PROJECT SUMMARY/ABSTRACT Children who exhibit externalizing problems including conduct problems, oppositional defiance, and attention- deficit hyperactivity symptoms exhibit significant psychological difficulties and incur substantial societal and economic costs. One identified early risk factor for children’s externalizing difficulties is callous-unemotional (CU) traits, defined by indifference and apathy and diminished sense of guilt and empathy for others. Prior work has been limited to investigations of correlates of CU traits and externalizing behaviors separately. However, research has yet to examine process-oriented models to identify explanatory risk mechanisms of the relation between children’s CU traits and later externalizing problems. Understanding the underlying processes of this association may help to further refine current early childhood interventions and identify important targets necessary to disrupt the pathogenic cascade and ensuing externalizing difficulties. Therefore, the present study plans to address this gap by examining three distinct classes of risk mechanisms as mediators of the relation between children’s CU traits and subsequent externalizing problems. First, although conceptual models propose that CU traits modify how children’s encoding and processing of emotional cues and consequently their increased aggressive behavior towards others, no studies have examined children’s emotion-biased attentional processes as a risk mechanism of CU traits and externalizing problems. Thus, the current study examines children’s attentional biases to happy, angry, and sad faces as mediators of this association (Aim 1). Second, research has indicated that children with CU traits may also experience deficits in emotion understanding, including emotion identification and emotion perspective taking. In turn, children with high CU traits are posited to have difficulties tailoring their responses to others due to deficits in understanding the meaning and consequences of emotional displays. Thus, this project proposes to test children’s emotion understanding as an explanatory risk mechanism in the relation between children’s CU traits and later externalizing problems (Aim 2). Lastly, given children with CU traits are more likely to have deficits in the motivation to recruit resources to address challenges in the environment, this may be instantiated in dampened reactivity across both the parasympathetic (PNS) and sympathetic (SNS) nervous systems. Thus, the proposed research will examine whether children’s physiological reactivity mediates the prospective association between CU traits and externalizing problems (Aim 3). This work addresses the limitations of prior research by leveraging existing data from a multimethod (i.e., surveys, observations, physiology, eye-tracking), multi-informant (i.e., mother, partner, child), multilevel (i.e., behavioral, cognitive, biological), longitudinal study of 238 families and their preschool children...