Asymmetry of neural circuits for word and face recognition in readers of Roman and Arabic script

Words and faces preferentially engage regions in opposite hemispheres of the brain, with corresponding differences in recognition ability between the visual fields. These face and word asymmetries have not been compared simultaneously in readers of different scripts. We compared cortical and behavioural laterality between monolingual readers of Roman or Arabic script, and bilingual readers of both scripts, to evaluate whether reading experience and script properties (e.g., reading direction), alter the representation of words and faces. Cortical activation was measured using 3T fMRI in 21 subjects (6-8 per language group; 3 groups) who viewed faces, English and Arabic words, and control stimuli, whilst performing a one-back task. Cortical regions of interest (ROI) were identified for faces (contrast: faces > phase-scrambled faces and faces > houses; ROIs: fusiform face area, occipital face area, superior temporal sulcus), and for English and Arabic words (contrast: words > phase-scrambled words; ROI: visual word form area). BOLD activation and number of voxels were measured in each ROI. Behaviour was measured outside the scanner in four tasks involving stimuli presented in the left or right visual field (lexical decision, same-different word discrimination, 10AFC face identification, chimeric face identity), with eye movements monitored throughout. We found effects of group on cortical and behavioural laterality for words and faces both. All groups showed cortical left-hemispheric dominance for words in the habitually-read script, but this effect was strongest for English readers, and only English readers showed superior word recognition in the right than left visual field. Likewise, cortical right-hemispheric dominance for faces was strongest in English readers, intermediate for bilinguals, and was virtually absent in Arabic readers. These effects were paralleled in chimeric face judgements. Thus, reading experience or the properties of the habitually-read script alter the symmetry of neural representations for words and faces.