Oscillations, Waves, and Interactions - GWDG

Specific signal types in hearing research 59
Figure 14. The two panels show experimental data for modulation detection (left) and the
prediction of the modulation filterbank model developed in Ref. [36] (right). The symbols
indicate the three different noise types. GN: Gaussian noise; MN: multiplied noise; LNN:
low-noise noise. Reused with permission from Ref. [41]. Copyright 1999, Acoustical Society
of America.
frequencies, while thresholds decrease for these two carrier types towards modulation
frequencies corresponding to the carrier bandwidth of 50 Hz. In this range, thresholds
for multiplied noise are clearly lower, which is in line with the analysis of the envelope
spectra shown in Fig. 12. In contrast, the thresholds for low-noise noise are very
low at the lowest modulation frequencies and increase towards 50 Hz. This increase
directly resembles the increase in envelope power up to 50 Hz shown in Fig. 12.
The right panel shows the prediction of the modulation filterbank model that was
originally developed for prediction of data obtained with Gaussian noise only [36,47].
The resemblance between data and model prediction is strong evidence that the
basic ideas incorporated in the model capture properties of the hearing process in an
appropriate way.
The last example for the potential of multiplied noise comes from binaural hearing.
These experiments are based on the phase-locked interaction between masker and
test signal and the possibility to create masking conditions with differences only
in interaural time, or interaural level. These experiments will be discussed in the
following section which focusses on binaural experiments.
4 Stimuli for research on binaural hearing
One of the main areas of psychoacoustic research at the DPI was binaural hearing, in
which the particular consequences of differences between the acoustic waveforms at
the two ears are studied. Binaural hearing addresses issues such as localization and
lateralization of stimuli, and the wide area of binaural unmasking, the ability to detect
a source in the presence of other background sources with the same or different spatial
parameters. Binaural hearing requires that the signals from both ears are, somewhere
in the hearing pathway, compared for coincidences and differences. Because such an
interaction only takes place in neural centers far beyond the inner ear, it is very hard
to directly test models of binaural hearing. Therefore, the interplay between models
and the design of critical experiments is of particular relevance for advancing the
understanding of human hearing in this area.