. actor, object) as they had been

previously, with new arguments added over time. Complexity reflected their cumulative

frequency of use but varied from one verb to the next, suggesting that their representations

were not fully interconnected. Testing this claim more widely, McClure, Pine, and Lieven

(2006) found that for 12 English-learning children between 2-3 years, verb utterances

produced at MLU 2.0-2.49 were more complex for verbs that had been used previously and

consequently had a higher cumulative frequency of use, than for newly acquired verbs, while

Theakston et al., (2012), in a case study using densely sampled data, found that from age 2;0-

2;6, 79% of the verbs the child used in a full subject-verb-object construction had previously

been used in a simpler subject-verb or verb-object construction, many with the same subject

and/or object arguments.

Further evidence for the process of using multiunit strings comes from a series of studies that

attempted to derive later utterances from those heard or produced earlier in development. In a

6

study of two children’s early utterances, Lieven et al. (2009) found that at 2;0 many of the

children’s apparently novel utterances could be formed by making only minor changes to

their previous utterances. In a more robust test of this process, frequency-driven grammars

derived from child speech using a Bayesian computational model (Bannard, Lieven, &

Tomasello, 2009) were demonstrated to provide a better fit to children’s early utterances than

a more abstract grammar incorporating broad categories like Noun and Verb. However, by

3;0, introducing these categories made a significant difference to the goodness of fit.

A further source of evidence for the role of low-scope, multiunit strings in the development

of abstraction is the gradual convergence between child and adult language, as children

acquire greater flexibility in language use. In a recent study, Theakston, Ibbotson,

Freudenthal, Lieven & Tomasello (2015) examined the degree of overlap in the nouns used

as Subject and Object between children’s and their caregivers’ Subject-Verb-Object

combinations at 2 and 3 years of age, with the application of controls for vocabulary and

sample size. Over development, both the degree of lexical overlap between mother and child

in the nouns used with a given verb, and the degree of items uniquely attested in the

children’s speech increased, demonstrating both abstraction in the slots, and convergence on

the adult grammar. In summary, for English at least, children’s acquisition of lexical

collocations and low-scope variable frames appears to provide one plausible route into more

abstract and general grammatical representations.

The role of pronouns in abstraction

Multiunit strings can be sequential but there is also ample evidence that they can be created

around variable slots, for example in the frame Where’s X gone?. We know that infants are

better able to detect non-adjacent patterns in strings of syllables if there is sufficient variation

in an intervening element between two relatively stable anchors (Gomez, 2002), and in older

children there is some evidence that constructions modelled with a number of different verbs

facilitate generalisation to new verbs (Savage, Lieven, Theakston & Tomasello, 2006). In the

creation of these slot-and-frame patterns, pronouns have been observed to play a privileged

role as anchors around a variable verb slot. For example, pronouns account for over 80% of

transitive subjects in the input to young English-speaking children (Cameron-Faulkner et al.,

2003) and thus may support the acquisition of schemas such as He’s V-ing it, into which new

verbs can be inserted. Evidence for this suggestion comes from multiple sources:

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when children corrected sentences with novel verbs presented in non-English word

orders (SOV - The fox the bear tammed), roughly half of the time they did so using

pronoun subjects and objects (Akhtar, 1999)

children show sensitivity to the form and placing of pronouns in their interpretation

of transitive sentences (Ibbotson, Theakston, Lieven & Tomasello, 2011)

in our dense data analysis of one child’s early transitive SVO use between age 2;4-

2;6, over 75% of objects were represented by the pronoun it (Theakston et al., 2012)

although children can generalise the SVO construction to a novel verb when exposed

to hundreds of examples with known verbs, generalisation improves if these models

include pronominal as well as lexical subjects and objects (Childers & Tomasello,

2001)

a computational model of early language exposed to child-directed-speech

spontaneously generated pronoun islands of organisation based on frequency of

exposure (Jones, Gobet, & Pine, 2000)

Thus, because pronouns are both frequent and systematically ordered in strings, they afford

not only the earlier learning of these strings but also the creation of increasingly abstract slots

preceding or following them. Because they are a closed set with extensive interconnections

across the child’s developing system, they allow for earlier, more sophisticated production

and comprehension than is shown with lexical nouns.

