Head movements during MEG recordings in children may lead to inaccurate localization of brain activity. In this thesis, we examined the effects of head movements on source estimation in twenty children performing a simple auditory cognitive task. In addition, we tested the ability of a recently introduced spherical harmonic expansion method, signal space separation (SSS), to compensate for the effects of head movements on two source models: equivalent current dipoles (ECDs) and minimum norm estimates (MNE). In the majority of subjects, the goodness-of-fit of ECDs fit to the peak of the auditory N100m response was increased following the SSS correction compared with the averaged forward solution method proposed earlier. The spatial spread of ECDs as determined with a bootstrapping approach was also reduced after SSS correction. In addition, the MNE source estimates were spatially sharpened following SSS application, indicative of an increase in signal to noise ratio. Together these results suggest that SSS is an effective method to compensate for head movements in MEG recordings in children.

Poor readers perform worse than their normal reading peers on a variety of speech perception tasks, which may be linked to their phonological processing abilities. The purpose of the study was to compare the brain activation patterns of normal and impaired readers on speech perception to better understand the phonological basis in reading disability. Whole-head magnetoencephalography (MEG) was recorded as good and poor readers, 7-13 years of age, performed an auditory word discrimination task. We used an auditory oddball paradigm in which the 'deviant' stimuli (/bat/, /kat/, /rat/) differed in the degree of phonological contrast (one versus three features) from a repeated standard word (/pat/). Both good and poor readers responded more slowly to deviants that were phonologically similar compared to deviants that were phonologically dissimilar to the standard word. Source analysis of the MEG data using minimum norm estimation (MNE) showed that compared to good readers, poor readers had reduced left-hemisphere activation to the most demanding phonological condition reflecting their difficulties with phonological processing. Furthermore, unlike good readers, poor readers did not show differences in activation as a function of the degree of phonological contrast. These results are consistent with a phonological account of reading disability.

Reading difficulties appear to be related to a phonological deficit that has its origin in poor speech perception. As such, disabled readers may use contextual cues to compensate for their weak speech perception abilities. We compared good and poor readers, 7–13 years, on auditory perception of words varying in phonological contrast, in congruent vs. incongruent sentence contexts. Both groups did worse in the phonologically similar than in the phonologically dissimilar incongruent condition. Magnetoencephalography revealed differential activation between the groups as a function of phonological contrast in left superior temporal gyrus between 200–300 ms, suggesting that poor readers may have processed phonologically similar incongruent stimuli as congruent. The results are consistent with a phonological account of reading disability.