Growth of pulsation threshold of a suppressed tone as a function of its level

The pulsation threshold (PT) was measured at the frequency of a probe tone in a two-tone stimulus. A suppressor tone was higher in frequency than the probe tone and was fixed in level. As the level of the probe tone was increased, three regions of performance were observed: (1) for probe tone levels below simultaneous masked threshold (SMT), PT was the same as that measured for the suppressor alone, (2) for levels above SMT, PT increased linearly with level, indicating a constant amount of suppression in dB, and (3) for higher levels a recruitment-like phenomenon was observed, in which the PT increased faster than the probe level. The maximum amount of suppression observed was equal to the difference between the PT and SMT for the suppressor alone. One interpretation is that the suppressor reduces excitation on the slopes of its own excitation pattern by the same amount that it reduces the additional excitation from a probe tone. These results are consistent with physiological data, where the amount of suppression is determined by the suppressor and is independent of the level of the probe tone.