Parametric studies of tinnitus masking and residual inhibition.

A study was made of the relation between tinnitus masker composition (frequency, bandwidth, intensity duration) and the time course and magnitude of residual inhibition (RI). RI was determined by methods of (a) loudness estimation - where the subject varied the pointer position on a loudness scale (b) loudness balance - where the tinnitus loudness was maintained in loudness balance in the period following masking with a tone of variable intensity presented to the opposite ear. In addition, sensitivity change (temporary threshold shift, TTS) in the tinnitus and masker frequency regions was measured by determining tone thresholds (using a tracking technique) before and after masker presentation. The key findings were as follows: (I) RI depends on masker centre frequency. The frequency producing maximal RI is usually lower than the tinnitus frequency (as determined by pitch matching). (2) In some subjects only narrow-band noise produces RI. (3) RI is proportional to the masker intensity provided the tinnitus is completely masked; little or no RI is produced by a partial masker. (4) For the masker durations used (in the range 10 s to 10 min) RI duration is linearly related to the logarithm of masker duration. (5) A second masker presentation during RI does not potentiate RI. (6) Contralateral masking did not produce RI. (7) maskers producing RI also produce TTS around the tinnitus frequency. (8) The TTS magnitude and the time course of TTS appear to be related to RI.