A Trade-off Relationship between Lexical and Prosodic Means in Expressing Subjective and Objective Causality

Prosody carries a variety of information in spoken communication. However, how it is involved in expressing the structure of discourse remains less well understood. This study addressed this issue by investigating the use of prosody in expressing two types of causality: subjective and objective causality. Specifically, we explored a trade-off relationship between prosody and lexical means, i.e., specialized causal connectives. We hypothesized, based on several theories, that the prosodic distinctions between subjective and objective causality would be less salient when the two types of causality are expressed by specialized causal connectives (e.g., kejian (so) and yushi (so) in Mandarin) than by a general causal connective (e.g., so in English). We conducted two production experiments to test this hypothesis, with Experiment 1 investigating the prosodic realizations of subjective and objective causality in English and Experiment 2 in Mandarin. We used a self-designed dialogue task to elicit speech samples and adopted a Bayesian approach to evaluate the effects of subjectivity on several acoustic measurements. The results of these two experiments support our hypothesis.