Exploring vernacular reorganisation in a longitudinal corpus of pre-schoolers’ speech

Joshua Wilson Black and Lynn Clark

Overview

Overview

1. Background and Research Questions
2. Data
3. Analysis
4. Results
5. Interpretation

[Greeting]

I’ll start by 1. giving some background on vernacular reorganisation, the question of the onset of vernacular reorganisation, and set out a couple of research questions. I’ll then 2. tell you a bit about our data before turning to (3.) the analysis we applied. I’ll conclude with (4.) a discussion of our results and 5. what they mean for our research questions.

The Team

Joshua Wilson Black (Postdoc)

Lynn Clark (PI)

Robert Fromont (Software)

Gail Gillon (AI)

Brigid McNeill (AI)

Amy Scott (AI)

Grant: 20-UOC-064

Here’s the team. I’m was a postdoc at NZILBB at the University of Canterbury for the majority of this project, but am now in a lecturer role.

Lynn Clark is the PI on the project. The NZILBB software developer, Robert Fromont, has had a lot of work to do. Finally, Gail, Brigid and Amy are members of the team which collected our data and are AIs on the project.

Background

Vernacular reorganisation

[…] we necessarily begin with the phonetics, phonology, morphology, and syntax that we acquired from our first caretaker, normally female. The general condition for linguistic change can then be stated in a very simple way: children must learn to talk differently from their mothers. Let us refer to this process as vernacular re-organization. (Labov 2001, 415)

We investigate the onset of vernacular reorganisation.

‘Vernacular reorganisation.’ What is it? It is a bit of a vague term which was defined by Labov as (give full quote).

The idea is that, given well known patterns of generational change in language, there must be some process by which children come to speak differently from their parents even though they must, Labov says ‘necessarily’, begin with the language we aquire from our ‘first caretaker’.

The process of vernacular reorganisation takes time, and has an onset.

Vernacular reorganisation

(Labov 2001, 448)

(Labov 2001, 448)

1. Transmission: Acquire caregiver’s vernacular.

2. Incrementation: Advance linguistic changes underway in the community.

Trigger: shift from caregiver-dominated norms to peer-dominated norms around 4-5 (usually at school).

This plot is frequently used to illustrate Labov’s model of vernacular reorganisation. This is the expected movement of an individual speaker in F2 for an unnamed vowel which is taken to be fronting in the community as the speaker ages.

The imagined speaker starts at their caregiver’s level. The acquisition of the caregiver’s vernacular is called transmission.

Then, at sometime between 4 and 5, but around at 4 in the plot here, the speaker departs from the caregivers model and begins to use more innovative variants as they age. This process is called incrementation.

At a later stage, we get stabilization, but this is not the topic of our work.

It is also worth noting that this model, as originally stated, assumes that the caregiver is female and that only female children engage in incrementation. Male children pick up their caregivers vernacular, while female children go ahead of it. This is supposed to explain the one-generation lag sometimes seen between male and female speakers with respect to sound changes.

Research Questions

1. Is there evidence of vernacular reorganisation in the speech of preschool aged children?
2. Are all changing accent features advanced at the same time and at the same rate during incrementation?

1. The overall aim of our research is to understand how children’s vowel production changes over the period that spans their pre-school years.

In Labov’s model, the child’s transition to school at around 5 years of age and this is expected to mark the time when parental influence begins to wane and the peer group becomes important. But what if this happens sooner? What if there is already evidence of vernacular reorganisation happening within the preschool stage?

There are a few reasons we might expect to see evidence of vernacular reorganisation in children younger than school age. Labov’s model seems to hinge on a fairly outdated assumption that children undergo a kind of social awakening when they transition from home-based care to school. However, most children these days don’t transition from home-based care directly to school (in NZ most children spend at least 20 hours per week in an ECE setting with other children). Moreover, many studies on the acquisition of sociolinguistic variation have found adult-like patterns of linguistic and social variation in the speech of very young children (as young as two).

2. If we do find evidence of vernacular reorganisation going on in pre-school years, what does that look like? For instance: are all changing accent features advanced at the same time and at the same rate during incrementation?

Data

Story Retell

• Source: the UC Child Well-Being Research Institute’s Better Start Literacy Approach | Te Ara Reo Matatini.

