Masking effects of speech and music: Does the hierarchical structure of the masker matter

1.1 Objective. Speech and music are time-varying signals organized by hierarchical rules. Growing bodies of evidence also show that music is processed in primary speech/language-processing cortical regions (Levitin & Menon, 2003). Therefore, music can be a serious competing signal to speech. This study compared the masking effects of single-talker speech and instrumental music with variable hierarchical rules on listeners' perception of sentences.;1.2 Design. This study was comprised of two experiments. Experiment 1 included 21 listeners (10 musicians, 11 non-musicians) and Experiment 2 included 26 listeners (10 musicians and 16 non-musicians). Both experiments were designed to measure listeners' perception of sentences presented with various maskers. The target signals were presented at 39 dB HL and the signal to noise ratio was -6 dB HL. In Experiment 1, listeners were presented with TREE sentences in four masking conditions: original speech, original music, scrambled speech, and scrambled music. Scrambled maskers were hierarchically disrupted using a technique similar to that of Levitin and Menon (2003). In Experiment 2, six maskers were presented: three excerpts of music of different hierarchical structures and their scrambled counterparts.;1.3 Results. In Experiment 1, listeners performed better with music masker than with speech masker. They also performed better when these maskers were hierarchically intact than disrupted. In Experiment 2, different music maskers resulted in different levels of performance. In addition, listeners' performance varied depending on whether the hierarchical structure of different music maskers was intact or disrupted. Listeners' music training or their familiarity with the music maskers did not significantly affect their speech perception in either speech or music maskers.;1.4 Conclusions. The presence of hierarchical structure in the maskers seems to affect their masking potential. This effect can be seen when comparing music maskers across genres (with different hierarchical structures) and when comparing music maskers before and after their hierarchical structure is purposefully disrupted. No difference was found between the performances of musicians and non-musicians in speech/language perception in music maskers.