A framework for studying causal effects of speech style: application to US presidential campaigns
本文指出仅分析文本会带来偏差，并提出了一个考虑言语多模态特性的因果框架，通过美国总统竞选演讲的实例，展示了两种更可靠的实验设计来估计言语风格的因果效应。
Abstract Numerous disciplines hypothesize about the causal effects of speech, which influences others not only through which words are spoken, but also how they are spoken. Yet applied research focuses almost exclusively on the textual component of speech—ignoring audiovisual components or reducing them to coarse summary statistics. We show that text-only analyses are biased, except in implausible scenarios where (a) non-textual speech elements are irrelevant to listeners, or (b) speakers’ vocal style does not change with the words spoken. Even analyses including audiovisual summary measures are biased unless (c) these measures satisfy a ‘sufficient reduction’ condition, fully capturing the non-textual mechanisms through which speech operates. To demonstrate, we develop a formal causal framework that accounts for the unstructured and multimodal nature of speech. We present an application to US presidential campaign speeches, using the framework to clarify implicit assumptions in prior work. We then demonstrate two designs that permit valid hypothesis tests and causal effect estimates under more plausible conditions: (1) a naturalistic experiment exploiting subtle variation in campaign speech ‘catchphrases’ with near-identical wording, identified with automated phrase-clustering methods; and (2) an audio conjoint experiment with nearly 1,000 recordings manipulating specific vocal mechanisms, produced with professional voice actors and audio-editing software.