1. Chapter 6 The Trajectory Towards Mastery of the Phonological System: From Toddlers to School-Aged Children
Andrea MacLeod

2. Introduction
To identify a speech sound delay or disorder in a given individual, speech-language pathologists need to understand the developmental trajectory
This chapter reviewed 31 studies selected by the following criteria:
Age range: 2 to 13 years
Typical development
Monolingual English
Publication in scientific journals, written in English
Studies were based on data from children in Australia, Canada, New Zealand, and the United States of America
Criteria of interest
Accuracy
Inventory
Error patterns

3. Toolkit for Measuring Accuracy
You start with a conversational sample (recommended size: at least 25 utterances but 100 is better), transcribe it, and calculate the following:
Percent Consonants Correct (PCC): the number of correctly produced consonants, divided by all consonants produced, multiplied by 100 (errors must be substitutions or omissions)
Percent Vowels Correct (PVC): the number of correctly produced vowels, divided by all vowels produced, multiplied by 100
Percent Phonemes Correct (PPC): the number of correctly produced phonemes, divided by all phonemes produced, multiplied by 100
Articulation Competency Index (ACI): the number of correctly produced consonants, divided by all consonants produced, multiplied by 100 (errors can be distortions, e.g., [l] or [d] that is fronted. Similar to PCC but errors can include distortions -> useful for assessing older children and adults

4. Intelligibility Index: Percent of words judged to be intelligible by a trained transcriber
Phonological Mean Length of Utterance (PMLU): a measure of the number of phonemes in the produced word plus the number of accurately produced consonants
Example: [næna]/banana: = 6
The score from all the words in the sample are then averaged
A child who mostly produces short words accurately will have a similar PMLU as a child who attempts longer words but omits sounds
Whole Word Proximity (WWP): a measure of the child’s PMLU as a proportion of the target PMLU
Example: [wi]/week: PMLU child = 3;PMLU target [wik]: = 5
WWP 3/5 = .6
A child who mostly produces short words accurately will have a higher WWP compared to a child who attempts longer words but truncates them. Therefore, the child’s and the target PMLU should be considered separately as well as a ratio.
Proportion Whole-Words Correct (PWC): a measure of how many words in a sample were completely correct

5. Sound Inventory for One Child
Start with a conversational speech sample or single-word productions from an articulation test and transcribe what the child said
Independent analysis results in a phonetic inventory (other terms: segmental inventory, absolute inventory)
Simply make a list of all the phonemes you heard – can group them by place, manner, voicing
Relational analysis results in a phonemic inventory (other term: relational inventory)
Compare the the child’s productions to the adult form and count only those sounds as correct that are correct relative to the adult form
Example:
[θʌn]/sun
[fʌm]/thumb
[fud]/food
Independent analysis: / d, θ, f, m, n, ʌ, u/ (just the sounds you heard)
Relational analysis: / d, f, m, n, ʌ, u/ but /s, θ/ are missing. Why???

6. Sound Inventory for a Group of Children
At what age do children typically acquire a certain sound or sound class?
Another way of asking: What proportion of same-age children should produce the sound or sound class correctly for it to be considered “acquired”? Studies vary:
75% of the children
90% of the children

7. Phonotactic Inventories
May include all words in the sample or only those whose syllable and word shapes match the adult target
Word shapes: “Me want cookie”:
X (monosyllabic word), Xx (disyllabic word, strong + weak syllable)
Syllable shapes: “Me want cookie”
CV, CVCC, CVCV

8. Error Patterns (Phonological Processes)
Assimilation processes: sound changes that achieve greater similarity to neighboring sounds
Can occur by anticipation (right to left) or perseveration (left to right)
Place:
Labial [bɔb]/ball
Velar [kek]/take
Alveolar [tet]/take
Nasal [mun]/moose
Voicing
Prevocalic voicing [baɪ]/pie
Postvocalic devoicing [pɪk]/pig
Prevocalic devoicing [pʊk]/book
Postvocalic voicing [bʊg]/book

