Average discharge rate of single auditory-nerve fibers in cats was measured in response to one- and two-tone stimuli. One component (the “suppressor tone”) of each two-tone stimulus was at a frequency (f2) which produced two-tone suppression at some stimulus levels. The other component (excitor tone) produced an increase in rate above the spontaneous rate when presented alone. Fractional response was defined as the driven rate to the two-tone stimulus divided by the driven rate to the excitor presented alone. Fractional response is thus a quantitative measure of the amount of suppression produced by a suppressór tone. A number of qualitative differences were found in the dependence of fractional response for f2> CF and f2< CF. For suppressor tone frequencies greater than CF, fractional response depends only on the ratio of suppressor to excitor levels (P2/P1) for a range of excitor levels (P1). For P1large enough to drive a unit into saturation, fractional response increases with P1. For f2< CF, however, fractional response is a monotonic decreasing function of P2and P2/P1; it is also a monotonic decreasing function of P1for P2/P1fixed. Consistent with these results if the tone level ratio P2/P1is fixed, rate is a monotonic increasing function of the overall level of a two-tone stimulus for f2> CF; for f2< CF, rate is typically a nonmonotonic function of overall level. For f2> CF, slopes of (log) fractional response versus (log) P2/P1curves are a monotonic decreasing function of suppressor frequency f2. For f2< CF, on the other hand, slope does not depend on f2. If f2is fixed, and excitor-tone frequency (f1) varied, fractional response decreases with f1for f2>CF; for f2<CF, fractional response is independent of f1.
ASJC Scopus subject areas
- Arts and Humanities (miscellaneous)
- Acoustics and Ultrasonics