TONAL FORWARD MASKING: PSYCHOPHYSICAL ESTIMATES OF THE AUDITORY REPRESENTATION OF SOUND SPECTRA OVER TIME
Abstract
The decrease in auditory sensitivity to a tonal probe caused by the prior presentation of a tonal masker was studied. Frequency and level relationships between the masker and probe tones, masker duration and the temporal separation between the two were experimental variables. The results are interpreted in the context of a three-component process, consisting of frequency selectivity, temporal integration of masker energy and recovery from short-term fatigue. Frequency selectivity was found to vary systematically with frequency and level. At high frequencies, selectivity was greatest at low levels and decreased as level was raised. At low frequencies, selectivity was not as good as that at high frequencies but varied little with level. Masked threshold was found to increase as the duration of the masker increased in the forward masking task. An exponential temporal integrator was postulated. The time constants calculated for the exponential functions increased with increasing masker level. Following termination of masker, recovery proceeded linearly in logarithmic time. Recovery functions converged to the same point on the axis regardless of the level of masked threshold. This effect may have been due to the broadening of the residual masking pattern as time delay increased. The experimental results were used to construct a descriptive model of auditory excitation for tonal forward masking. The model had components corresponding to frequency selectivity, temporal integration of masker energy and recovery. Equations were developed to predict the forms of triangular representations of the residual masker and probe excitation patterns. Changes in frequency selectivity were accomplished by varying the slopes of the patterns according to the frequency and level of the masker or probe. The height (magnitude) of the masker pattern was related to masker energy by an increasing exponential function. Recovery during the silent masker-probe interval was represented by collapsing the peak of the masker pattern. Overall, the predictions of the model are comparable with the experimental results and tend to support the characterizations of the hypothetical three-component process.
Degree
Ph.D.
Subject Area
Audiology
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