Psycholinguistics/Development of Speech Production
- 1 Introduction
- 2 Prelinguistic Speech Development
- 3 Phonological Development
- 4 Semantic Development
- 5 Grammatical and Morphological Development
- 6 Summary
- 7 Learning Exercise
- 8 Learning Exercise Answers
- 9 References
Speech production is an important part of the way we communicate. We indicate intonation through stress and pitch while communicating our thoughts, ideas, requests or demands, and while maintaining grammatically correct sentences. However, we rarely consider how this ability develops. We know infants often begin producing one-word utterances, such as "mama," eventually move to two-word utterances, such as "gimme toy" and finally sound like an adult. However, the process itself involves development not only of the vocal sounds (phonology), but also semantics (meaning of words), morphology and syntax (rules and structure). How do children learn to this complex ability? Considering that an infant goes from an inability to speak to two-word utterances within 2 years, the accelerated development pattern is incredible and deserves some attention. When we ponder children's speech production development more closely, we begin to ask more questions. How does a child who says "tree" for "three" eventually learn to correct him/herself? How does a child know "nana" (banana) is the yellow,boat-shaped fruit he/she enjoys eating? Why does a child call all four-legged animals "horsie"? Why does this child say "I goed to the kitchen"? What causes a child to learn words such as "doggie" before "hand"? This chapter will address these questions and focus on the four areas of speech development mentioned: phonology, semantics, and morphology and syntax.
Prelinguistic Speech Development
Throughout infancy, vocalizations develop from automatic, reflexive vocalizations with no linguistic meaning to articulated words with meaning and intonation. In this section, we will examine the various stages an infant goes through while developing speech. In general, researchers seem to agree that as infants develop they increase their speech-like vocalizations and decrease their non-speech vocalizations (Nathani, Ertmer, & Stark). Many researchers (Oller, ; Stark, as cited in Nathani, Ertmer, & Stark, 2006). Many researchers (Oller; Stark, as cited in Nathani, Ertmer, & Stark,) have documented this development and suggest growth through the following five stages: reflexive vocalizations, cooing and laughing, vocal play (expansion stage) , canonical babbling and finally, the integration stage.
Stage 1: Reflexive Vocalization
As newborns, infants make noises in responses to their environment and current needs. These reflexive vocalizations may consist of crying or vegetative sounds such as grunting, burping, sneezing, and coughing (Oller). Although it is often thought that infants of this age do not show evidence of linguistic abilities, a recent study has found that newborns’ cries follow the melody of their surrounding language input (Mampe, Friederici, Christophe, & Wermke). They discovered that the French newborns’ pattern was a rising contour, where the melody of the cry rose slowly and then quickly decreased. In comparison, the German newborns’ cry pattern rose quickly and slowly decreased. These patterns matched the intonation patterns that are found in each of the respective spoken languages. Their finding suggest that perhaps infants vocalizations are not exclusively reflexive and may contain patterns of their native language.
Stage 2: Gooing, Cooing and Laughing
Between 2 and 4 months, infants begin to produce “cooing” and “gooing” to demonstrate their comfort states. These sounds may often take the form of vowel-like sounds such as “aah” or “oooh.” This stage is often associated with a happy infant as laughing and giggling begin and crying is reduced. Infants will also engage in more face-to-face interactions with their caregivers, smiling and attempting to make eye contact (Oller).
Stage 3: Vocal Play
From 4 to 6 months, and infants will attempt to vary the sounds they can produce using their developing vocal apparatus. They show a desire to explore and develop new sounds which may include yells, squeals, growls and whispers(Oller). Face-to-face interactions are still important at this stage as it promotes development of conversation abililities. Beebe, Alson, Jaffe et al.found that even at this young age, infants’ vocal expression show a “dialogic structure” - meaning that, during interactions with caregivers, infants were able to take turns vocalizing.
