The effect of modality and speaking style on the discrimination of non-native phonological and phonetic contrasts in noise

Auditory speech is difficult to discern in degraded listening conditions, however the addition of visual speech can improve perception. The Perceptual Assimilation Model [1] suggests that non-native contrasts involving a native phonological difference (two-category assimilation) should be discriminated more accurately than those involving a phonetic goodness-offit difference (category-goodness assimilation), but it is not known whether auditory-visual (AV) benefit is greater for phonological than phonetic differences when the acoustic signal is degraded by speech-shaped-noise. In auditory-only (AO) and AV conditions, monolingual Australian English participants completed AXB discrimination tasks on twocategory versus category-goodness Sindhi contrasts. We also examined the relative influences of phonetic feature difference (laryngeal vs. place-of-articulation [POA]) and speaking style (clear vs. citation speech) on discrimination accuracy. AV benefit was found for POA contrasts, but no effect of speaking style, and AV benefit was larger for two-category than category-goodness contrasts. For laryngeal contrasts, AV benefit was found for the two-category contrasts (across speaking style), but for the category-goodness contrast only when it was clearly articulated. These results indicate that nonnative perceivers use visual speech to their advantage, and to a greater extent for phonological contrasts, but speaking style contributes in AV conditions only for a less salient phonetic contrast.