In psychodrama, doubling is a technique where a participant, perhaps asked by the psychodrama director, supplements the role (self, role reversal) of the protagonist, usually by standing behind them and saying things that the protagonist might want to say or is withholding. The person performing the supplemental role is commonly called the Double. The task of the Double is to provide a link between the patient's internal reality and the external environment. In this way one is able to hear things that may (or not) reflect what they feel or think. Thereby, the doubling can help provoke abreactive and mental catharsis, insight, and transformation.
^Hudgins, M. K., & Kiesler, D. J. (1987). Individual experiential psychotheraphy: An analogue validation of the intervention module of psychodramatic doubling. Psychotherapy: Theory, Research, Practice, Training, 24(2), 245-255.