Falling vocal intonation signals speaker confidence and conditionally boosts persuasion

People are often advised to project confidence with their bodies and voices to convince others. Prior research has focused on the high and low thinking processes through which vocal confidence signals (e.g., fast speed, falling intonation, low pitch) can influence attitude change. In contrast, this research examines how the vocal confidence of speakers operates under more moderate elaboration levels, revealing that falling intonation only benefits persuasion under certain circumstances. In three experiments, we show that falling (vs. rising) vocal intonation at the ends of sentences can signal speaker confidence. Under moderate elaboration conditions, falling (vs. rising) vocal intonation increased message processing, bolstering the benefit of strong over weak messages, increasing the proportion of message-relevant thoughts, and increasing thought-attitude correspondence. In sum, the present work examined an unstudied role of vocal confidence in guiding persuasion, revealing new processes by which vocal signals increase or fail to increase persuasion.