Figure 1: Schematic representation of the spectral envelopes of the two promels. The envelopes have peaks at frequencies f11 and f12 which, from trial to trial and according to the adaptive procedure, change simultaneously and in opposite directions, i.e., the quantity f1=f12-f11 is the dependent variable of the experiment. The envelopes have a fall-off of 3 dB/oct on either side of the peaks. The envelopes cover series of seven sinusoidal components separated by one of two fundamental frequencies f01 and f02 , starting at harmonic numbers m or n , respectively; neither m nor n must be integer numbers, that is, either one or both promels may be inharmonic.

Figure 2: Schematic representation of the spectral envelopes of the two promels. The envelopes have peaks at frequencies f11 and f12 which, from trial to trial and according to the adaptive procedure, change simultaneously and in opposite directions, i.e., the quantity f1=f12-f11 is the dependent variable of the experiment. The envelopes have a fall-off of 3 dB/oct on either side of the peaks. The envelopes cover series of seven sinusoidal components separated by one of two fundamental frequencies f01 and f02 , starting at harmonic numbers m or n , respectively; neither m nor n must be integer numbers, that is, either one or both promels may be inharmonic.