Stage 4: Canonical babbling
After 6 months, infants begin to make and combine sounds that are found in their native language, sometimes known as “well-formed syllables,” which are often replicated in their first words(Oller). During this stage, infants combine consonants and vowels and replicate them over and over - they are thus called reduplicated babble. For example, an infant may produce ‘ga-ga’ over and over. Eventually, infants will begin to string together multiple varied syllables, such as ‘gabamaga’, called variegated babbles. Other times, infants will move right into the variegated babbles stage without evidence of the reduplicated babbles (Oller). Early in this stage, infants do not produce these sounds for communicative purposes. As they move closer to pronouncing their first words, they may begin to use use sounds for rudimentary communicative purposes(Oller).
Stage 5: Integration
In the final stage of prelinguistic speech, 10 month-old infants use intonation and stress patterns in their babbling syllables, imitating adult-like speech. This stage is sometimes known as conversational babble or gibberish because infants may also use gestures and eye movements which resemble conversations(Oller). Interestingly, they also seem to have acoustic differences in their vocalizations depending on the purpose of their communication. Papaeliou and Trevarthen  found that when they were communicating for social purposes they used a higher pitch and were more expressive in their vocalizations and gestures than when exploring and investigating their surroundings. The transition from gibberish to real words is not obvious(Oller) as this stage often overlaps with the acquisition of an infant’s first words. These words begin when an infant understands that the sounds produced are associated with an object .During this stage, infants develop vocal motor schemes, the consistent production of certain consonants in a certain period of time. Keren-Portnoy and Marjorano’s study showed that these vocal motor schemes play a significant part in the development of first words as children who children who mastered them earlier, produced words earlier. These consistent consonants were used in babble and vocal motor schemes, and would also be present in a child’s first words. Evidence that a child may understand the connection between context and sounds is shown when they make consistent sound patterns in certain contexts (Oller). For example, a child may begin to call his favorite toy “mub.” These phonetically-consistent sound patterns, known as protowords or quasi-words, do not always reflect real words, but they are an important step towards achieving adult-like speech(Otomo; Oller). Infants may also use their proto-words to represent an entire sentence (Vetter). For example, the child may say “mub” but may be expressing “I want my toy”, “Give me back my toy” “Where is my toy?”, etc.
When a child explicitly pronounces their first word they have understood the association between sounds and their meaning Yet, their pronunciation may be poor, they produce phonetic errors, and have yet to produce all the sound combinations in their language. Researchers have come up with many theories about the patterns and rules children and infants use while developing their language. In this section, we will examine some frequent error patterns and basic rules children use to articulate words. We will also look how phonological development can be enhanced.
Patterns of Speech
Depending on their personalities and individual development, infants develop their speech production slightly differently. Some children,productive learners, attempt any word regardless of proper pronunciation (Rabagaliati, Marcus, & Pylkkänen) . Conservative learners (Rabagaliati, Marcus, & Pylkkänen), are hesitant until they are confident in their pronunciation. Other differences include preference to use nouns and name things versus use of language in a more social context. (Bates et al., as cited in Smits-Bandstra). Although infants vary in their first words and the development of their phonology, by examining the sound patterns found in their early language, researchers have extracted many similar patterns. For example, McIntosh and Dodd examined these patterns in 2 year olds and found that they were able to produce multiple phonemes but were lacking [ʃ,θ,tʃ,dʒ,r]. They were also able to produce complex syllables. Vowel errors also occurred, although consonant errors are much more prevalent. The development of phonemes continues throughout childhood and many are not completely developed until age 8 (Vetter).
As a child pronounces new words and phonemes, he/she may produce various errors that follow patterns. However, all errors will reduce with age (McIntosh & Dodd). Although each child does not necessarily produce the same errors, errors can typically be categorized into various groups. For example, they are multiple kinds of consonant errors. A cluster reduction involves reducing a multiple consonants in a row (ie: skate). Most often, a child will skip the first consonant (thus skate becomes kate), or they may leave out the second stop consonant (consonant deletion - Wyllie-Smith, McLeod, & Ball) (thus skate becomes sate). This type of error has been found by McIntosh and Dodd . For words that have multiple syllables, a child may skip the unstressed syllable at the beginning of the sentence (ie: potato becomes tato) or in the middle of a sentence (ie: telephone becomes tephone) (Ganger & Brent). This omission may simply be due to the properties of unstressed syllables as they are more difficult to perceive and thus a child may simply lack attention to it. As a child grows more aware of the unstressed syllable, he/she may chose to insert a dummy syllable in place of the unstressed syllable to attempt to lengthen the utterance (Aoyama, Peters, & Winchester). For example, a child may say [ə hat] (‘ə hot’) (Clark, as cited in Smits-Bandstra). Replacement shows that the child understands that there should be some sound there, but the child has inserted the wrong one. Another common phonological error pattern is assimilation. A child may pronounce a word such that a phoneme within that word sounds more like another phoneme near it (McIntosh & Dodd). For example, a child may say “”gug” instead of “bug”. This kind of error may also be seen for with vowels and is common in 2 year-olds, but decreases with age (Newton).
