A nonlinear model of the basilar membrane (BM) is examined for the two-tone suppression (TTS). The authors tested the BM displacement, velocity and acceleration as a possible candidate of the stimulus to the hair cell. Only in the BM acceleration TTS was observed, that has quite similar tendencies to physiological data.

Multiple Markov sequences of interpoint intervals are generated by computer simulation. A kind of rational transition probability density function presented here is found to be satisfactory to simulate wide varieties of neuronal spike trains. Three examples of the Markov sequences are examined and investigated from a viewpoint of point density, two of which are to simulate the actual spike trains obtained from the central neurons of the cat. The third one has exponential type interval histogram. The generated Markov sequences as well as the neuronal spike trains usually show slow fluctuations of point densities. When a point sequence of this kind is smoothed by an appropriate filter, the approximate point density fluctuation is extracted. By an inverse procedure of integral density modulation with this point density as the modulating signal, the point sequence is transformed into another sequence of which the slow component of point density is eliminated. It is found that the transformed point sequence can be approximately regarded as a non-correlative sequence, if a right kind of filter is selected. This shows that both the simulated Markov sequences and the neuronal sequences tested here are almost regarded as the density modulated point sequences of the non-correlative sequences of intervals.

A nonlinear electric circuit model of the whole length basilar membrane (BM) of the human is constructed. It is of transmission analogue type. Nonlinearity is introduced into its loss factors, using resistors and Ge diodes. By observing the membrane velocity of the model, we examine: (i) response to combination tones (CT) with two primary tones of frequency fL, fH and level LL, LH (fLfH), (ii) 2fLfH CT cancellation characteristics, (iii) two-tone wuppression and (iv) other responses. Suppressed tone has frequency f1(characteristic frequency (CF) of given section) and level L1, and suppressor tone has frequency f2 and level L2. Distribution of 2fLfH CT component shows that at some sections it cominates the primaries in amplitude, while 2fHfL component is very much smaller all along the model. The 2fLfH CT distribution patterns in the model, when it is cancelled, seem to indicate good correspondence with the psychophysical cancellation. Three CT cansellation characteristics (LLLH varied, LL varied, fH varied) show good agreement with psychophysical experiments, including the nonmonotonic behavior of the CT. It seems to be possible to have more agreement by using sharper tuning property and stronger nonlinearity. For frequency f1f2, average value of BM velocity shows two-tone suppression, but for f2f1, it shows a little suppression. It will be worthwhile to consider other variables, such as BM displacement or acceleration, as model output.