Abstract: Vocal attractiveness plays an important role in social interaction. Different levels of vocal attractiveness could convey different information. Previous studies found that the speakers with attractive voices got more positive social evaluation. This phenomenon is similar to the "beauty premium" which was reported by vast research about facial attractiveness. In addition, both attractive voices and attractive faces can activate the reward system of brain. Many studies revealed that face attractiveness can influence decision-making. For example, in the ultimatum game, attractive faces increased the acceptance ratio of offers compared with the unattractive-face condition. However, it is not clear whether vocal attractiveness can also impact decision-making. The present research adopted a two-person ultimatum game (Experiment 1) and a three-person ultimatum game (Experiment 2) to examine the effect of vocal attractiveness of a male proposer and the effect of vocal attractiveness of a powerless male third player on decision-making.
32 male voices (16 attractive voices, 16 unattractive voices) were selected before the formal experiments as the stimuli. In Experiment 1, 50 participants (36 females, 14 males) were recruited to participate in a two-person ultimatum game. In each trial, a voice of the proposer was presented first. Then, the proposer's offer to split ¥10 between himself and the participant was displayed on the screen. As a responder, each participant had to decide whether to accept the offer. If the offer was accepted, the money would be divided as proposed. Otherwise, both the proposer and the participant got nothing. In Experiment 2, 40 participants were recruited (20 males, 20 females) to participate in a three-person ultimatum game, which included a proposer, a responder (the participant) and a powerless third player. A voice of a powerless third player was presented first. Then, an allocation of how to split ¥12 among the three players was shown on the screen. The participants had to decide whether to accept the offer after thoroughly thinking not only for themselves but also for the powerless third player. If the offer was accepted, the money would be divided as proposed. If not, all players got nothing.
The results of Experiment 1 showed that the unfair offers from the proposers with attractive voices were more likely to be accepted, comparing with those from the proposers with unattractive voices. However, the acceptance ratio of fair offers was not affected by vocal attractiveness. The acceptance ratio of fair offers was greater than the acceptance ratio of unfair offers. Consistent with Experiment 1, the results of Experiment 2 showed the acceptance ratio of “fair/fair” offer was significantly higher than the other three offers. The acceptance ratio of “unfair/unfair” offer was significantly lower than the other three offers. There was no significant difference between the “fair/unfair” offers and the “unfair/fair” offers. More importantly, in the “unfair/fair” offer condition in which participants received a smaller allocation than the third player, the acceptance ratio was higher when the third player had an attractive-voice.
In conclusion, vocal attractiveness of the proposers modulated the acceptance ratio of unfair offers in the two-person ultimatum game. Moreover, in the three-person ultimatum game, vocal attractiveness of a powerless third player modulated the acceptance ratio of offers in which the participants got less money than the third player, suggesting that attractive voice increased the participants' altruism towards the third player. Our findings provided evidence that the "beauty premium" phenomenon also exists in vocal attractiveness. It is easier for people with attractive voice to get economic reward in social interaction. Vocal attractiveness can modulate the participants' fairness consideration and reduce the participants' aversion to inequality.

Key words: ultimatum game, vocal attractiveness, fairness, beauty premium