The role of multiunit strings in children’s errors

Children’s errors are an important test for the role of multiunit strings in acquisition, since

adults will not produce these errors. High frequency strings can both protect from error (and

conversely explain why children make more errors with strings of lower frequency), and lead

to error when children utilise them in the wrong contexts (Ambridge, Kidd, Rowland &

Theakston, 2015).

Evidence that high frequency strings can protect from errors comes from a number of studies.

For inflectional morphology, Arnon & Clark (2011) found that children produced irregular

plurals (e.g. mice) more accurately, avoiding overregularisation errors (e.g. mouses), when

they were part of strings such as ‘Three blind …’ than after unrelated high frequency strings

(So many …). In unpublished work, we found similar results for irregular past tense forms. In

8

corpus data from 19 children between 2;0-3;6, overregularisation errors (e.g. run-ed)

occurred significantly less often as part of high frequency three-word strings (defined from

collocations with the target verbs in CDS) than did correct utterances with those same verbs.

In wh- and yes-no-questions, where the required wh+auxiliary or auxiliary+pronoun

combination is frequent in the input, children produce fewer uninversion (e.g. *What he can

do?) and double marking errors (e.g. *Can he can’t go to the park?), than for questions

without a high frequency frame (Ambridge & Rowland, 2009; Rowland & Pine, 2000, see

Dąbrowska et al., 2009 on complex questions).

Sometimes, children appear to learn multiple strings from the input which then compete for

activation, leading to errors when they are used in inappropriate contexts. The likelihood of

any given string being produced depends on a number of factors including the relative

frequency of the competing strings in the input, and which string has most recently been

primed for retrieval. For example, in both typical and atypical language development

(Theakston & Lieven, 2008; Leonard & Deevy, 2011), apparently optional use of tense and

agreement markers is influenced by the input. Children who hear subject-verb strings with

no intervening auxiliary as part of a more complex utterance (e.g. Are you keefing?) produce

lower levels of auxiliary verb provision in their subsequent declaratives (You keefing).

Children’s erroneous use of me instead of I as the subject of sentences (e.g. *Me do it) can be

explained in a similar way as competition between a me-verb and I-verb frame. Kirjavainen,

Theakston, and Lieven (2009) showed that 2-3-year-old children’s production of me-for-I

errors was related to the relative rate at which their caregivers produced complex sentences in

which the accusative pronoun me appeared pre-verbally (e.g. Let me do it). Furthermore, the

verbs that children used erroneously with me were significantly more likely to occur in their

caregivers’ speech with pre-verbal me than those used correctly (see Kirjavainen, Lieven &

Theakston, in press for a similar account of infinitival-to omissions). In all of these

examples, the assumption is that errors are gradually eradicated as children build up

representations of the appropriate complex sentence structures, thus reducing the activation of

erroneous competing forms for simple sentences.

However, children also produce many utterances which cannot be a direct ‘reading off’ from

the input (e.g. *Me can’t do it, *Why can it can’t fit?), suggesting that children move beyond

simple repetition of strings to create more abstract slot-and-frame patterns from a legitimate

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use in the input which they then use productively, resulting in error. Accounting for the

productivity which leads to errors is critical, and although high frequency strings can get us

so far in explaining children’s correct uses and errors, there is a clear need for multifaceted

models of acquisition to move us beyond a simple reliance on early learned schemas based

directly on the input children hear (Ambridge, et al. 2015).