Definition of Error Patterns
Factors affecting development of phonology
As adequate phonology is an important aspect in effective communication, researchers are interested in factors that can enhance it. In a study done by Goldstein and Schwade, it was found that interactions with caregivers provided opportunities for8-10 month old infants to increase their babbling of language sounds (consonant-vowel syllables and vowels). This study also found that infants were not simply imitations their caregivers vocalizations as they were producing various phonological patterns and had longer vocalizations! Thus, it would seem that social feedback from caregivers advances infants phonological development. On the other hand, factors such as hearing impairment, can negatively affect phonological development (Nicolaidis ). A Greek population with hearing impairments was compared to a control group and it was found that they have a different pattern of pronunciation of phonemes. Their pattern displayed substitutions (ie:[x] for target /k/), distortions (ie: place of articulation)and epenthesis/cluster production (ie:[ʃtʃ] or [jθ] for /s/) of words.
When children purposefully use words they are trying to express a desire, refusal, a label or for social communication (Ninio & Snow ). As a child begins to understand that each word has a specific purpose, they will inevitably need to learn meaning of multiple words. Their vocabulary will rapidly expand as they experience various social contexts, sing songs, practice routines and through direct instruction at school (Smits-Bandstra, 2006). In this section, we will examine children’s first words, their vocabulary spurt, and what their semantic errors are like.
Many studies have analyzed the types of words found in early speech. Overall, children’s first words are usually shorter in syllabic length, easier to pronounce, and occur frequently in everyday speech (Storkel, 2004). Whether early vocabularies have a noun-bias or not tends to divide researchers. Some researchers argue that the noun bias, or children’s tendency to produce names for objects, people and animals, is sufficient evidence of this bias (Gllette et al.) . However, this bias may not be entirely accurate. Recently, Tardif  studied first words cross-culturally between English, Cantonese and Mandarin 8-16 month old infants and found interesting differences. Although all children used terms for people, there was much variation between languages for animals and objects. This suggests that there may be some language differences in which types of words children acquire first.
Around the age of 18 months, many infants will undergo a vocabulary spurt, or vocabulary explosion, where they learn new words at an increasingly rapid rate (Smits-Bandstra); Mitchell & McMurray,2009. Before onset of this spurt, the first 50 words a child learned as usually acquired at a gradual rate (Plunkett, as cited in Smits-Bandstra).Afterward the spurt, some studies have found upwards of 20 words learned per week( Mitchell and McMurray). There has been a lot of speculation about the process underlying the vocabulary spurt and there are three main theories. First, it has been suggested that the vocabulary spurt results from the naming insight (Reznick and Gldfield). The naming insight is a process where children begin to understand that referents can be labeled, either out of context or in place of the object. Second, this period seems to coincide with Piaget’s sensorimotor stage in which children are expanding their understanding of categorizing concepts and objects. Thus, children would necessarily need to expand their vocabulary to label categories (Gopnik). Finally, it has been suggested that leveraged learning may facilitate the vocabulary explosion (Mitchell & McMurray) . Learning any word begins slowly - one word is learned, which acts as a ‘leverage’ to learn the next word, then those two words can each facilitates learning a new word, and so on. Learning therefore becomes easier. It is possible that not all children experience a vocabulary spurt, however. Some researchers have tested to determine whether there truly is an accelerated learning process. Interestingly, Ganger and Brent  used a mathematical model and found that only a minority of the infants studied fit the criteria of a growth spurt. Thus the growth spurt may not be as common as once believed.
