An Application of Network Science to Phonological Sequence Learning in Children With Developmental Language Disorder

Abstract

Purpose: Network science has been a valuable tool in language research for investigating relationships between complex linguistic elements but has not yet been applied to sound sequencing in production. In the present work, we used standard error-based accuracy and articulatory kinematic approaches as well as novel measures from network science to evaluate variability and sequencing errors in speech production in children with developmental language disorder (DLD; aka specific language impairment).

Method: Twelve preschoolers with DLD and 12 age-matched controls participated in a 3-day novel word learning study. Transcription and articulatory movement data were collected to measure accuracy and variability of productions, and networks of speech productions were generated to analyze syllable co-occurrence patterns.

Results: Results indicated that children with DLD were less accurate than children with typical language at the segmental level. Crucially, these findings did not align with performance at the articulatory level, where there were no differences in movement variability between children with DLD and those with typical language. Network analyses revealed characteristics that were not captured by standard measures of phonetic accuracy, including a larger inventory of syllable forms, more connections between the forms, and less consistent production patterns.

Conclusions: Network science provides significant insights into phonological learning trajectories in children with DLD and their typically developing peers. Importantly, errors in word production by children with DLD do not surface as a result of weakness in articulatory control. Instead, results suggest that speech errors in DLD may relate to deficits in sound sequencing.

Figure 1.

Spatiotemporal index (STI). The top panel shows 10 productions of the same nonword extracted from a child's continuous speech signal. In the middle panel, the productions are normalized in time and amplitude, and the sum of the standard deviations is shown in the bottom panel to yield the STI.

Figure 2.

A sample of multiple productions of a single target, /f^ʃpəm/, visually depicted in network format. The period (.) indicates a syllable boundary.

Figure 3.

Graphical representation of the Jaccard index for Sessions 1 and 2. In the diagram on the left, the darkest gray region is 1 ∩ 2. In the diagram on the right, the entire gray region is 1 ∪ 2.

Figure 4.

Percent consonants correct (PCC) performance by session. DLD = developmental language disorder; TD = typically developing.

Figure 5.

Spatiotemporal index (STI) performance by session. DLD = developmental language disorder; TD = typically developing.

Figure 6.

Network visualizations for the group with developmental language disorder (top) and the typically developing group (bottom). Nodes correspond with the syllable sequence, and edges are depicted as the lines connecting nodes when two nodes were produced in succession. A thicker line indicates a more frequent pattern of production. Sessions 1–3 appear from left to right. Networks of children with developmental language disorder have more different syllables (nodes) and more different productions (edges).

Figure 7.

Two children in the group with developmental language disorder with typical performance on the Bankson-Bernthal Test of Phonology: Participants 1 (top) and 2 (bottom). Nodes correspond with the syllable sequence, and edges are depicted as the lines connecting nodes when two nodes were produced in succession. A thicker line indicates a more frequent pattern of production. Note that neither child stabilized on a single production with both showing multiple variations of the same form. Sessions 1–3 appear from left to right.

Figure 8.

Nodes (top), edges (middle), and edge weight (bottom) by session. DLD = developmental language disorder; TD = typically developing.

Figure 9.

Jaccard index representing the change in edges over time. DLD = developmental language disorder; TD = typically developing.