• Children were presented with a story and asked to retell it in their own words.

• Two stories were used: Hana and the Tūī and Tama and the Playground (Gillon, McNeill, and Scott 2019).

• Both stories were written by the CWRI to match the NZ cultural context and contain a wide variety of literacy-relevant linguistic features (Gillon et al. 2023; Scott et al. 2022).

Our child speech data comes from a series of story retell tasks carried out by preschoolers in Christchurch New Zealand. The data were recorded by our collaborators in the Child Wellbeing Research Institute as part of a large government-funded study called the “Better Start Literacy Approach” project.

Part of the suite of literacy measures applied by CWRI was a story re-tell task. Two stories were used: Hana and the Tui and Tama and the Playground. Both stories were constructed to contain a wide variety of vowel and consonant sounds and to match the New Zealand cultural context (Gillon et al. 2023; Scott et al. 2022).

Children were presented with a recorded voice and a series of still images (like this one).

After hearing the story and viewing the images, the children were shown the images again and asked to tell the story in their own words.

We were given access to anonymised transcripts and audio recordings from these preschoolers from multiple early childhood centres across Christchurch.

Tell:

Retell:

Preschooler corpus

• 18 centres
• 132 children
• F: 76, M: 65
• 60 with two recordings
• 19 with three recordings
• 2 with four recordings

After filtering:

Preschooler corpus

• 101 NZ European
• 19 Māori
• 2 Pasifika
• 6 Asian
• 4 Other
• Age at recording: 3;11 - 5;5
• Median age: 4;6

Preschooler corpus

• dress: 968 (F1), 961 (F2)
• fleece: 1150 (F1), 1159 (F2)
• kit: 1888 (F1), 1848 (F2)
• nurse 444 (F1), 447 (F2)
• trap 987 (F1), 963 (F2)

QuakeBox

Source: Wayne Williams (Port Hills Productions

• 431 single-speaker recordings
• Prompt: “tell us your earthquake story”.
• Recorded across a range of sites in Christchurch in 2011-2012.
• Our community baseline (caregivers: F 18-35, Oldest generation: F 76+)
• High quality audio and video recordings.

Our data comes from the QuakeBox corpus (Clark et al., 2016). The corpus has 431 speakers who freely respond to the prompt ‘tell us your earthquake story’. The recordings were made in a range of locations across Christchurch in the wake of the Christchurch earthquakes of 2010 and 2011.

This corpus functions as our baseline for the community. We treat the female speakers who were betwen 18 and 35 at the recording point as our notional caregiver generation. That is, as the generation which are assumed to be the sole caregivers in the usual version of the vernacular reorganisation hypothesis. We use the oldest two age categories (76+) as our ‘oldest generation’.

The recordings were made with high quality audio and video equipment.

The corpus is stored in LaBB-CAT and run through HTK forced alignment (Fromont and Hay, 2008). LaBB-CAT then interfaces with Praat to perform formant tracking.

Analysis

Preprocessing

1. Transcription from CWRI.
2. Correction of timestamps.
3. Forced alignment (see Fromont et al. 2023).
4. Formant tracking (via FastTrack (Barreda 2021) with manual checking).
5. Normalisation

• Watch out: Kids data raises many problems — be careful! ⚠️
  • See supplementary materials of full paper.

Modelling Approach

1. We don’t have all the data we need to directly test core hypotheses
   • …so we go exploratory.
2. We want to discern an onset in sound change
   • …so we use GAMMs.
3. Data is sparse and model convergence difficult
   • …so we adopt a Bayesian approach (via brms: Bürkner 2017)

1. The original design for this project included recordings of caregivers and recordings of children both at pre-school and once they arrived in school.

For various reasons, prominently Covid-19 and the unanticipated level of difficulty in processing the data we did get, we were not in a position to do a confirmatory investigation of the vernacular reorganisation model.

Nonetheless, our data set offers a unique exploratory resource for looking at the earliest stages of the development of an accent.

2. We are interested in ‘onset’ points — if there are any, we can’t simply fit a straight line through the data. So we use GAMMs — a very flexible way to fit nonlinear curves through data.

3. our data is quite messy and convergence is difficult for model. We adopt a Bayesian approach primarily to increase the flexibility of our model structure and encourage convergence.