9. Word or syllable structure processes
Weak syllable deletion [nænǝ]/banana
Cluster reduction [kul]/school
Final consonant deletion [bʊ]/book
Initial consonant deletion [ʊk]/book
Coalescence [tet]/skate
Epenthesis [bəlu]/blue
Doubling [dɔdɔ]/dog
Reduplication [wawa]/water (this is also considered an assimilation process, syllable harmony)
Glottal replacement [ʔʊʔi]/cookie
Metathesis [æmɪnəl]/animal
Migration [pæsgɛdi]/spaghetti

10. Substitution processes, e.g.,
Gliding [wɪŋ]/ring, [jaɪt]/light
Stopping [tʌn]/sun
Fronting [ti]/key (velar), [si]/she (palatal)
Backing [gɔg]/dog (note: this could also be assimilation!)
Depalatization [si]/she] (same as palatal fronting)
Palatization [ʃʌn]/sun
Affrication [tsʌn]/sun
Deaffrication [ʃiz]/cheeze, [tiz]/cheese (some consider the second case as stopping)
Vowelization (also called vocalization) [bado]bottle
Denasalization [bud]/moon
Neutralization (replacing multiple consonants with the same sound, often [d] or [h]

11. Notes About the Meta-Analysis Reported in Chapter 6
31 studies from English-language journals
Studies are numbered in Table 6.1 and cited with superscripts
Errors are listed if they occurred in
Over 5% of opportunities across the data collections
Over 5% of the children in the samples

12. 2-Year-Olds Focus Questions
How is accuracy different for vowels and consonants?
How is the phoneme inventory different for early and late 2-y-olds?
What classes of consonants are in the inventory at age 2;11? Missing or mostly missing from the inventory?
Table 6.2 Summary of phonological development from 2;0 to 2;11 years of age

13. Table 6.4 Error patterns observed for children aged 2;0-2;11, reported by percentage frequency of occurrence across the group, and percent of children producing the pattern (n/a notes unavailable data)
Focus Questions
Which types of phonological processes are seen most frequently in the overall productions of 2-year-old children (column 3)?
Which types of phonological processes are seen in the greatest proportion of children (column 4)?
What could explain the difference between the high percentages of children who show certain errors and the overall low incidence of the errors across the samples?

14. 3-Year-Olds Focus Questions
How has the consonant inventory changed from age 2 in terms of sound classes?
What are some troublesome sounds that 75% but not 90% of 3-year-olds can produce?
What is the predominant word shape?
Table 6.5 Summary of phonological development from 3;0 to 3;11 years of age

15. How are these findings different from children age 2 years?
Table 6.7 Error patterns observed for children aged 3;0-3;11 reported by frequency of occurrence and percent of children producing the pattern (n/a notes unavailable data)
Focus Questions
Which types of phonological processes are seen most frequently in the overall productions of 3-year-old children (column 3)?
Which types of phonological processes are seen in the greatest proportion of children (column 4)?
How are these findings different from children age 2 years?

16. 4-Year-Olds Focus Questions
How have PCC and PVC changed from age 3 years?
How has the consonant inventory changed since age 3 years in terms of sound classes?
Which are the most troublesome sounds at age 4 years (those that 75% of the children can produce but not 90% of them?)
Table 6.8 Summary of phonological development from 4;0 to 4;11 years of age

17. How are these findings different from children age 3 years?
Table 6.10 Error patterns observed for children aged 4;0-4;11 reported by frequency of occurrence and percent of children producing the pattern (n/a notes unavailable data)
Focus Questions
Which types of phonological processes are seen most frequently in the overall productions of 34-year-old children (column 3)?
Which types of phonological processes are seen in the greatest proportion of children (column 4)?
How are these findings different from children age 3 years?

