Occipito-temporal contributions to reading

The debate regarding the role of ventral occipito-temporal cortex (vOTC) in visual word recognition arises in part from difficulty delineating the functional contributions of vOTC as separate from other areas of the reading network. Successful transcranial magnetic stimulation (TMS) of the area could provide a novel source of information regarding the area’s function, by offering the possibility of temporarily, non-invasively perturbing its information processing and assessing the consequences on behaviour. However, the area is often considered too deep to successfully stimulate with TMS. Thus the initial step was the demonstration of the feasibility of stimulation, which I proved in the first series of experiments. The stimulation resulted in a disruption in visual word recognition that was stimulus- and site- specific. The second series of experiments further investigated the stimulus-specificity, demonstrating that the nature of this specificity was task-dependent. The final series of TMS experiments in the thesis utilised the high temporal resolution of TMS to map out the dynamics of processing in both left and right vOTC, revealing hemispheric asymmetries in the time course of ventral occipito-temporal processing consistent for both visual words and objects. To complete these experiments, I acquired a large amount of functional localiser data for neuronavigated TMS. This allowed the investigation of the effectiveness of fMRI localisation for TMS and in addition the investigation of the important issue of how consistent the functional regions of interest (fROI) produced by these scans are. The first of two experiments showed these fROIs may have surprisingly poor reliability while the second investigated how best they can be optimised, maximising reliability. In conclusion, my PhD has demonstrated the feasibility and potential of using TMS to investigate vOTC contributions to visual word and object recognition, providing a novel source of information capable of informing the ongoing debate concerning vOTC