Lateral suppression enhances discrimination of comb-filtered signals

Spectrum contrast thresholds were measured in normal-hearing listeners using comb-filtered signals. The signal spectrum contained 0.075-oct wide ripples of varying depths. The ripple depth thresholds were measured at ripple densities from 1 to 7/oct using a two-alternative forced-choice adaptive procedure. The lowest ripple depth thresholds of less than 0.1 appeared at a ripple density of 3 to 4/oct. At lower ripple densities down to 1/oct, the thresholds increased up to 0.2. At ripple densities above 4/oct, the thresholds steeply increased up to 1.0 at densities of 7/oct. Based on the excitation-pattern model, the threshold increase at high ripple densities may be explained by integration within the passbands of the frequency-tuned filter. A threshold increase at low ripple densities cannot be explained by a simple bandpass filter model. The lowest spectrum contrast thresholds at intermediate ripple spacing indicate the presence of lateral suppression zones in the equivalent filter forms. According to th...