The Role of Broca's Area for Phonology During Visual Word Recognition: Investigations using Magnetoencephalography and Transcranial Magnetic Stimulation

This thesis explored a possible role of Broca's area (specifically the pars opercularis of left inferior frontal gyrus and neighbouring precentral gyrus; LIFGpo/PCG) in accessing sublexical phonology during visual word recognition. In Experiments 1 to 4, behavioural masked sublexical phonological priming effects were tested during lexical decision and reading aloud in English. No sublexical phonological effects were found during the lexical decision tasks, but significant sublexical phonological priming effects were found during reading aloud. In Experiment 5, masked sublexical phonological priming effects were then tested during a silent reading task using magnetoencephalography. Sublexical phonological priming effects were localised to LIFGpo/PCG within ~200 ms for real word targets and within ~75 ms for nonword targets. This indicates an early sensitivity to sublexical phonological information at LIFGpo/PCG during silent reading of English. In Experiment 6 chronometric functional magnetic resonance imaging guided transcranial magnetic stimulation was used to create focal and transient virtual lesions to LIFGpo/PCG in order to test the hypothesis that the putative early sublexical phonological representations seen at LIFGpo/PCG are functionally necessary for visual word recognition. Dutch participants underwent transcranial magnetic stimulation during reading aloud as compared to picture naming. An early disruption to word reading that was not present for picture naming would be evidence in favour of a necessary role of LIFGpo/PCG during early visual word recognition processes, as opposed to disruption of later speech production processes that are common to reading and naming. Experiment 6 failed to demonstrate that this region is functionally necessary for reading aloud prior to 200 ms in Dutch. The combination of findings in this thesis lead to many possible interpretations, which cannot be ruled in or out without further investigation. As yet, the functional significance of this early LIFGpo/PCG activation, therefore, remains unclear.