Masking versus cognition during speech recognition in noise and reverberation: Can different sentence tests provide a quantitative estimate?

This study investigates the effect of noise and reverberation on speech recognition for an open- and a closed-set sentence test. While both tests yield approximately the same recognition threshold in trained normal hearing listeners, their performance may differ due to cognitive factors, i.e., the closed-set test is more sensitive to training effects while the open-set test is more affected by language familiarity. The experimental data were compared to predictions of the speech transmission index as a measure of pure acoustic effects. The largest differences between the open- and closed-set speech tests were measured in reverberation indicating a considerable influence of non-acoustic, cognitive factors. The recognition scores were on average 50% higher for the closed-set test with syntactically fixed and semantically unpredictable sentences than for the open-set test consisting of everyday sentences. To examine the underlying reasons, the closed-set test was presented to naïve listeners, with no training prior the measurements and no information about the test's structure. Removing this information, the differences between the tests were not present indicating that the degree of familiarity with the speech material has a major impact on speech recognition. This indicates a strong cognitive factor which cannot be predicted by the speech transmission index.