Perrone-Bertolotti, M. 1, 2 , Cousin, E. 1, 2, 3 , Yvert, G. 1, 2 , Pichat, C. 1, 2 & Baciu, M. 1, 2
1 Laboratoire de Psychologie et Neurocognition, UMR CNRS 5105, Université Pierre Mendès-France, Grenoble, France
2 SFR « Santé et Société », Université Pierre Mendès-France, Grenoble, France
3 SFR« RMN Biomédicale et Neurosciences », Unité IRM 3T, Université Joseph Fourier, Grenoble, France
This fMRI study explores how the cerebral activity for phonological processing is modulated by the difficulty level of grapheme-to-phoneme conversion (GPC; transparent vs. non-transparent) and the gender of participants (male vs. female). Transparent (T) GPC indicates low level while non-transparent (NT) GPC indicates high level of difficulty. Twenty two right handed French native speakers (11 male) participated to experiment. They performed visually a phoneme detection (Language, L) and a visuo-attentional (Control, C) tasks. According to GPC difficulty level, the L stimuli were built as T and NT. A 3T MR scanner was used for acquisition. Using SPM5, the L vs. C contrast was calculated first at individual level (GLM analysis) and then to group-level (random-effect analysis). Several regions of Interest (ROI) were defined and the MR signal intensity variation (% MR, parameter estimates) was extracted from each of them. Based on the parameter estimates values, ANOVA analysis determined if the GPC and the gender showed significant effect on cerebral activity.
Our results showed that behavioural performances were modulated by GPC with more accurate phoneme detection when the items were T with respect to NT. At the cerebral level, the left-hemisphere activity induced by phoneme detection was modulated by GPC difficulty level: T modulated the superior posterior temporal and NT modulated the inferior temporal gyrus activity. T modulation suggested automatic activation of phonological representations while NT modulation suggested verification and conversion of sub-lexical orthographic units toward phonological codes. Significant interaction between GPC and gender was observed: females showed higher accuracy of detection when the items were T and it was associated with greater activation of the lingual gyrus. Overall, our results suggest that cognitive mechanisms and cerebral correlates of phonological processing may depend on intrinsic and extrinsic variables, such as GPC and gender.