抄録
A clinical significance of the objective testing method available for the orientation of the dominant cerebral hemisphere for speech using key tapping (Tsunoda) was explained in detail. The author compared the findings obtained by the tapping method with those obtained by the Wada technique, and he strongly stressed that the side of the dominant cerebral hemisphere for vowel sounds (ah, uh, eh) coincided with one for speech. In order to find the reasons why the human vowels are dominantly processed in the dominant cerebral hemisphere for speech, the following experiments on normal subjects were carried out. Eight hundred and fifty Hz low pass vowel Uh that contained only F1 but excluded beyond F2 was applied to the test and qualitative shift to the nondominant cerebral hemisphere was found.
When filter ed vowel sound that contained F1 and F2 was applied to the test, the right ear (left cerebral hemisphere) dominancy was observed. Four times accelerated vowel Ah and Uh in reproduction speed were also applied to the test, and the result was similar to that for normal speed vowels. FM sounds (ascending, descending), AM sounds and amplitude modulated FM sounds were also confirmed to be dominantly processed in the non-dominant cerebral hemisphere. Finally, the complex sounds consisting of more than two combination of narrow band noises were applied to the test. When the frequency ratio of F2/F1 was inharmonic relation, the right ear dominancy was observed, whereas when the ratio F2/F1 was harmonic the left ear dominancy was observed. From the standpoint of dominancy effect, the author classifies the human cerebral hemispheres into two categories such as inharmonic brain and harmonic brain. Above mentioned results do not coincide with results of the Haskins laboratory.
