Sharpening of the Signal Spectrum Contrast as a Result of Lateral Suppression in the Human Auditory System.

The spectrum contrast threshold for the comb-filtered signal was measured at various ripple densities in listeners with normal hearing. The lowest spectrum contrast thresholds of less than 0.1 appeared at a ripple density of 3-4 oct. With the ripple density falling down to 1 oct, the threshold increased to 0.17. At the ripple density higher than 4 oct, the threshold was also growing to achieve 1.0 at a density of 7-8 oct. An increase of threshold at high ripple densities can be explained by integration within critical bands. At low ripple densities, the threshold increase may be a result of the lateral suppression that led to sharpening of the spectral contrast.