In summary, results indicated that activation in the ACC varies as a function of resemblance to the participant when individuals are excluded. Activation in the ACC increased during exclusion conditions as the other players' facial resemblance to the participants increased. Although we predicted that the activation from the different conditions would fit a linear function (i.e. self-resemblance
other-race), we found increased activation in the ACC in both the same-race and self-resembling conditions. The activation in the ACC was less during the other-race exclusion condition. This indicates that individuals have a stronger neurological response to exclusion by members of self-referential and same-race in-group. This is not entirely surprising; as past research has suggested that cues of relatedness (self-resemblance and shared ethnicity) engender positive pro-social feelings (DeBruine et al., 2005
; Platek et al., 2009
; Rushton et al., 1984
). Individuals show a preference towards familiar stimuli; which, at the most basic level, would include individuals of the same-race.
We also found that individuals are not only affected neurologically, but participants also reported a decrease in satisfaction of four basic needs (belonging, control, self-esteem, and meaningful existence) when excluded. However, contrary to our prediction, participant's ACC activation showed a correlation to self-reported needs satisfaction in the same-race exclusion condition only. We hypothesized that there would be a correlation among the ACC activation and the self-resembling condition as well. Perhaps self-resembling and other-race faces represent the opposite ends of a self-referential distribution. For instance in the self-resemblance condition, one could be upset by exclusion from this class of stimuli, generally, without evaluation. On the other hand, exclusion by an other-race face is not upsetting because this class of stimuli may represent an out-group membership. However, in the same-race condition the players may represent persons who are members of the same social group, and whom might share genes in common with the participant. Perhaps in this instance, in the absence of ostensible cues to relatedness, the emotional feelings about the situation and the person modulate one's reactions to exclusion. That is, the lower individuals' rate their feelings of control and self-esteem, the more it hurts to be excluded by this person. It suggests that exclusion by individuals outside of our kin or other-race groups is modulated by feelings and needs associated with that person or group, but this idea demands more research.
Additionally, we found that activation in the ACC was correlated with activation in the RVPFC and LVPFC during the other-race exclusion condition. We did not predict this activation pattern. We hypothesized that activation in the VPFC would increase as activation in the ACC decreased, particularly during the self-resembling and same-race exclusion conditions. The VPFC is involved in the regulation and inhibition of the social pain response during exclusion(Eisenberger et al., 2003
). It is possible that we found a positive correlation between ACC activation and VPFC activation in the other-race condition because activation in the ACC was low to begin with in this condition. Alternatively, perhaps we found different activation patterns between the ACC and the areas of frontal cortex than the previous study (Eisenberger et al., 2003
) because we displayed faces to represent the other players. Thus, we may have unwittingly introduced another component that the frontal cortex was attending to in place of mediating ACC activation. Haxby et al. (2002
) describe the OFC (which we refer to as VPFC in this paper) as part of a neural system that participates in face perception and discuss its role in evaluating potential reward. This area seems to be instrumental in evaluating the information in faces that is relevant to social reinforcement, such as identity and expression (see Rolls, 1996
). It is plausible that VPFC activation was positively correlated with ACC activation in our study, particularly in the other-race condition, because the participants were paying specific attention to and assessing the faces for cues to emotional expression, as well as identity.
Finally, our results supported our hypothesis regarding the IAT and neural activation. Individuals who showed increased positive bias towards same-race images, showed a trend towards increased activation in the left and right amygdala during the other-race exclusion conditions. We also found a significant decrease in amygdala activation in the left amygdala in the same-race exclusion round. This suggests that as IAT score increased (implicit bias against other-race increased), participants showed a decrease in left amygdala activation when excluded by the same-race faces. This finding supports previous research regarding the importance of the amygdala in response to in- and out-group determinations and judgements (Phelps et al., 2000
). Phelps et al. (2000
) found that amygdala activation was correlated with both IAT reaction time as well as a startle eye-blink response when white participants were shown black faces. Thus, it appears that the amygdala is a primary component in the neural system involved in the response and appraisal of social groups possibly helping to make determinations regarding social group dynamics (see S.M. Platek and A. Krill, submitted).
Overall, the current results showed that individuals respond differentially to exclusion based upon level of resemblance to oneself and one's same-race group. These findings are significant in understanding how people respond to others in social situations based upon two important social cues: race and kinship. We were unable to test for gender effects. In our study there were only three males; therefore the majority of the participants were females. While we did not anticipate any significant sex effects, as the previous social exclusion literature has not revealed much in the way of sex effects, we cannot rule them out because we were unable to test for them given our sample.
Our results show that sharing race tends to make exclusion a more powerful and negative experience; whereas exclusion by an other-race has less of an impact. Unfortunately, we were not able to identify the mechanisms by which exclusion was more distressing in response to self-resembling and same-race faces. One possibility might involve differences in the feeling of development of a closer bond with the other players during the game. Future researchers could measure the development of a bond, feelings of trust, or positive or negative association feelings towards the other players during the Cyberball game. This would be a fertile area for future research and answer some of the questions left unanswered in our study. Furthermore, an examination of sex differences in social exclusion would also shed some light on an area that we were unable to investigate given our sample.