Model structure

For dress, fleece, kit, nurse, and trap (the ‘extended short front vowel shift’), F1 and F2 we fit the following model:

formant_value ~ gender + stopword + s(age_s, by=gender, k = 4) + (1|word/unstressed) + (1|participant/collect)

• Similar models fit to QuakeBox.

Results

e.g.:

This plot carries our main findings – so we’ll spend a bit of time on this slide getting familiar with all that it is showing.

This figure shows model predictions of five monophthongs, for three populations, plotted on a single vowel space:

• the children’s vowels – the youngest children are represented as circles and the oldest children are represented as arrow heads; change over real time in the children is represented with a line connecting the circles and the arrow heads.
  
• the youngest females in our QB data (represented by diamonds) who should provide us with a sample of speech that is relatively similar to the female caregivers in this community.
• the oldest generation in the QB data. Comparing the Caregivers generation to the Oldest female generation gives us a picture of ongoing community change for females in this community using apparent time data. And comparing the change over time in the children with this gives us a picture of whether or not we’re seeing evidence of vernacular reorganisation at this age and stage.

Now let’s go through each vowel. Note that vowel predictions are from 50 months to 60 months (4;2–5), to avoid plotting potentially spurious movements at the edges of our data range.

The preschoolers start with high front realisation of FLEECE, higher than the caregiver level, and this continues to raise over the next year and a half. This is in the opposite direction of community change.

The children seem to be starting out with relatively conservative realisations of dress, lower than either the caregiver population or the older speakers. We see them raise the vowel over their pre-school years although the predicted value at 60 months is not yet close to the caregiver level.

The children’s realisations at 50 months have higher and fronter realisations of KIT than the adults. This changes over time, so that by 67 months both the boys and girls show lower and more centralised realisations of KIT, although still some way away from the central realisations produced by the caregivers or older speakers.

There is no clear movement over time in the childrens’ speech for nurse (teal) or trap (pink). BUT They are both significantly lower and backer (NURSE) in the vowel space than the community reference points. The line for NURSE in the male speakers is not reflective of a large amount of data and should be taken with a grain of salt. The confidence bars on the relevant models are very wide.

So a mixed bag here. But is there any discernible onset time for these changes?

Remember that the overall aim of our research is to understand how children’s vowel production changes over the period that spans their pre-school years.

The original vernacular reorganisation model lays out the expectation that the child’s transition to school at around age 5 is expected to be the catalyst for the onset of vernacular reorganization, in which sound change away from the caregivers begins.

We were interested to know what is happening in the lead up to this time, and whether there is perhaps evidence of vernacular reorganisation from a much younger age, because the transition to school is no longer such a massive social change for children.

Here, I’ve picked out the four most obvious changes in the vowel space plot we’ve just been peering at: FLEECE F1, DRESS F1, KIT F1, and KIT F2. Females are in red and males in blue. Horizontal lines are the same ‘caregiver reference’ levels used in the previous plot. The rug below the plot indicates the presence of actual data points. We don’t want to over-interpret ‘wiggles’ in areas of low data density!

The same story is visible in all of these plots: there is no obvious place at which the changes ‘take off’ over the period we are looking.

DRESS F1 perhaps comes closest to canonical descriptions of vernacular reorganisation – there is some overlap between the male children and the caregiver distributions at age 3;5. By age 5 both male and female children are getting close to the caregivers but not yet advancing the change.

In both F1 and F2 space, KIT is fairly stable for the adult population. In both cases, the children start off somewhere far more conservative (i.e. the children have a higher fronter KIT realisation, quite unlike the centralised KIT that is typical of NZE). Over time they work towards this more canonical NZE realisation by lowering (females) and backing (males) their KIT realisations, but they still don’t quite reach the adult norms by the age of 5, especially not in the F2 dimension.

And FLEECE seems to be different again. FLEECE has been lowering in Christchurch for some years. But the children start off with a higher FLEECE vowel than the community and instead of converging on the community over time, they continue to raise it, moving in the opposite direction from the community and away from the caregiver norm.

Results summary

• Is there evidence of vernacular reorganisation in the speech of pre-school aged children?
  • Both stability and change.
  • No ‘elbow’ in the smooths indicate rapid acceleration of change (incrementation).
  • Difficult to interpret these straightforwardly as vernacular reorganisation.
    • fleece is going the wrong way!
• Are all changing accent features advanced at the same time and at the same rate during incrementation?
  • Not all features are changing.
    
