Effects of stimulus frequency on two-tone suppression: A comparison of physiological and psychophysical results

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Abstract
The effects of stimulus frequency on 2-tone suppression were investigated in single auditory-nerve fibers of anesthetized cats and compared with human psychophysical data. In the physiological experiment, both average discharge rate and phase-locked activity were measured in response to 1- and 2-tone stimuli. The 1st component f1 produced an increase in rate above spontaneous activity when presented alone. The 2nd tone f2 was always well below the fiber''s characteristic frequency and was held at a fixed sound pressure level appropriate to produce 2-tone suppression. Responses were plotted as a function of stimulus level of the 1st tone both alone and in the presence of f2. For different values of f1 with f2 fixed, suppression was maximum with f1 near fiber CF [characteristic frequency]. In the psychophysical experiment, similar stimulus parameters of f1 and f2 were used as the masker in a forward-masker paradigm. The addition of the 2nd masker tone at frequency f2 could produce less masking of the signal. When f1 was varied with f2 fixed, the relative decrease in masking, analogous to suppression, was greatest when f1 was equal to the signal frequency.

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