In some areas of acquisition, initial attempts have been made to consider how frames might

be derived from the input in a less direct manner and then underpin children’s early linguistic

representations and their development towards the adult end-state. Here, instances of

children’s linguistic creativity require a focus on the interaction between the distributional

properties of the input and communicative function. One example is the development of

linguistic structures to express the negation of activities or events denoted by verbs. An

analysis of dense data for one 2-3-year-old child revealed his early use of a largely

ungrammatical no-Verb construction, before shifting to a not-Verb construction, then finally

settling on the more typical adult use of negated auxiliaries (can’t, don’t-Verb) to express

different functions (Cameron-Faulkner, Lieven, & Theakston, 2007). Although his early uses

were certainly not typical of patterns in the input, their origins were apparent: no was the

most frequent single word negator in the input whereas not was the most frequent form used

in multiword utterances. The late-acquired negated auxiliaries showed a function-specific

pattern of emergence (see also Drozd 1995) which related to the frequency and specificity of

the mapping between auxiliaries and functions in the input. Similar arguments have been put

forward to explain children’s use of double marked questions (e.g. Why do you don’t like

cake?), such that, in the absence of a suitable negative question frame (Don’t you…?)

children may resort to combining a well-known question frame (Do you…?) with an already

learned declarative form (You don’t like X) (Ambridge & Rowland, 2009). Thus, children

appear to make productive use of the resources that are available to them at any particular

point in development, reflecting a creative process by the child to discover and/or create

regularity in form and function.

Interim summary

English-learning children hear highly frequent multiunit strings in their input. Many of their

early utterances are based on these strings and this has been shown to have important effects

on the order and nature of developmental change in their linguistic systems. These strings

can explain why there are differences for structures that, despite having the same formal

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description, differ in whether children can produce them with or without error. They can also

explain the ways in which abstraction and schematicity build up and, in turn, account for

some instances of linguistic creativity. However, as children’s linguistic systems develop,

these strings will become interconnected in an increasing variety of ways, allowing children

to use them more or less appropriately or creatively in different situations. Developing

precise predictions for the relative balance of factors in the production and comprehension of

particular types of utterances over time will require the use of converging methods involving

corpus analysis, experiments and modelling.

Other languages

There are (at least) two important differences between English and many other languages

which could affect whether children can extract and learn from multiunit strings in the same

ways that English children can. First, English word order is much more syntactically

constrained than in many other languages. Although some languages are described as having

‘free word order’, it is almost certainly the case that this is pragmatically constrained, but this

will still give more flexibility than in English. Thus, the word order regularities that allow

children to learn multi-word strings may be less available in other languages. The second

major difference is that, relative to many languages, English has very little morphology.

Case-marking is almost totally absent except on pronouns, and person, tense and aspectual

marking on verbs is also very limited. Other languages have extensive case systems (e.g.

Estonian and Polish are usually credited with seven singular and seven plural cases) and

verbal inflections (e.g. in addition to person, number and tense, Turkish marks evidentiality

and Russian marks perfective/imperfective aspect). Thus, rich inflectional morphology may

pose different challenges for children learning these types of languages.

Word order

Looking first at the input, Stoll, Abbot-Smith, and Lieven (2009) used a method similar to

that of Cameron-Faulkner et al. (2003) to determine the evidence for low-scope frames in the

CDS of German, English, and Russian. Despite differences due to the typology of the

languages, they found a very high degree of repetition in the first 1-3 words of the mothers’

utterances, which could facilitate the early acquisition of low-scope frames (see also Arnon

2016 for Hebrew). In computational modelling work, researchers have demonstrated that

words from a variety of languages can be classified into grammatical categories (e.g.

