ERP Correlates of semantic and syntactic processing in pre-verbal cochlear implant users

Artesini, L. 1 , Vespignani, F. 2 , Musola, D. 3 , D'Avanzo, V. C. 2 , Ragusa, E. 2 , Chini, A. 5 , Bonfioli, F. 5 , Frau, G. N. 5 & Pavani, F. 1, 2, 4

1 CIMeC - Center for Mind/Brain Sciences, University of Trento, Italy
2 Department of Psychology and Cognitive Science, University of Trento, Italy
3 Cooperativa Logogenia, Italy
4 Centre de Recherche en Neuroscience de Lyon, France
5 Santa Maria del Carmine Hospital, Rovereto, Italy

Profound deafness can limit language acquisition, impacting on oral and written language processing. Research on the latter in deaf children revealed specific difficulties in syntactic and grammatical abilities, even in individuals who partially recovered hearing through cochlear implants (CI). In agreement with these behavioral results, EEG studies in congenitally deaf adults without CI showed typical N400 responses triggered by semantic incongruities, but no P600 effects in response to syntactic violations.
To evaluate the impact of CI on written sentence processing, we tested 15 early deaf CI users and 48 normal-hearing controls, using EEG and behavioral measures.
In CI users and normal-hearing controls alike, we documented N400 and P600 responses to semantic and syntactic violations, respectively. Thanks to the high number of items per condition, these results are also quantifiable at a single subject level. Interestingly, in the syntactic condition a larger P2 responses in CI users compared normal-hearing controls was found at left-frontal sites.
Taken together these results suggest that CI usage can promote hearing-like brain responses to syntactic violations (intact P600), with possibly greater reliance on orthographic rather than phonological processing in the early stage of detection of the morphosyntactic violation (enhanced P2).