Children with developmental language disorder show less consistent maturation of speech-sound processing

A year-long study of Estonian preschoolers found that automatic neural responses to speech duration became more adult-like in typically developing children, but changed less clearly in those with developmental language disorder.

Children with developmental language disorder may process speech sounds more slowly and less consistently than their typically developing peers, according to a longitudinal study of Estonian preschoolers that tracked how children responded to quantity contrasts over one year.

Researchers followed 50 children aged four years six months to seven years five months, splitting them evenly between those with developmental language disorder and age- and sex-matched typically developing peers. The children were tested at two points 12 months apart, using both behavioural tasks and electroencephalography to measure the mismatch response, an event-related potential linked to automatic sound discrimination.

The study focused on Estonian quantity, a system in which meaning depends on both syllable length and pitch contour. In one test condition, the children heard a change in duration alone; in another, the sound changed in both duration and pitch contour. The researchers say the duration-only contrast produced a clear neural response that became more mature over time, while the combined duration-and-pitch contrast did not produce a reliable mismatch response in either group.

That pattern mattered. In the duration-only condition, the typically developing children showed a shift towards a more adult-like neural response over the year, with the early positive response shrinking and a later negative response becoming more pronounced. Children with developmental language disorder did not show the same clear within-group change, and at the second assessment they had a less pronounced negative response than their peers. Even so, the study did not find a statistically significant difference in the overall developmental trajectory between the two groups.

Behavioural results moved in the same general direction as the brain data. Children performed better on both discrimination tasks at the second assessment, with higher sensitivity scores and faster reaction times. They were also more accurate than children with developmental language disorder. But the researchers did not find a meaningful link between individual children’s behavioural scores and their neural responses, echoing earlier work suggesting that behavioural and pre-attentive auditory processing may not map neatly on to one another.

The authors argue that the gap may reflect the different demands of the two approaches. EEG measures capture automatic processing at the brain level, while behavioural tasks draw on attention, decision-making and, in the case of the lexical task used here, access to word knowledge. Because the stimuli were meaningful Estonian words, the neural response may also have reflected lexical processing rather than pure prosodic discrimination alone.

The findings add to a small body of longitudinal research suggesting that auditory processing in developmental language disorder does mature, but may do so more slowly or less consistently. They also reinforce the idea that children’s speech-sound processing is shaped by both acoustic sensitivity and language knowledge, a distinction that may matter when clinicians are deciding whether intervention should focus only on overt discrimination skills or also on earlier, automatic stages of speech perception.