Croatian, English, Estonian, Dutch, French, Hebrew, Hungarian, Japanese, Sesotho) using a

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combination of distributional and phonological information (Monaghan, Christiansen, &

Chater, 2007), or localised slot-and-frame patterns (Mintz, 2003, but see Stumper et al.,

2011). McCauley and Christiansen (2014) developed a chunk-based learning model and

applied it to corpora of children’s language and their input in 29 languages that differ widely

in their degree of morphological complexity. The model learns from CDS using backward

transitional probabilities and then is set the task of generating the children’s utterances by

correctly sequencing words presented in random order (see Chang, Lieven & Tomasello,

2008). The model achieves a mean accuracy rate of 78% for English child corpora. When

tested with 29 languages, the model was less accurate with morphologically complex

languages than for those with simpler morphology. However, since the model is trained on

words rather than morphemes, this suggests that there is considerable information in the

transitional probabilities between words, even in highly inflected languages.

One study that suggests that children learning languages other than English extract strings

from the input is a cross-linguistic comparison of tense omission errors (Freudenthal, Pine &

Gobet, 2010). Using a computational model which builds up chunks from the ends of

utterances in CDS, they showed that differences in the rates of tense omission in children

learning different languages could be explained by typological differences in the organisation

of finiteness marking, with some languages (English, German and Dutch) having a larger

proportion of non-finite verb forms at the ends of utterances than others (French & Spanish).

Further evidence comes from children’s use of complement-taking verbs in German. Brandt,

Lieven and Tomasello (2010) demonstrated that children start out with separate schemas for

verb-final and verb-second complements, each appearing with different groups of verbs and

different types of main clauses. Only gradually, over the third year, are these separate

constructions used more flexibly and in overlapping ways, providing evidence for children

creating structural links between them.

We have suggested that for English, pronouns act as an anchor for the learning of lexical

frames and as a basis for generalisation into more abstract constructions. The extent to which

pronouns might play a similar role in other languages will depend on whether their relative

frequency and distributional properties lend themselves to early acquisition. To illustrate,

consider a ‘weird word order’ study with French-speaking children (Matthews, Lieven,

Theakston, & Tomasello, 2007). Although English-speaking children frequently corrected

weird word orders by producing pronominal objects, in contrast, French-speaking children

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rarely did so. The likely explanation is that French word order is more variable than in

English and differs according to whether lexical or pronominal objects are produced. Object

clitic pronouns appear pre-verbally (SoV - Il la pousse), whereas lexical noun objects occur

after the verb (SVO - Il pousse Marie). Consequently, it may be more difficult for French-

speaking children to derive the form-function mappings for the transitive and, initially at

least, they may learn two more fragmented constructions, and learn these more slowly due to

the lower individual frequency of the two word orders.

Morphological patterns in other languages

Thus far, we have mainly focussed on multi-word strings as the potential building blocks for

the acquisition of more abstract syntactic constructions. For English, this works reasonably

well, and we have also demonstrated the potential utility of such an approach in other

languages. However, in many languages it is necessary to consider the initial building blocks

at an even lower level of granularity – that of morphological marking.

Languages vary greatly not only in the extent of inflectional morphology present but also in

its complexity. For instance, languages like English, Chinese and Japanese have relatively

little inflectional morphology and what there is, is relatively transparent (they are more

‘analytic’ or ‘isolating’). At the other end of the scale are ‘polysynthetic’ languages like

Chintang (a Tibet-Burman language spoken in Eastern Nepal) in which a transitive verb has

more than 1849 synthetic forms per verb (Stoll & Bickel 2013). Between these two extremes

lie ‘synthetic’ languages but these can vary greatly in their degree of transparency in

morpheme-to-function mapping. Some languages are agglutinative with a fixed sequence of

morphemes which map on a one-to-one basis with a function (e.g. Turkish). Others are

fusional (e.g. Polish in which gender, person and number are all combined in one morpheme).

Finally, some languages show a lot of homophony (e.g. German, where one form of the

determiner, die, can be feminine, singular, nominative or accusative, as well as masculine,

feminine or neuter, nominative or accusative, plural). These different types of morphological

systems will set different challenges to learning.

