Analysis of the clinical symptoms of 27 cases of buccofacial apraxia (oral apraxia) due to left hemisphere lesion revealed that types of error response differed depending on the category of the movements which the patient gesticulated. Specifically, vocal overflows were significant when the patients performed movements related to respiration (e. g., puffing and throat clearing), while parapraxias were characteristic of movements related to eating (e. g., biting and swallowing). Error responses also differed depending on the type of aphasia. Vocal overflows were characteristic of motor aphasia, while parapraxias were significant in sensory aphasia and anomic aphasia. It was also revealed that both the complication of severe buccofacial apraxia and apraxia of speech, and the complication of severe buccofacial apraxia and disturbance of auditory phonemic comprehension (phonemic decoding), affect the articulation of the patient. Comparison of the lesional localization of cases with buccofacial apraxia and cases without buccofacial apraxia after the left hemisphere lesion revealed that the lesion responsible for buccofacial apraxia was located between the infero-anterior portion of the left supramarginal gyrus and the infero-posterior portion of the left posterior central gyrus. Within the left inferior parietal lobule, the level of the lesion of buccofacial apraxia was inferior to that of limb apraxia. Buccofacial apraxia and limb apraxia seemed either to derive independently or to complicate according to the level of the lesion in the left parietal lobe; as a result, the neural information processing mechanisms underlying these apraxias may be fundamentally identical. A theory based on behaviorism to explain both the mechanism of generation and variation of apraxias was presented.

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