My research investigates dynamical systems models of human behaviour, evaluating these approaches for HCI research. I focus on how so-called interaction dominant (ID) dynamics in individual behaviour can be used to develop low cost an unobtrusive measures of skill learning, task-engagement, and executive function during interaction. ID dynamics are ubiquitous in human behaviour and indicate the central role of complex, nonlinear network effects. Changes in these ID dynamics have been related to high-level features of human behaviour and experience, many of which are of interest to HCI. I adapt this prior research to the conditions and concerns of HCI.