Cognitive theories have proposed that major depressive disorder (MDD) and social anxiety disorder (SAD) involve attentional biases toward and away from specific environmental stimuli. Research has often examined these biases in response to emotional facial expressions, but evidence of attentional biases is mixed. An event-related potential called the N2pc offers advantages over other measures of attentional bias and may clarify conflicting findings. Studies on the N2pc and social anxiety have found consistent results, but there is little work examining depression. Previous N2pc studies are limited by the types of emotional faces they use and by comparing attention for emotional faces only with neutral faces. Further, the effect of MDD-SAD comorbidity has not been thoroughly examined using the N2pc. In this study, undergraduate participants completed self-report questionnaires of depression and social anxiety symptoms. Electroencephalography and reaction time (RT) data were collected during a modified dot-probe task that put emotional faces (angry, disgust, sad, and happy) in direct competition with each other and with neutral faces. ANCOVAs predicting the N2pc and RT showed that no depression or social anxiety-related attentional biases were stronger for any one face type relative to biases for the other face types. However, multiple regressions predicting attentional bias toward specific face type showed that depression and social anxiety interacted to predict attentional biases. Depression was associated with an N2pc attentional bias toward sad faces when social anxiety was low. Social anxiety was related to an N2pc attentional bias away from angry faces at low depression and towards angry faces at high depression, and there was an RT attentional bias away from disgust faces at low depression. Additionally, depression was related to an attentional bias away from neutral faces, while social anxiety was related to a bias toward them. These findings bolster evidence of a sad-related bias in depression and social threat-related biases in social anxiety but highlight the generally overlooked impact of co-occurring symptoms. Interventions for MDD and SAD should target attentional biases in a nuanced manner that considers comorbidity and patterns of both vigilance for and avoidance of social stimuli
