Oscillations, Waves, and Interactions - GWDG

Specific signal types in hearing research 45
Figure 5. Responses of a linear,
fourth-order gamma-tone model at resonance
frequency 1100 Hz to the three
harmonic maskers with fundamental
frequency 100 Hz shown in Fig. 1. The
top panel shows the zero-phase signal,
the middle panel the negative
Schroeder-phase and the bottom panel
the positive Schroeder-phase complex.
Reused with permission from Ref. [9].
Copyright 1995, Acoustical Society of
America.
characteristic relative to its resonance frequency. The curvature of the filter phase
changes its sign at the resonance frequency from negative to positive. A filter with
such a phase characteristic can never flatten out the phase of a Schroeder-phase
complex over the full range of its passband.
2.1.4 Later developments
Although the first paper on Schroeder-phase stimuli was already published in 1986 [15],
the paradigm was only widely adopted after publication of our second paper in
1995 [9]. The first papers that used the term “Schroeder phase” in their title were
published in 1997 [20,21]. Many authors related psychoacoustic findings with Schroeder-phase
stimuli to the properties of the basilar membrane. Differences that were
found between normal-hearing and hearing-impaired subjects and also influences of
the overall presentation level indicated some role of active processes in creating large
differences between positive and negative Schroeder-phase stimuli [21–23]. Based on
the results of these studies, Summers concluded: “The current results showed large
differences in the effectiveness of positive and negative Schroeder-phase maskers under
test conditions associated with nonlinear cochlear processing. The two maskers
were more nearly equal in effectiveness for conditions associated with more linear pro-