1. Introduction
The dynamics of social interactions between two people can be decomposed into a sequence of action and reaction pairs (such as pointing and sharing a point of attention, gesturing and nodding in agreement, or laughing and gesturing disagreement) to convey to each other a sense of their internal states. Our everyday interactions even include micro-actions and micro-reactions in which only subtle body motion is apparent, such as slight changes in focus of attention (small movement of the head in response to pointing), subtle nodding, or small hand actions. The ability to understand interaction dynamics with such micro-behaviors is important for human-to-human communications, as this mode of non-verbal communication is perhaps our primary means of understanding and expressing our internal state. Towards understanding the deeper complexities of social interaction dynamics, this work attempts to take the first step by developing a method to recognize micro-actions and reactions.
Challenges of recognizing micro-actions. Slight head motion of person induces only slight local motion in the person 's points-of-view in (1) and (2). Hand motion by person is difficult to observe from the 's points-of-view in (2) and (3).