Even after a child has developed a large vocabulary; errors are made in selecting words to convey the desired meaning. One type of improper word selection is when children invent a word (called lexical innovation). This is usually because they have not yet learned a word associated with the meaning they are trying to express, or they simply cannot retrieve it properly. Although made-up words are not real words, it is fairly easy to figure out what a child means, and sometimes easier to remember than the traditional words (Clarke, as cited in Swan). For example, a child may say “pourer” for “cup” (Clarke, as cited in Swan).These lexical innovations show that the child is able to understand derivational morphology and use it creatively and productively (Swan).
Sometimes children may use a word in an inappropriate context either extending or restricting use of the word. For example, a child says “doggie” while pointing to any four-legged animal - this is known as overextension and is most common in 1-2 year olds (McGregor, et al.  Bloomquist; Bowerman; Jerger & Damian). Other times, children may use a word only in one specific context, this is called underextension (McGregor, et al.  Bloomquist; Bowerman; Jerger & Damian). For example, they may only say “baba” for their bottle and not another infant’s bottle. Semantic errors manifest themselves in naming tasks and provide an opportunity to examine how children might organize semantic representations. In McGregor et al.’s naming pictures task for 3-5 year olds, errors were most often related to functional or physical properties (ie: saying chair for saddle). Why are such errors produced? McGregor et al. proposed three reasons for these errors:
- 1. they are attempting to fill the lexical gap because they do not have a current label for that particular item.
- 2. They don’t know the target word sufficiently and thus have difficulty determining which label the target should receive.
- 3. They temporarily cannot retrieve the word.
Grammatical and Morphological Development
As children develop larger lexicons, they begin to combine words into sentences that become progressively long and complex, demonstrating their syntactic development. Longer utterances provide evidence that children are reaching an important milestone in beginning the development of morphosyntax (Aoyama et al.) . Brown developed a method that would measure syntactic growth called mean length of the utterance (MLU). It is determined by recording or listening to a 30-minute sample of a child’s speech, counting the number of meaningful morphemes (semantic roles – see chart below) and dividing it by the number of utterances. Meaningful morphemes can be function words (ie: “of” ), content words (ie: “cat”) or grammatical inflections (ie: -s). Utterances will include each separate thought conveyed thus repetitions, filler words, recitations, or titles and compound words would be counted as one utterance. Brown ended up with 5 different stages to describe syntactical development: Stage I (MLU 1.0-2.0), Stage II (MLU 2.0-2.5), Stage III (MLU 2.5-3.0), Stage IV (MLU 3.0-3.5) Stage V (MLU 3.5-4.0).
|Stage||Stage I||Stage II||Stage III||Stage IV||Stage V|
What is this child's MLU?
Sample of speech: # of utterances: # of morphemes: MLU: “Mommy, want cookie. No dinner! Drink juice.”
1- Mommy want cookie.
2- No dinner
3- Drink juice
Around the age of 18 months, children’s utterances are usually in two-word forms such as “want that, mommy do, doll fall, etc.” (Vetter. In English, these forms are dominated by content words such as nouns, verbs and adjectives and are restricted to concepts that the child is learning based on their sensorimotor stage as suggested by Piaget (Brown). Thus, they will express relations between objects, actions and people. This type of speech is called telegraphic speech. During this development stage, children are combining words to convey various meanings. They are also displaying evidence of grammatical structure with consistent word orders and inflections.(Behrens & Gut; Vetter).
Once the child moves from Stage 1, simple sentences begin to form and the child begins to use inflections and function words (Aoyama et al.). At this time, the child develops grammatical morphemes (Brown) which are classified into 14 different categories organized by acquisition (See chart below).These morphemes modify the meaning of the utterance such as tense, plurality, possession, etc. There are two theories for why this particular order takes place. The frequency hypothesis suggests that children acquire the morphemes they hear most frequently in adult speech. Brown argued against this theory by analyzing adult speech where articles were the most common word form, yet children did not acquire articles quickly. He suggested that linguistic complexity may account for the order of acquisition where the less complex morphemes were acquired first. Complexity of the morphemes was determined based on semantics (meaning) and/or syntax (rules) of the morpheme. In other words, a morpheme with only one meaning such as plurality (-s) is easier to learn than the copula “is” (which encodes number and time the action occurs). Brown also suggested that for a child to have successfully mastered a grammatical morpheme, they must use it properly 90% of the time.
