Effects of temporary thershold shift on combination-tone generation and on two-tone suppression

Two-tone suppression and combination tone generation (2f1 - f2) are two phenomena that can be described by a single cochlear nonlinearity. Both phenomena are affected by a permanent threshold shift, which supports the idea of a common origin. In the present experiment the effect of a temporary threshold shift (TTS) on both phenomena is investigated. A clear effect of TTS on combination tone level and phase was found, but no effect on two-tone suppression. Limited data and small TTS require caution when the results are interpreted. Tentatively, the results contradict the common-origin concept. The (reversible) effect of TTS on the combination tone demonstrates that the combination tone is not simply due to nonlinear basilar membrane mechanics, but that a sensorineural process is involved.