Inadequate information encoding linked to poor language ability

By Ingrid Grasmo

Study findings suggest that the impaired ability to retain and repeat unfamiliar phoneme sequences in children with specific language impairment (SLI) reflects inadequate encoding of phonologic information, rather than problems retaining encoded information.

"Encouraging to those attempting intervention with these children, we found good retention of material between sessions in children with SLI; despite their low levels of performance, their repetition scores were slightly higher after a 1-hour delay," say Dorothy Bishop (University of Oxford, UK) and colleagues.

The study also showed that after an initial exposure period, new phonologic sequences were remembered by children but decayed in adults, regardless of the initial language level of the participants.

The team asked parents and children from families where the child has SLI (n=18 adults; n=11 children) or does not have SLI (n=16 adults; n=14 children) to listen to three complex nonwords five times in two sessions (A and B) an hour apart.

Overall, children with SLI did poorly in nonword repetition compared with children without SLI, and showed less within-session learning than controls. PA similar trend was also seen for other participants in the study.

Both age groups showed evidence of learning, with scores improving from session A to B. However, the extent of improvement was significantly greater for children (mean score=7.74 to 9.02) than for adults (mean score=9.34 to 9.84).

The researchers say they had anticipated that individuals from SLI families would forget more during the 1-hour delay than controls, but adult scores declined between the last trial of session A and the first trial of session B in both groups. By contrast, there was an increase for all child participants.

"This was a surprising result, which supports the interpretation of nonword repetition deficits as an indicator of poor phonological encoding, rather than rapid decay of information in memory," say the authors.

Bishop and team had hypothesized that a ceiling effect on improvement in adults could be responsible for the decline in information retention over the delay, but the scores from adults with SLI families and those from control children diverged on the first trial of session B, despite being similar on the last trial of session A.

"The fact that the age bands differed regardless of the language level of the participants fits an explanation in terms of neuroplasticity," write the authors in Public Library of Sciences ONE.

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