Estimating the transition bandwidth between two auditory processes: evidence for broadband auditory filters

A spectral discrimination task was used to estimate the frequency range over which information about the temporal envelope is consolidated. The standard consisted of n equal intensity, random phase sinusoids, symmetrically placed around a signal component. The signal was an intensity increment of the central sinusoid, which on average was 1000 Hz. Pitch cues were degraded by randomly selecting the center frequency of the complex and single channel energy cues were degraded with a roving-level procedure. Stimulus bandwidth was controlled by varying the number of tones and the frequency separation between tones. For a fixed frequency separation, thresholds increased as n increased until a certain bandwidth was reached, beyond which thresholds decreased. This discontinuity in threshold functions suggests that different auditory processes predominate at different bandwidths, presumably an envelope analysis at bandwidths less than the breakpoint and across channel level comparisons for wider stimulus bandwidths. Estimates of the "transition bandwidth" for 46 listeners ranged from 100 to 1250 Hz. The results are consistent with a peripheral filtering system having multiple filterbanks.