Modeling auditory processing of amplitude modulation

In this thesis a new modeling approach is developed which is able to predict human performance in a variety of experimental conditions related to modulation detection and modulation masking. Envelope uctuations are analyzed with a modulation lterbank. The parameters of the lterbank were adjusted to allow the model to account for modulation detection and modulation masking data with narrowband carriers at a high center frequency. In the range 0-10 Hz, the modulation lters have a constant bandwidth of 5 Hz. Between 10 and 1000 Hz a logarithmic scaling with a constant Q-value of 2 is assumed. This leads to the following predictions: For conditions in which the modulation frequency (fmod) is smaller than half the bandwidth of the carrier ( f), the model predicts an increase in modulation thresholds with increasing modulation frequency. This prediction agrees with the lowpass characteristic in the temporal modulation transfer function (TMTF) in the literature. Within the model this lowpass characteristic is caused by the logarithmic scaling of the modulation lter bandwidth. In conditions with fmod > f 2 , the model can account for the highpass characteristic in the threshold function, re ecting the auditory system's frequency selectivity for modulation. In modulation detection conditions with carrier bandwidths larger than a critical band, the modulation analysis is performed in parallel within each excited peripheral channel. In the detection stage of the model, the outputs of all modulation lters from all excited peripheral channels are combined linearly and with optimal weights. The model accounts for the ndings that, (i), the \time constants" associated with the temporal modulation transfer functions (TMTFs) for bandlimited noise carriers do not vary with carrier center frequency and that, (ii), the time constants associated with the TMTF's decrease monotonically with increasing carrier bandwidth. The model also accounts for data of modulation masking with broadband noise carriers. The predicted masking pattern produced by a narrowband noise along the modulation frequency scale is in very good agreement with results from the literature. To integrate information across time, a \multiple-look" strategy is realized within the detection stage. This strategy allows the model to account for long time constants derived from the data on modulation integration without introducing true long-term integration. Instead, the long \e ective" time constants result from the combination of information from di erent \looks" via multiple sampling and probability summation. In modulation detection experiments with deterministic carriers (such as sinusoids), the limiting factor for detecting modulation within the model is the internal noise that is added as independent noise to the output of all modulation lters in all peripheral lters. In addition, the shape of the peripheral lters plays a major role in stimulus conditions where the detection is based on the \audibility" of the spectral sidebands of the modulation. The model can account for the observed at modulation detection thresholds up to a modulation rate of about 100 Hz and also for the frequency-dependent roll-o in the threshold function observed in the data for a set of carrier frequencies in the range from 2{9 kHz. The model might also be used in applications such as psychoacoustical experiments with hearing-impaired listeners, speech intelligibility and speech quality predictions.