Order Morpheme Example 1 Present progressive (-ing) running 2-3 in, on sit on chair 4 Plural (-s) cookies 5 Past irregular ran,drew 6 Possessive (-'s) Daddy's toy 7 Uncontractible copula (is) That is my cookie. 8 Articles (the, a) The cat ; "a" dog 9 Past regular (-ed) jumped 10 Third person regular he cooks 11 Third person irregular he has my toy 12 Uncontractible auxiliary (was, do) do you have one? 13 Contractible copula (-'m, are You are here 14 Contractible auxiliary (-s) He's coming!
As children begin to develop more complex sentences, they must learn to use to grammar rules appropriately too. This is difficult in English because of the prevalence of irregular rules. For example, a child may say, “I buyed my toy from the store.” This is known as an overregularization error. The child has understood that there are syntactic patterns and rules to follow, but overuses them, failing to realize that there are exceptions to rules. In the previous example, the child applied a regular part tense rule (-ed) to an irregular verb. Why do these errors occur? It may be that the child does not have a complete understanding of the word meaning and thus incorrectly selects it (Pinker, et al.). Brooks et al. suggested that these errors may be categorization errors. For example, intransitive or transitive verbs appear in different contexts and thus the child is required to learn that certain verbs appear only in certain contextes. (Brooks). Interestingly, Hartshorne and Ullman found a gender difference for overregularization errors. Girls were more than three times more likely than boys to produce overregularizations. They concluded that girls were more likely to overgeneralize associatively, whereas boys overgeneralized only through rule-governed methods. In other words, girls, who remember regular forms, better than boys, quickly associated their rule forms to similar sounding words (ie: fold-folded, mold-molded, but they would say hold becomes holded). Boys, on the other hand, will use the regular rule when they have difficulty retrieving the irregular form (ie: past tense form - ed added to irregular form run becomes runed) (Hartshorne & Ullman).
Another common error committed by children is omission of words from an utterance. These errors are especially prevalent in their early speech production, which frequently lack function words (Gerken, Landau, & Remez). For example, a child may say “dog eat bone” forgetting function words “the” and “a”.This type of error has been frequently studied and researchers have proposed three main theories to account for omissions. First, it may be that children may focus on words that have referents (Brown). For example, a child may focus on “car” or “ball”, rather than “jump” or “happy.” The second theory suggests children simply recognize the content words which have greater stress and emphasis (Brown). The final theory, suggested by Gerken, involves an immature production system. In their study, children could perceive function words and classify them into various syntactic categories, yet still omitted them from their speech production.
In this chapter, the development of speech production was examined in the areas of prelinguistics, phonology, semantics, syntax and morphology. As an infant develops, their vocalizations will undergo a transition from reflexive vocalizations to speech-like sounds and finally words. However, their linguistic development does not end there. Infants underdeveloped speech apparatus restricts them from producing all phonemes properly and thus they produce errors such as consonant cluster reduction, omissions of syllables and assimilation. At 18 months, many children seem to undergo a vocabulary spurt. Even with a larger vocabulary, children may also overextend (calling a horse a doggie) or underextend (not calling the neighbors’ dog, doggie) their words. When a child begins to combine words, they are developing syntax and morphology. Syntactic development is measured using mean length of the utterance (MLU) which is categorized into 5 stages (Brown). After stage II, children begin to use grammatical morphemes (ie: -ed, -s, is) which encode tense, plurality, etc. As with other areas of linguistic development, children also produce errors such as overregularization (ie: “I buyed it”) or omissions (ie: “dog eat bone”). In spite of children’s early errors patterns, children will eventually develop adult-like speech with few errors. Understanding and studying child language development is an important area of research as it may give us insight into underlying processes of language as well as how we might be able to facilitate it or treat individuals with language difficulties.
1. Watch the video clips of a young boy CC provided below.
- (a)For each clip, indicate at which stage of prelinguistic development (Stage 1 -5) CC is and how you arrived at this conclusion.
