Pitch accent disorder observed in a Japanese patient due to traumatic head injury

要旨

Background Suprasegmental features are often affected by brain damage, and are typically accompanied by motor speech disorders such as dysarthria, apraxia of speech (AOS), and foreign accent syndrome (FAS). However, there is no report of a selective pitch accent disorder without motor speech impairments or FAS.Aims We describe a female Japanese patient who developed a selective pitch accent disorder without motor speech impairments or FAS, with accompanying mild Wernicke’s aphasia due to head injury, in order to investigate the mechanism of pitch accent disorder based on speech production models.Methods & Procedures We analysed her spontaneous speech, confrontation naming, repetition, reading aloud, and the error patterns in her pitch accents in two sessions. Additionally, we gave her a reading aloud test of homonyms with different accent patterns and an auditory discrimination task of pitch accents.Outcomes & Results The patient exhibited a significant recovery from aphasia, and paraphasia was observed to almost disappear, although the pitch accent errors remained in all speech modalities. While she was able to auditorily distinguish between correct and incorrect pitch accents, she was unaware of her own abnormally accented speech. The results of the analysis of the error patterns in her pitch accents revealed that they, even if incorrect for the selected words, did not actually deviate from the correct patterns in the Osaka dialect, her native dialect.Conclusions Our observations suggest that the process of pitch accent production may be independent of that of phoneme production. Moreover, it may be that her accent abnormalities were not produced randomly during the process of articulation, but instead may have been due to a problem in selecting pitch accent patterns from the repertoire of Osaka accent patterns allocated to the corresponding words. This suggests that the patient’s pitch accent disorder was a problem in a higher level of linguistic processing, i.e., lexical pitch accent encoding, rather than the motor control of speech production.

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