A formal model of interpersonality

Capturing the complexity of interpersonal dynamics – emerging from the approach and avoidance motivation of two individuals in dyadic interplay that unfolds simultaneously on multiple time scales in order to satisfy their psychological needs – remains a scientific challenge. In line with calls for embracing complexity in psychological research using formal modeling, the purpose of this mathematical, non-data-driven (and thus not preregistered) study is to investigate the underlying mechanisms of the formation and maintenance of interpersonal relationships using evolutionary game theory. After formalizing interpersonal situations based on the affiliative motives of their interactants, a relational state space is constructed that reflects the ways of relating available to the interactants in the momentary state of their interpersonal relationship. This allows for modeling the evolution of an interpersonal relationship as a trajectory – driven by positive and negative reinforcement – in the relational space. Depending on the motives of both interactants, three qualitatively different interpersonal dynamics emerge: (1) global stability with only one relational attractor (e.g., an interpersonal relationship of pure friendliness in the long run), (2) bistability with two mutually exclusive relational attractors (e.g., either pure friendliness or pure distance), and (3) cyclicality with periodic orbits in the relational space (e.g., oscillation between friendliness and distance). Grounded in empirically supported psychological constructs, the formal model generates the well-known pattern of interpersonal complementarity. Over and above, novel interpersonal patterns emerged that might point to some underlying mechanisms of the interpersonal maintenance of psychopathology. The numerous model limitations as well as avenues for empirical tests and further development are discussed.