- (b) An infant says "lalu" whenever she is given her bottle or wants her bottle. What is this called and during which stage of prelinguistic development does it occur?
2. The following is a transcription of conversations between a mother (*MOT) and a child (*CHI) from Brown's (1970) corpus. You can ignore the # symbol as it represents unintelligible utterances. Use the charts found in the section on "Grammatical and Morphological Development" to help answer this question.
- (a) Find 4 examples of different semantic roles used by the child and identify the type of semantic role.
- example: 'Mommy telephone' - agent + object
- example: 'Mommy telephone' - agent + object
- (b) Find examples that would suggest that the child is not yet producing the following grammatical morphemes:
- Possessive morphemes ('s)
- in, on
- Present progressive (-ing)
- (*hint: Compare the mother's repetition to the child's utterance or the child's repetition to the mother's utterance.Do they match?)
- (c) Based on this data sample, does this child appear to have mastered the grammatical morpheme category of articles (the, a)? Why or not why?
- MOT: let me see .
- MOT: over here +...
- MOT: you have tapioca on your finger .
- CHI: tapioca finger .
- MOT: here you go .
- CHI: more cookie .
- MOT: you have another cookie right on the table .
- CHI: Mommy fix .
- MOT: want me to fix it ?
- MOT: alright .
- MOT: bring it here .
- CHI: bring it .
- CHI: bring it .
- MOT: bring it here .
- CHI: that Kathy .
- CHI: that Kathy .
- MOT: yes # that's Kathy .
- CHI: op(en) .
- CHI: op(en) .
- MOT: no # we'll leave the door shut .
- CHI: why ?
- MOT: because I want it shut .
- CHI: Mommy .
- MOT: I'll fix it once more and that's all .
- CHI: Mommy telephone .
- MOT: well # go and get your telephone .
- MOT: yes # he gave you your telephone .
- MOT: who are you calling # Eve ?
- CHI: my telephone .
- CHI: Kathy cry .
- MOT: yes # Kathy was crying .
- MOT: Kathy was unhappy .
- MOT: what is that ?
- CHI: letter .
- MOT: Eve's letter .
- CHI: Mommy letter .
- MOT: there's Mommy's letter .
- CHI: Eve letter .
- MOT: what is that ?
- CHI: a fly .
- MOT: yes # a fly .
- MOT: why don't you go in the room and kill a fly ?
- MOT: you go in the room and kill a fly .
- CHI: fly .
- MOT: yes # you get a fly .
- MOT: oh # what's that ?
- CHI: hat .
- MOT: I'm going to go in the basement # Eve .
3. Below are examples of children's speech. These children are displaying some characteristics of terms of we have covered in this chapter. The specfic terms found in each video are provided. Find examples of these terms within their associated video. Indicate which type of development (phonological, semantic, syntactic) is associated with each of these term.
|Dummy Syllable||Video 1|
|Lexical Innovations||Video 2|
What kind of learner (conservative or productive)?
|This child does not produce which two phonemes?
** hint, "camera" and "the"
|Cluster reduction||video 5|
- (a) 24 month old Alex has learned that objects have names. He labels most things or asks "what that?". He is also speaking consistently in telegraphic speech (two-word utterances). It would seem that Alex has undergone which developmental milestone? Explain the theories on how this developmental milestone is reached.
- (b) Some of Alex's first words were “birdy, milk, mama, sissy, ball, doggie”. This shows evidence of which bias?
- (c) Alex uses "birdy" when referring to the family pet parakeet, but also when he sees butterflies, airplanes, or kites. What is his error?
5.The following are examples of children’s speech errors. Name the error and the type of development it is associated with (phonological, syntactic, morphological, or semantic). Can you explain why such an error occurs?
- (a) juice holder (cup)
- (b) apple (while eating an orange)
- (c) he “goed” away
- (d) sool (for school)
- (e) limiting “kitty” to child’s pet cat
- (f) ephant (elephant)
- (g) kuk (buck)
- (h) “want shoe” (I want the shoe) or “plate green” (the plate is green)
Learning Exercise Answers
- Nathani, S., Ertmer, D. J., & Stark, R. E. (2006). Assessing vocal development in infants and toddlers. Clinical linguistics & phonetics, 20(5), 351-69.
