Two cases with pure word dumbness were reported. The first case was a left-handed 27 year-old male who had a surgical operation for a subcortical hemorrhage in the right frontal lobe. NMR imagings showed a low density area in the inferior part of the right prefrontal gyrus involving its deep white matter. Within 10 days after the onset, the patient uttered only /a/ and /o/. At the stage of one month after the onset, a naming test was administered. The patient articulated correctly 45 words out on the total 240 test words. Articulatory errors were observed in the remaining 195 test words : substitution (61.7 %), omission (22.7 %), distortion(14.5 %) and addition (1.1 %). Further, electro-palatography, which visually records the dynamics of the palato-lingual contact, was employed to clarify the nature of omission. The results demonstrated that the palato-lingual contacts were appropriately achieved in the half of the omission errors. This suggested that some of the omission errors were caused by delay of the air flow and not necessarily by lack of the whole articulatory movements.
The second case was a right-handed 58 year old male who had a cerebral infarction. CT scans and NMR imagings showed a low density area in the inferior parts of the left pre- and postfrontal gyri involving their deep white matter. In the naming test of nine and half months after the onset, the patient committed errors in the 186 words out of the 246 test words. The remaining responses were substitution (78%), distortion (13%), addition (8%) and omission (1 %).
The articulatory characteristics common to these two cases were : 1) Consonant errors were more likely than vowel errors ; 2) Errors occurred more frequently in the initial position of a word than in other position ; 3) Substitution errors were more frequent than other error types, where the substitution for / t / and / t /was predominant and 4) the substitution due to the delay of voice onset time (for example, in / t / for / d /, / p / for / b /, etc.) were frequent.