18. Ages 5 to 9 Years Focus Questions
Table 6.11 Summary of phonological development from 5;0 to 9;11 years of age
Focus Questions
What are the last phonemes to be acquired between age 5 and 9 years?
What are the last few phonological processes observed in children in this age range?

19. What trends are evident across ages 5 to 7 years?
Table 6.13 Error patterns observed for children aged 5;0-7;11 reported by frequency of occurrence and percent of children producing the pattern (n/a notes unavailable data)
Focus Questions
What trends are evident across ages 5 to 7 years?
If a 7-year-old child still says [gwin]/green, how unusual is that?

20. From a Synchronic to a Diachronic Perspective
Synchronic: investigating many characteristics of a sample at one point in time
Diachronic: investigating one characteristic across time

21. Accuracy
Figure 6.1 Measures of accuracy (PCC, PVC and PPC) across the targeted age range: means are represented by the points, and error bars represent +/- 1 standard deviation averaged across studies

22. Table 6.14 Phonetic and phonemic inventory for children across the targeted age range; blank cells denote accuracy below 75%; n/a notes unavailable data
Inventory

23. Error Patterns
Figure 6.2. Percent Frequency of Occurrence of the three categories of error patterns across the targeted age range: (a) Assimilation Patterns; (2) Substitution Patterns; and (3) Syllable Structure Patterns.

24. Connections
Chapter 1 reviews the history of child phonology and describes different theoretical approaches to studying typical speech development
Chapter 2 provides a an overview of measures to describe and measure child speech development
Chapters 4 and 5 describe pre-speech and speech development in infants and young toddlers
In Chapter 9 on crosslinguistic trends, developmental trends for sound inventories by sound classes and trends for error patterns are mentioned.
In the chapters on speech sound acquisition in languages other than English, language-specific patterns of acquisition are described
Chapter 20 on diagnostic guidelines shows how to use normative data to determine the presence and nature of a speech delay or disorder

25. Concluding Remarks
By age 4 years, children have a large phoneme inventory and are able to use it with increasing accuracy
Speech development does not occur in isolation; it goes hand in hand with other areas of development, for instance lexical and syntactic growth
The milestones of typical development provide guidance when assessing a child for the presence of a speech delay or disorder

26. Sidebar 6.1 Feature Production
Instead of looking at inventories, some researchers have reported on the development of feature contrasts. Children are thought to build their phonological system by establishing feature contrasts (Jakobson, 1968), thus the goal is to identify the features that children are contrasting and the order in which the feature contrasts are acquired. Stokes and colleagues14 have reported on the percent of two-year-old children that contrast different features. They found that 100% of children produced the consonantal, sonorant, coronal and voicing contrasts, that 75-95% of children produced the anterior, continuant and nasal contrasts, and that less than 50% of children produced a delayed release (i.e., affricates), lateral or strident contrasts. Based on their research, Prather et a.l 12 proposed the following order of feature acquisition (from earliest to latest): continuant, strident, diffuse, voice, nasal, grave.

27. Sidebar 6.2 Prosody
Beyond segmental accuracy, it is important to consider stress, intonation, and rate. As is noted in Chapter 7, few studies have described the prosody of preschool aged children, despite the important role it can play in word accuracy. Rate has been studied among three-year-old children from New Zealand and the United States of America28. This studied showed that children from New Zealand speak a little faster than their American peers with a rate of syllables per minute of 208 versus 182, respectively. Regarding the length of utterances, the mean number of syllables per utterance was 4.7 for New Zealand and 4.5 for American children. Intonation has been studied among 5-year-old children29. Children were found to use the basic functions of intonation, including chunking, affect, and focus. Children, however, have been found to have difficulty incorporating two words to correctly mark the stress of a compound word. For example, children have difficulty shifting the stress placement from the noun in “a black bird”, to the first syllable in “a blackbird”. Children at this age also have difficulty placing the phrase-level accent in non-final position for indicating a change in focus (“The CAT jumped on the hat”). These abilities continue to improve through to the age of 13 years.