In determining the nature of the challenge facing the learner, it is essential to look at the

morphological complexity of the language that children hear: as Xanthos et al (2011) point

out, this could differ considerably from the full array of forms and combinations possible in

the grammar. Xanthos et al. developed a measure of the morphological richness of nouns and

13

verbs in CDS and child corpora for a variety of languages (Mean Size of Paradigm, MSP),

and demonstrated that this can be relatively low even for languages with complex

morphology (e.g. although Croatian has complex morphology, for instance 18 different verb

forms (Stephany et al 2007), the MSP in Croatian CDS was a relatively low 1.4, compared to

Turkish CDS of 1.91). Their MSP measure of CDS across 9 languages was strongly

positively related to the speed with which the children developed the noun and verb

paradigms of the language that each was learning.

It is clear that children learning highly inflected languages do not start out with a fully-

fledged system. Studies on Spanish and Polish show that when a comparison is made

between the degree of flexibility in the use of morphemes in CDS and the child’s speech,

with careful controls applied for vocabulary, available inflections, and sample size, children

are significantly less productive than their caregivers until around age 3;0 (Aguado-Orea &

Pine 2015, Krajewski, Lieven & Theakston, 2012). Furthermore, entropy measures suggest

that initially morphemes are closely tied to particular constructions and that they become less

closely associated as the child’s system develops (Krajewski, et al., 2012; Stoll & Bickel

2013), raising the possibility that children learning complex morphological systems may rely

on strings or low-scope frames. Moreover, although overall error rates in the use of inflected

forms might be low, this typically hides pockets of pronounced error in (lower frequency)

parts of the system. Aguado-Orea & Pine (2015) showed that for Spanish present tense

inflections, very high rates of error are found in some parts of the person-number paradigm.

Frequency was very strongly associated with correct use, suggesting that inflected forms may

initially be learned as ‘chunks’ from the input, (only two verbs, I want=quiero and I can=

puedo, accounted for nearly 50% of correct, 1st person usage, see also Rojas Nieto 2011).

Morphological richness is demonstrated not only through the number of distinct noun/verb

forms possible in a language, but also by the number of affixes that can be present in a word.

Here, however, it is important to consider the degree of systematicity in the ways in which

these forms are combined. Kelly, Wigglesworth, Nordlinger and Blythe suggest that

“Polysynthetic languages contain words with many morphemes and expressing complex

grammatical concepts, but may be relatively regular in the templatic sequence in which they

are used.” (2014: 61). Although they express doubt about the usefulness of chunk learning in

these types of languages, if children are learning these templates as partially productive

strings, with some slots becoming schematic before others, this could provide a way into the

14

structure. In a study of Turkish newspaper articles (presumably with more complex language

that that addressed to children), Durrant (2013) identified ‘morpheme bundles’, sometimes

fully specified, other times containing partially productive slots; combinations that appeared

frequently, and which speakers could represent as highly accessible strings, suggesting that a

language like Turkish might lend itself to templatic slot-and-frame-based learning. Indeed,

Aksu-Koç and Slobin (1985: 206) suggested that Turkish children sometimes use schwas as

placeholders i.e. having learned the kind of templatic sequence that it seems Kelly et al. are

referring to, they were aware that a morpheme was required but did not know what it was.

We have conceptualised morphological slot-and-frame patterns as developing out of fixed

elements such as particular stems or morphemes which combine with a variety of items (e.g.

words denoting actions, morphemes denoting different person/number combinations or

tenses). If one thinks of inflectional morphology as showing regularities both ‘vertically’

(declensions, conjugations) and ‘horizontally’ (cases, person marking), there is evidence that

children can show partial productivity on both fronts. Thus, Dąbrowska and Tomasello

(2008) documented Polish children’s ability to abstract a particular case and generalise it to

other novel nouns (‘horizontal’ generalisation), while Krajewski, Theakston, Lieven and

Tomasello (2011) showed that children’s ability to provide the correct inflection for a

particular noun varies as a function of the previous case in which they heard it (‘vertical’

generalisation). However, this process may be complex in languages in which inflections

encode more than one function (e.g. a combination of both case and person as in Polish).

