[The objective frequency decrement test (OFDT): a new objective EEG-test for determination of the difference limen for frequencies (author's transl)].

Abstract

Subjective methods measuring the difference limen for frequencies (DLF) take a lot of time and are not reliable. You can find this fact not only while testing normal subjects, but also while testing patients with hearing loss combined with tinnitus. Therefore this new objective DLF-test has been developed. Apart from the testing function for clinical purpose, the different results of other studies can also be controlled. After 1080 msec a pure tone is changed to a lower frequency for a period of 670 msec. Immediately after the tone is finished a picture is presented. As a control pure tones of unvarying pitch are offered. This stimulus sequence is repeated for several times. The expectancies to the change of pitch and to the picture produce a negative slow potential shift (Walter's CNV) in the EEG. The perception of frequency change yields to a late evoked potential and to a DC-shift; as a result of the optimum conditions of the expectancy-situation and the appropriate recording-technique only 5-10 sweeps must be summed up to obtain a potential, sometimes it even can be seen in the "raw-EEG". The test makes a differentiation between a just believed and a real perception possible. A sample of subjects with normal hearing and a subgroup (musicians) were selected for the standardization. Because of objectivity, reliability and economy the test can be used for clinical application.