Proceedings of the Annual Meeting of the Cognitive Science Society

We examined decisions based on verbal probability phrases,such as "small chance," "likely," or "doubtful" (we call thesephrases verbal probabilities). Verbal probabilities havecommunicative functions called directionality and can becategorized into positive (e.g., "likely" or "probable") ornegative (e.g., “unlikely,” “doubtful”) phrases in terms oftheir directionality. Previous studies have shown that thedirectionality of phrases affects decisions. Although suchdecisions seem biased, we argue that they are not. Wehypothesize that since a speaker has the option to choose thedirectionality used during communication, the selecteddirectionality becomes relevant information to a decisionmaker, and is taken into account in making decisions. Wemodeled these processes using the Decision by BeliefSampling (DbBS) model. We found that the observed datacould be well explained by our hypothesis, and that the DbBSmodel could be one of the best potential models for decisionsbased on verbal probability information.