Selective Impairment of Phonetic and Non-Phonetic Transcription of Words in Japanese Aphasic Patients: Kana vs. Kanji in Visual Recognition and Writing

Abstract

Two aphasic subgroups of 10 each, with and without apraxia of speech, and two nonaphasic right- and left-hemiplegic groups of six each were administered two sets of tasks: 1) three visual recognition tasks in which kanji (ideogram) and hiragana (phonogram) representations of 10 highfrequency nouns and katakana representations of 10 comparative imported nouns were used as stimuli, and 2) two writing tasks with the same nouns using kanji, hiragana and katakana transcriptions. In the visual recognition tasks, each subject was presented tachistoscopically with three sets of transcriptional stimuli, i.e., kanji, katakana, and hiragana stimuli, arranged in random order. Three subsessions were conducted with different exposure durations, 1/10 second (Task 1), 1/2 second (Task 2), and 1 second (Task 3), respectively. In the writing tasks, each patient was required to write the word for each of 20 different pictures presented (Task 4) and also to write the words to dictation (Task 5), using both kanji and hiragana (for the 10 non-imported words) or katakana only (for the 10 imported words). The results showed that 1) the performance levels of aphasics subjects in all tasks were significantly lower than those of non-aphasic subjects, 2) Group B aphasics (with apraxia of speech) made a significantly greater number of errors in kana processings than in kanji processings in the tachistoscopic tasks (Tasks 1, 2, and 3) as well as in the writing tasks (Tasks 4 and 5), while Group A aphasics (without apraxia of speech) exhibited no such clear difference. On the basis of the findings it was concluded that the selective impairment of kana processing exhibited by the Group B patients is associated not only with the overall severity but with the specific type of the aphasic syndrome of this group, i.e., “apraxia of speech” superimposed on aphasia. Hypotheses concerning the possible underlying mechanisms for this phenomenon are discussed.