Visual word form processing in the right hemisphere: Evidence from neuropsychological investigations in two Chinese patients with a splenium lesion

Background: Though there is no doubt that the left hemisphere (LH) is the superior language processor, an increasing number of researches have demonstrated significant linguistic ability in the nonverbal right hemisphere (RH), such as orthographic processing and the superiority of recognising words presented in unfamiliar formats. However, it is difficult to rule out the role of the LH in language processing completely, because the subjects reported in most studies have no lesion or commissurotomy in the splenium of the corpus callosum (SCC), which allowed the interaction between left and right hemispheres in visual word processing. Patients with a lesion or commissurotomy in the SCC provide a unique opportunity to explore visual word form processing in the RH.Aims: The study involved a series of neuropsychological tests to investigate visual word form processing in the RH.Methods & Procedures: Two unique Chinese patients with a splenium lesion were asked to complete a series of neuropsychological tests, consisting of the Line Bisection Test, Albert Cancellation Test, the Aphasia Battery of Chinese (ABC), mini-mental state examination (MMSE) and visual word form processing (reading aloud, lexical decision in the Song typeface and handwritten styles) presented tachistoscopically in left or right visual field.Outcomes & Results: We found that two patients had difficulties in reading simple and compound Chinese characters presented tachistoscopically in the left visual field (LVF), called left hemialexia, while their lexical decision-making ability in the LVF was relatively spared. In addition, the two patients' performance on lexical decision-making in the LVF declined to a random level in the handwritten styles.Conclusions: These findings provide direct supporting evidence that the RH is important for processing a character's orthographic form and suggest that the LH is necessary for extracting an abstract presentation of a character in visual word form processing.