Speech intelligibility as a function of time compression, age, word position, and signal-to-noise ratio
Abstract
Among other parameters, speech intelligibility depends on the rate of speech. Therefore, variation of time compression might be useful for adjusting the threshold of 50% intelligibility in speech in noise tests at fixed positive signal-to-noise ratios (SNRs). Speech rate can be modified with uniform and non-uniform algorithms. Uniform algorithms delete equally spaced segments, while non-uniform algorithms first characterize the structure of the speech and then increase the speech rate dependent on the classification. Referring to studies using fast speech, age effects have to be taken into account. To investigate fast speech in a German speech intelligibility test, sentences speeded to different time compressions were presented at different SNRs and intelligibility measurements were conducted with young and elderly normal-hearing listeners. The outcomes were used to calculate SNR-dependent discrimination functions. The results showed increasing SNRs for 50% intelligibility with increasing time compression. As expected, young listeners reached higher intelligibility than elderly listeners at equal time compressions and SNRs for 50% intelligibility were shifted to lower values. Additionally, increasing the speech rate affected word intelligibility in dependence on the words’ position within the sentences. These differences in intelligibility led to shallower slopes of the discrimination functions and could possibly constrain the accuracy of the test.
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