Distinguishing a phonological encoding disorder from Apraxia of Speech in individuals with aphasia by using EEG

As we speak, various processes take place in our brains. We find the word, find and organize the speech sounds and program the movements for speech. A stroke may cause impairment at any of these processes. Usually, multiple processes are affected. Existing methods to distinguish a disorder in finding and organizing speech sounds (phonological encoding) from an impairment in programming the articulation (Apraxia of Speech) are not optimal. In this thesis, it was studied whether EEG, measuring small changes in electric brain activity with electrodes that are placed on the scalp, can be used for this purpose. A protocol was developed to trace the processes of speech production, which was successfully tested in a group of younger and one of older neurologically healthy adults. In the younger and older adults, the processes were registered at the same electrodes on the scalp, but the time window and the waveform of the processes differed. In individuals with a phonological encoding disorder and those with Apraxia of Speech the disordered processes could not be identified, because the severity of the impairment in the groups varied. Their impaired processes differed from those in neurologically healthy individuals. Also, because of their disorder in the previous stage, the programming of the articulation was different in individuals with a phonological encoding disorder. The protocol can distinguish a phonological encoding disorder from Apraxia of Speech due to differences in the EEG data (relative to neurologically healthy participants) that only were observed during programming movements for speech.