(noun) Emotional contagion is the arousal of emotions in one person after observing the emotions of another.

In their excellent research paper, Empathy: It’s ultimate and proximate bases, Stephanie D. Preston and Frans B.M. de Waal explain that the difference between empathy and emotional contagion is in the lack of “self-other distinction”. In other words, the difference is that in emotional contagion, the persons involved lacked boundaries.

Preston and de Waal continue, explaining that there is not always a clear distinction between empathy and emotional contagion:

The distinction between empathy and emotional contagion is empirically based and provides good guidelines for categorizing behavior. Individuals who are overly distressed tend not to help while individuals that are emotionally involved and concerned tend to help (Batson et al. 1987; Doherty 1997; Eisenberg et al. 1994; 1998; Eisenberg & Okun 1996; Rice 1964). However, these heuristics should not cause one to overemphasize the distinction between emotional contagion and empathy. The two share their underlying process and cannot be totally disentangled (as also suggested by Thompson 1987). For example, it is a mistake to assume that one cannot simultaneously be highly distressed and maintain the self/other distinction. Similarly, it is a mistake to assume that one who offers help through empathy is not also acting to diminish negative affect. By design, empathy involves some level of emotional contagion and personal distress (at least at the representational level), and helping is never entirely for the sake of the object.

The paper is comprehensive on the subject of empathy and it describes psychopathy as a condition of little or no empathy.  What it doesn’t address is emotional contagion from psychopaths.

I’ve witnessed psychopaths play out melodramatic scenes with the intent to arouse emotions in their victims, emotions which they themselves, don’t feel at all.  Conversely, we have all experienced the slime which a psychopath transfers to his victims without ever showing any sense of shame at all.