Electropalatographic analysis of apraxia of speech in a left hander and in a right hander.

Two cases with 'pure' apraxia of speech are reported. The articulatory disturbances were quite similar. One of the two cases was a left-handed male with a subcortical haemorrhage and the other a right-handed male with a cerebral infarct. The MRI and CT scans showed that the first case had a lesion that mainly involved the right precentral gyrus and its deep white matter, and that the second had a lesion mainly affecting the lower parts of the left precentral and postcentral gyri and their deep white matter. These findings and a literature review suggest that a corticosubcortical lesion of the lower part of the left precentral gyrus in most right handers and a lesion of the symmetric region in the right hemisphere in some left handers cause apraxia of speech. The omission errors for sounds articulated by the tongue and the hard palate were analysed using electropalatography, which records visually the dynamics of the palatolingual contact. The results demonstrated that there were three kinds of omission errors: true omissions (no palatolingual contact); omissions with incorrect contact (palatolingual contact for a different sound or undifferentiated sound); and omissions with correct contact (correct palatolingual contact for a target sound). The latter two types of omission error were observed for initial consonants and they were probably caused by a delay in air flow. The patients also showed a tendency to substitute one of the two consonants/t, t/for other sounds, which suggested that they had difficulty in the inhibition of tongue activity.