The psychological link between decisions and communicative behavior based on verbal probabilities

Verbal probability is categorized into two types in terms of directionality: positive (suggesting the occurrence of a target outcome: e.g., "it is likely") or negative (suggesting the nonoccurrence: e.g., "it is quite uncertain"). Previous studies have shown that people's decisions are affected by differences in directionality, and that they use either positive or negative expressions depending on the communicative situation. In this study, we attempt to clarify the relationship between decisions and communicative behavior based on verbal probabilities. We proposed a quantitative model called Decision by Belief Sampling based on the Decision by Sampling model and the reference point hypothesis, and examined whether decisions and communicative behaviors could be explained with this model. The proposed model reveals the psychological mechanisms underlying superficially unrelated phenomena between decisions and communicative behaviors. In particular, listeners of verbal probabilities (decision-makers) infer the beliefs held by a speaker (conveyer of information) and make decisions based on these beliefs. These inferred beliefs align with the speaker's beliefs when communicating probabilistic information. Thus, the proposed model clarifies the psychological link between decisions affected by directionality and communicative behaviors (speaker's choice of directionality).