Abstract:

NoS(pi) thresholds were measured using a 3IFC paradigm for masker levels between 10 and 80 dB SPL. Three types of narrow-band maskers were used to investigate the influence of the envelope probability distribution on signal detectability. The three types were multiplied noise (MN), Gaussian noise (GN), and low-noise noise (LNN) each with a bandwidth of 25 Hz. Due to the rather low NoSo thresholds for LNN, both monaural and binaural detection cues might be used by subjects in the NoS(pi) condition. In order to avoid this, for LNN maskers, an NoSo stimulus was presented in the reference intervals at the same signal-to-noise ratio as in the NoS(pi) test interval. The results show that at medium levels (40--70 dB), thresholds in MN are about 10 dB lower than for the other maskers. This difference decreases or even disappears at low and high levels. It is proposed that these effects are related to the compressive transformations which occur in the cochlea. These transformations decrease the size of the interaural intensity differences present in the envelopes of the maskers, and can be shown to do so more effectively for GN and LNN maskers than for MN maskers.