CLINICAL STUDY OF TIME-SHIFT EVOKED POTENTIALS

Abstract

Changing the interaural time difference (ITD) of continuous band noise applied to both ears causes a shift in the perceived lateralization of the noise and evokes the special potentials called "time-shift evoked potentials (TPEPs)". These potentials consist of a positive-negative-positive complex, like a slow vertical response (SVR). Each peak latency of this potential, however, was about 20 msec longer than in the SVR. Testing of 45 volunteers with normal hearing revealed that the feature of this response matched the hearing function test results of detecting lateral position of a sound image. Therefore it could be useful as an objective testing for the hearing function of sound latelization. The following were established as the conditions for use, in clinical practice: time difference between ears: 0.7 msec; sound intensity: 30 dB SL at 500-Hz band noise; stimulus interval: 3.0 sec.; and potential recording from Cz on the scalp. This response was tested in 29 cases of hearing disorders (14 cases of inner ear deafness, 2 cases of tinnitus without deafness, 6 cases of peripheral vertigo, 5 cases of intracranial disease, 1 case of functional hearing loss, 1 case of head trauma), and the results were compared with those of the directional hearing test, auditory brainstem response (ABR), and SVR, by using the chi-square test. The results of the directional hearing test and ABR were shown to be correlated with this ERP, and SVR was shown to be independent of it. Thus, it was concluded that this potential is useful as a clinical test. The significance of the conclusions is explained on the basis of Berjeik's theory.