In recent years non-simultaneous masking methods were used in many psychoacoustical investigations. In particular, the forward-masking paradigm proves to be of great advantage concerning the temporal and spectral selectivity of the ear. Comparable results of neurophysiological investigations of forward-masking conditions were obtained at the level of auditory nerve (Smith 1977, Bauer 1978, Harris and Dallos 1979). Smith (1977) and Harris and Dallos (1979) concluded that there exists a reciprocal relationship between the poststimulatory recovery and the stimulatory adaptation; that both processes are directly related to the level of excitation; and that the two processes are independent of stimulus parameters. Bauer (1978), however, could demonstrate in some cases a dependence of poststimulatory “fibre-masking functions” on stimulus parameters, pointing to the poststimulatory influence of two-tone suppression.