  • Some are changing faster than others.
    
  • Some are changing differently for males and females.

Interpretation

Developmental?

• Greater variation in kids than community.
• Donegan (2012): children achieve ‘quite acceptable vowel quality’ before 3 (also Vorperian and Kent 2007).
• But: large variability in vocal tract length and vowel targets up to age 10 (e.g. Roepke and Brosseau-Lapré 2021; Brosseau-Lapré and Roepke 2019).

Donegan (2012:29) explains that “variability of vowels is not surprising when we consider the difficulty of controlling the shape of the tongue, which is a complex three-dimensional network of intrinsic longitudinal, vertical, and transverse fibers”. However, he goes on to say that there is enough evidence from a range of different languages to suggest that “many children achieve quite acceptable vowel quality before age three in all but the rhotic vowels” (2012:29).

Vorperian & Kent (2007) review data from 21 studies of F1 & F2 measurements of the four corner vowels in children from 8 months to 11 years. From age 3, the position of the vowels in the corners of the vowels space is shown to be relatively stable and remains this way across childhood (2007:1517).

The implication from this literature, then, is that most vowel quality development happens before the age of 3 and so there seems to be no developmental reason to expect that children from 3 years onwards can’t accurately produce the vowels under investigation in this study.

However, another literature suggests we shouldn’t be too quick to exclude developmental effects. Phonetic studies have found very large variation in both vocal tract length and vowel target accuracy. More inter(sub)disciplinary work is needed here.

CDS/Story-book speech

• Kids vowel spaces suggest hyper-articulation.
• First thought: kids primed by storyteller?
• Second thought: kids learn hyper-articulated vowels before developing the ability to hypo-articulate (see Ménard et al. 2020).

• We can’t exclude development effects. (More inter(sub)disciplinary is work needed).

The preschoolers vowel spaces show evidence of hyperarticulation.

A first thought, which is evidenced in this plot, is that the children are perhaps being primed by the hyperarticulated story book style or are actively copying/mimicking that style.

Now let’s look at what happens when we overlay the vowels from the story (squares with crosses connected by thin dashes). The storyteller also seems to have features of hyperarticulation – notice the much lower TRAP, and much higher FLEECE than is typical for adult speech in NZE NURSE is also quite far back (even further back than it is for the kids). Notice how much smalled the vowel space for the caregivers generation is (connected by the solid lines).

As a second thought, we return to the recent phonetic literature on early phonetic development. Lucie Menard et al (2020) present evidence that children first learn hyper articulated vowels before developing the skills to hypo- articulate.

There’s no possible way for us to know (with the data that we have) whether this is unconscious priming, whether the children are mimicking the storyteller’s style of speech, or whether this is a developmental effect.

Or perhaps all three. But this data, and the wider phonetic literature, open a space for future, more phonetically informed, work in sociolinguistics on the early stages of vernacular re-organisation.

Upshot

• We’ve found sound change before kids start school.
• No ‘elbow’, or point at which incrementation begins.
• Some changes, e.g. dress raising look like vernacular reorganisation.
• But fleece looks entirely different.
• Possible influence of CDS/Story-book speech and developmental hyperarticulation.
• Focus on multiple variables at once is vital for this kind of project.

We’ve found some interesting and unexpected stuff. For instance, we found some change over time during a period of time where the model suggest there should be stable variation. And we found no evidence of an ‘elbow’ like this one i.e. no rapid acceleration of change for those vowel that were changing. We found some changes that look like the beginning of vernacular reorganisation (e.g. DRESS raising) and others that look entirely different (but can likely be explained by other phenomena such as priming or stylistic devices).

In addition to the phonetic complexity which needs to be incorporated into the sociolinguistic account of early vernacular development, we think that our study highlights the importance of stepping away from a single-variable approach, which is a methodology that has dominated work in studies of language variation and change for many years. If we had selected any one of these vowels to investigate in isolation, we would have missed the complexity and the systematicity in these data.

Thank you very much for your attention!

