Language processing deficits may occur at stuttering onset

A study of preschool-age children has shown key differences in the neural networks mediating language processing between those who stutter and those who do not.

Specifically, children who stuttered demonstrated slower, less efficient lexical access and integration than children who did not stutter, as well as poorer syntactic processing.

"The present findings are the first to show that differences in electrophysiological measures of language processing occur near the onset of stuttering and thus may play an important role in the development of the condition," say Christine Weber-Fox, from Purdue University in West Lafayette, Indiana, USA, and colleagues.

Neural indices were elicited by measuring the event-related brain potentials (ERPs) from each child as they watched a cartoon and heard naturally spoken sentences that were correct or contained semantic or syntactic (phrase structure) violations.

ERPs in children who stuttered were characterized by longer N400 peak latencies for both correct words and semantic anomalies, compared with children who did not stutter. This indicates less efficient and slower processes for lexical access and integration, says the team.

Syntactic violations elicited early negativity that was larger over medial electrode sites in the children who stuttered than in those who did not.

Furthermore, the amplitude of the P600 elicited by syntax violations relative to control words was concentrated over the left hemisphere for children who did not stutter, but showed the reverse pattern in children who did stutter with a marked effect only over the right hemisphere.

"These findings suggest possible differences in the functional neural organization for processing of phrase structure violations in CWS [children who stutter] compared to their typically fluent peers," the team writes in the Journal of Fluency Disorders.

The authors acknowledge that although the findings suggest the impact of atypical neurophysiology on language processing in children who stutter, future studies are needed to determine whether these discrepancies in neural indices have a casual link to stuttering in children with the speech impairment.

Previous research has already demonstrated that preschool children who stutter have more variable and fragile speech motor control systems when challenged with higher speaking demands.

However, the present findings provide evidence that even in the absence of any speaking demands, these children show distinct electrophysiological differences in processing language when compared with their fluent peers.

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