ABSTRACT: This fMRI study aims to assess the effect of two variables on the cerebral substrate of phonological processing during visual phoneme detection: (a) the difficulty level (type) of grapheme-to-phoneme conversion (GPC, letter-sound mapping) with two modalities, simple (S) and complex (C); and (b) the gender of participants, females (F) vs. males (M). The behavioral results have shown that simple items were processed more accurately than complex ones. At the cerebral level, phoneme detection activated the left-hemisphere phonological network and several regions of this network were modulated by the GPC type. Specifically, the activity of the superior posterior temporal gyrus was significantly higher for simple grapheme detection and suggests automatic activation of phonological representations; the activity of the inferior temporal gyrus was significantly higher for complex grapheme detection, suggesting greater demands of the integrative processes for solving competitive and inhibitory processes induced by the visual and phonological properties of stimuli. With respect to gender variable, we obtained significant interaction between GPC and gender. This effect showed higher accuracy for simple graphemes in females and suggests that female participants were more proficient than males for detecting simple items. This effect suggests easier and more rapid activation of phonological codes, probably based on a specific visual strategy, different from males. This is supported by the additional activation of the lingual gyrus in females for processing simple graphemes, although the exact explanation of this effect is not clear yet and requires supplementary experimentation and evidence. Overall, our results indicate that the cognitive mechanisms and cerebral correlates of phonological processing may depend on intrinsic and extrinsic variables, such as GPC and gender.
Journal of Neurolinguistics. 24(4):507-520.