Furthermore, in many languages, there is no base form or stem, and thus the challenge facing

the child is not simply one of removing and replacing morphemes, but of learning relations

between distinct inflected forms.

All this suggests that the learning of phonologically-specific, inflected words, followed by the

development of low-scope, slot-and-frame patterns might be important processes in the early

learning of inflectional morphology. But the truth is that research from this perspective is

only just getting off the ground, and there are many challenges to be addressed in

understanding the extent to which these processes operate as we consider languages with a

wide range of typological characteristics and complexities.

Remaining issues

15

Although there has been considerable work on the role of multiunit strings in children’s

acquisition of English and to a lesser extent in other languages, in terms of forming the basis

for longer utterances, and underpinning grammatical errors and correct use, the question of

how these strings facilitate the process of abstraction has been less closely explored. And yet

understanding the process of abstraction is critical to developing a full theory of language

acquisition. In constructivist or usage-based approaches to adult language, it is widely

acknowledged that linguistic representations exist at multiple levels, from the fully

phonologically specified through to partially productive and fully abstract forms (Goldberg

2006, Verhagen 2005). Thus, in acquisition, children starting out with less abstract forms will

simultaneously begin to develop more abstract representations while retaining at least some

of the earlier learned forms.

As this process gets underway, we might expect to find some interesting patterns of results,

depending on whether children are utilising more abstract or more specific representations.

Indeed, some work with adults suggests that multiunit strings may differentially influence

speakers’ production and comprehension of high vs. low frequency exemplars, with low

frequency items more influenced by the global statistics of the input, whereas higher

frequency items retain item-specific patterns of use (Wonnacott, Newport, & Tanenhaus,

2008, see Dittmar, Abbot-Smith, Lieven, & Tomasello, 2013 for similar work on children’s

interpretation of passive sentences with familiar and novel verbs). Thus, learners apparently

keep track of specific linguistic information whilst simultaneously deriving the broad

statistics of the language. The extent to which either the broad or local statistics influence

subsequent behaviour is dependent on the strength of association between specific items and

the material with which they co-occur, and this will change over the course of development.

Another influence on the process of abstraction is construction meaning, and its interaction

with the meanings of particular lexical items. For example, Ambridge and colleagues

(Ambridge, Pine & Rowland, 2012) have demonstrated that the likelihood of adults and

children judging argument structure errors as grammatical (e.g. *He disappeared the rabbit)

depends on the extent to which the verb meaning is deemed compatible with the meaning of

the construction. This means that to understand how multiunit strings are broken down and

recombined in the language learner, we will need models of acquisition that are sensitive to

the meanings of the strings, and the semantic scope of the resulting slots. There is already an

assumption that the slots in constructions are semantically restricted, as reflected in the

16

choice of terminology (e.g. I PROCESS THING; Lieven et al., 2009), and there is some

evidence that slot-and-frame patterns in CDS may have particular functions (Cameron-

Faulkner & Hickey, 2011). However, to date there is relatively little work which explores this

issue directly (although see Matthews & Bannard, 2010).

Conclusions

In summary, multiunit strings provide one useful basis from which to learn language, but

while we have begun to understand their utility in the earliest stages of acquisition, there is a

long way to go before we can hope to fully understand how these mechanisms change over

time, how both multiunit strings and grammatical abstractions can co-exist into adult

language, and how these processes differ across languages as a function of their typological

make up. Critically, though, different cues are going to be used to a greater or lesser extent in

different languages, and with variable success depending on the kind of distributional

information that is available. Thus, only a learning mechanism that can pick up a variety of

cues and weigh them appropriately as a function of the language being learned will be

successful in explaining how and when multiunit strings will be learned from the input, what

the units consist of and how they might develop in terms of abstraction across different

languages.

17

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