References

Barreda, Santiago. 2021. “Fast Track: Fast (Nearly) Automatic Formant-Tracking Using Praat.” Linguistics Vanguard 7 (1). https://doi.org/10.1515/lingvan-2020-0051.

Brosseau-Lapré, Françoise, and Elizabeth Roepke. 2019. “Speech Errors and Phonological Awareness in Children Ages 4 and 5 Years with and Without Speech Sound Disorder.” Journal of Speech, Language, and Hearing Research 62 (September): 3276–89. https://doi.org/10.1044/2019_jslhr-s-17-0461.

Bürkner, Paul-Christian. 2017. “brms: An R Package for Bayesian Multilevel Models Using Stan.” Journal of Statistical Software 80 (1). https://doi.org/10.18637/jss.v080.i01.

Donegan, Patricia. 2012. “Normal Vowel Development.” In Handbook of Vowels and Vowel Disorders. Taylor & Francis.

Fromont, Robert, Lynn Clark, Joshua Wilson Black, and Margaret Blackwood. 2023. “Maximizing Accuracy of Forced Alignment for Spontaneous Child Speech.” Language Development Research 3 (1). https://doi.org/10.34842/shrr-sv10.

Gillon, Gail, Brigid McNeill, and Amy Scott. 2019. Tama and the Playground. University of Canterbury Child Wellbeing Research Institute.

Gillon, Gail, Brigid McNeill, Amy Scott, Megan Gath, and Marleen Westerveld. 2023. “Retelling Stories: The Validity of an Online Oral Narrative Task.” Child Language Teaching and Therapy, 02656590231155861.

Labov, William. 2001. Principles of Linguistic Change: Social Factors. Wiley-Blackwell.

Ménard, Lucie, Amélie Prémont, Pamela Trudeau-Fisette, Christine Turgeon, and Mark Tiede. 2020. “Phonetic Implementation of Prosodic Emphasis in Preschool-Aged Children and Adults: Probing the Development of Sensorimotor Speech Goals.” Journal of Speech, Language, and Hearing Research 63 (June): 1658–74. https://doi.org/10.1044/2020\_jslhr-20-00017.

Roepke, Elizabeth, and Françoise Brosseau-Lapré. 2021. “Vowel Errors Produced by Preschool-Age Children on a Single-Word Test of Articulation.” Clinical Linguistics &Amp; Phonetics 35 (January): 1161–83. https://doi.org/10.1080/02699206.2020.1869834.

Scott, Amy, Gail Gillon, Brigid McNeill, and Alex Kopach. 2022. “The Evolution of an Innovative Online Task to Monitor Childrens Oral Narrative Development.” Frontiers in Psychology 13 (July). https://doi.org/10.3389/fpsyg.2022.903124.

Vorperian, Houri K., and Ray D. Kent. 2007. “Vowel Acoustic Space Development in Children: A Synthesis of Acoustic and Anatomic Data.” Journal of Speech, Language, and Hearing Research. https://doi.org/10.1044/1092-4388(2007/104).

Extra: Formant tracking settings

Upper limits:

• Front vowels get 6000-9000 Hz.

• Back vowels get 5000-8000 Hz.

• Other vowels get 5500-8500 Hz

• ‘Front vowels’ (NZE) = fleece, dress, nurse, goose, trap, kit

• ‘Back vowels’ = lot, thought, foot

• ‘Others’ = strut, start

By-vowel limits:

• FLEECE: f2 > 1500,
• DRESS: f2 > 1500,
• GOOSE: f2 > 1000,
• NURSE: f2 > 1200,
• THOUGHT: f2 < 2250,
• LOT: f2 < 2500
• FOOT: f2 > 900
• KIT: f2 > 1250

Formant bounds:

label f1lower f1upper f2lower f2upper f3lower f3upper START 350 1500 1200 3500 0 5000 THOUGHT 350 1500 1200 2250 0 5000 TRAP 350 1500 1200 3500 0 5000 NURSE 350 1500 1200 3500 0 5000 DRESS 350 1500 1500 4000 0 5000 FLEECE 350 1500 1500 4000 0 5000 KIT 350 1500 1250 3500 0 5000 LOT 350 1500 1200 2500 0 5000 GOOSE 350 1500 1000 3500 0 5000 FOOT 350 1500 900 3500 0 5000 STRUT 350 1500 1200 3500 0 5000