- Oller, D.K.,(2000). The Emergence of the Speech Capacity. NJ: Lawrence Erlbaum Associates, Inc.
- Mampe, B., Friederici, A. D., Christophe, A., & Wermke, K. (2009). Newbornsʼ cry melody is shaped by their native language. Current biology : CB, 19(23), 1994-7.
- Beebe, B., Alson, D., Jaffe, J., Feldstein, S., & Crown, C. (1988). Vocal congruence in mother-infant play. Journal of psycholinguistic research, 17(3), 245-59.
- Papaeliou, C. F., & Trevarthen, C. (2006). Prelinguistic pitch patterns expressing “communication” and “apprehension.” Journal of Child Language, 33(01), 163.
- Keren-Portnoy, T., Majorano, M., & Vihman, M. M. (2009). From phonetics to phonology: the emergence of first words in Italian. Journal of child language, 36(2), 235-67.
- Otomo, K. (2001). Maternal responses to word approximations in Japanese childrenʼs transition to language. Journal of Child Language, 28(1), 29-57.
- Vetter, H. J. (1971). Theories of Language Acquisition. Journal of Psycholinguistic Research, 1(1), 31. McIntosh, B., & Dodd, B. J. (2008). Two-year-oldsʼ phonological acquisition: Normative data. International journal of speech-language pathology, 10(6), 460-9. Cite error: Invalid
<ref>tag; name "vet" defined multiple times with different content
- Rabagliati, H., Marcus, G. F., & Pylkkänen, L. (2010). Shifting senses in lexical semantic development. Cognition, 117(1), 17-37. Elsevier B.V.
- Smits-bandstra, S. (2006). The Role of Segmentation in Lexical Acquisition in Children Rôle de la Segmentation Dans l’Acquisition du Lexique chez les Enfants. Audiology, 30(3), 182-191.
- McIntosh, B., & Dodd, B. J. (2008). Two-year-oldsʼ phonological acquisition: Normative data. International journal of speech-language pathology, 10(6), 460-9.
- Wyllie-Smith, L., McLeod, S., & Ball, M. J. (2006). Typically developing and speech-impaired childrenʼs adherence to the sonority hypothesis. Clinical linguistics & phonetics, 20(4), 271-91.
- Ganger, J., & Brent, M. R. (2004). Reexamining the vocabulary spurt. Developmental psychology, 40(4), 621-32.
- Aoyama, K., Peters, A. M., & Winchester, K. S. (2010). Phonological changes during the transition from one-word to productive word combination. Journal of child language, 37(1), 145-57.
- Newton, C., & Wells, B. (2002, July). Between-word junctures in early multi-word speech. Journal of Child Language.
- Goldstein, M. H., & Schwade, J. a. (2008). Social feedback to infantsʼ babbling facilitates rapid phonological learning. Psychological science : a journal of the American Psychological Society / APS, 19(5), 515-23. doi: 10.1111/j.1467-9280.2008.02117.x.
- Nicolaidis, K. (2004). Articulatory variability during consonant production by Greek speakers with hearing impairment: an electropalatographic study. Clinical linguistics & phonetics, 18(6-8), 419-32.
- Nionio, A., & Snow, C. (1996). Pragmatic development. Boulder, CO: Westview Press
- Smits-bandstra, S. (2006). The Role of Segmentation in Lexical Acquisition in Children Rôle de la Segmentation Dans l’Acquisition du Lexique chez les Enfants. Audiology, 30(3), 182-191.
- Storkel, H. L. (2004). Do children acquire dense neighborhoods? An investigation of similarity neighborhoods in lexical acquisition. Applied Psycholinguistics, 25(02), 201-221.
- Gillette, J., Gleitman, H., Gleitman, L., & Lederer, a. (1999). Human simulations of vocabulary learning. Cognition, 73(2), 135-76.
- Tardif, T., Fletcher, P., Liang, W., Zhang, Z., Kaciroti, N., & Marchman, V. a. (2008). Babyʼs first 10 words. Developmental psychology, 44(4), 929-38.
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