In this study, we focused on the college-bound deaf population and examined whether deaf college students are more sensitive to unfair information than normal hearing college students in the ultimatum game.
In terms of behavioral outcomes, we only found a significant main effect of offer type. For all subjects, the fairer the proposal, the higher the acceptance rate, which was consistent with previous research whose participates were normal hearing people (Gaechter & Fehr, 2002). Researchers found no difference in social maturity between deaf students and normal hearing college students regardless of whether they wore cochlear implants or not (Marc, Dawn, Kathryn, Georgianna, & Kronenberger, 2018; Marschark et al., 2016). In terms of socioemotional and social behavior, the development of deaf college students and hearing college students may be similar. The results of the deaf college students in this experimental task also support the equity theory rather than the rational person hypothesis (Chang, Levinboim & Maheswaran, 2012; Koenigs, & Tranel, 2007). Deaf college students also have a tendency to be inequity aversion and to punish each other in pursuit of fairness even if they do not gain (Rand, Tarnita, & Nowak, 2013). Moreover, the deaf children and adolescents accepted only milder injustices, with smaller effects (Eichengreen et al.,2020).
EEG results revealed interactions of proposal type and group of N1 components. Further simple effects found that only in the deaf college group, the mean wave amplitude induced by moderately unfair offers and very unfair offers were significantly negative to that of fair offers.We know that the Anterior N1 is the negative component of visual early appearance (~ 100 ms) in the central frontal region (Luck, 1995) which reflects the outcome of early attention, and generally novel or threatening stimuli induce more negative N1 (Ito & Bartholow, 2009; Kubota & Ito, 2007). Our results may show the deaf college students pour more attentional resources into unfair information than normal hearing college students, whether it is a moderately unfair or very unfair offer. According to the differential familiarity hypothesis, the focus on the salient object should also depend on the familiarity of the stimulus, familiarity of a stimulus strongly affects individuals’ visual attention (Jurkat, Köster, Yovsi, & Kärtner, 2020). The deaf college students are more familiar with inequitable information, i.e., inequitable offers (Karampidis, Trigoni, Papadourakis, Christofaki & Escudeiro, 2021). Objectively speaking, the deaf community faces an unfair situation in many ways by not being able to communicate with others in a normal spoken language (Quigley & King, 1980; Soares, Goulart & Chiari, 2010).
In addition to N1, for P2 and P3, we also found main effects of group. P2 is usually found in frontal regions is observed most frequently and is modulated in cognitive tasks involving workload and attentional processes (Merlo et al., 2016). In the target detection paradigm, where targets are distinguished from non-target stimuli by multiple features, target stimuli elicit a significantly larger P2 component than non-target stimuli (Hillyard & Münte, 1984), which may reflect the detection of multidimensional features for processing (Luck & Hillyard, 1994). Fair decision-making involves multidimensional cognition (Barclay, Bashshur & Fortin, 2017; Chernyak, Sandham, Harris, & Cordes, 2016; Sommerville, 2018) and is essentially determined by social cognition and emotion, P3 is thought to reflect attention allocation and motivational salience (Nieuwenhuis, Aston-Jones, & Cohen, 2005; Wu & Zhou, 2009). Based on the results of N1, we conclude that deaf college students may value equity more. The motivational intensity was reduced by the pursuit of benefit for themselves on the one hand and fairness on the other(Turillo et al., 2002). When faced with an event, the motives of deaf people are often diverse. For example, when traveling overseas, deaf people have five driving motives and two pulling motives (Ho & Peng, 2017). In contrast, hearing college students may have pursued the goal of self-benefit more, resulting in a greater intensity of the P3 component than deaf college students for pursuing self-interest(Miller & Ratner, 1996).
Finally, we found the main effect of proposal type is significant, and the more unfair proposal induces a larger FRN amplitude. The FRN component reflects the supervision of fairness, and the more unfair the proposal induces the greater the fluctuation (Alexopoulos, Pfabigan, Lamm, Herbert, & Fischmeister, 2012; Falco, Albinet, Rattat, Paul, & Fabre,2019; Rodrigues, Weiß, Mussel, & Hewig, 2021). The results of FRN show that the FRN is the subject's subjective value judgment of the current event, and a bad event will induce a more negative FRN component. In the ERP study of the ultimatum game, compared with the fair proposal, the unfair proposal is regarded as a bad event, which induced a more negative FRN component. Similar results were found in this study, with deaf college students eliciting a more negative FRN component in the face of unfair offers than fair offers, even when the degree of unfairness was not so deep (3/7, 4 /6).