The Imagined We: Shared Bayesian Theory of Mind for Modeling Communication
How can a pointing gesture or simple utterance come to mean so much? Unlike a code or fixed mapping that can be used to uniquely identify a referent, humans flexibly use the same signal to mean many different things. As a result, to formally capture the impromptu, sparse nature of communication, it should be viewed as an inferential process. Both sending and understanding a signal in context requires reasoning about the underlying mind at the other end. This dissertation takes a cognitive approach to developing a computational framework for this type of uniquely human communication. Even young children who cannot yet speak in full sentences use simple gestures and utterances in uniquely flexible and intelligent ways. This highlights the promise of a reverse engineering approach: the underlying cognitive mechanisms and commonsense reasoning accumulated during pre-linguistic development become the foundation for modeling intelligent communication.
The modeling approach taken here formalizes this theoretical account by connecting and extending three lines of work which have traditionally been viewed as separate domains. First, I adopt an existing model that draws from game theory and probabilistic inference to formalize flexible signal understanding. Second, I integrate this with socially rational models of individual agency, which involve understanding why individuals act the way they do in terms of their underlying mental states. This follows the tradition of viewing communication as an inference problem, where understanding a signal is about understanding the underlying mind that generated it. Here I argue communication can be viewed in terms of its use: signals are a special type of rational action that can be used to coordinate individuals. This perspective connects modeling flexible signaling to models of intentional agents. Finally, my last step is to shift from individual agency to treating communication as a cooperative, shared agency problem. While shared agency has been a promising approach for coordinating cooperators, it has not yet been modeled in conjunction with communication. This dissertation bridges this gap, leading to the development of a novel framework for communication, called the Imagined We (IW). I justify this cooperative shared agency approach by drawing from a wealth of behavioral evidence in developmental and comparative psychology demonstrating how communication can be viewed as a way to facilitate increasingly sophisticated cooperation. Through a set of simulations in cooperative tasks, I demonstrate theoretical advantages of this perspective. Moreover, I combine this with behavioral evidence that can begin to support some of the theoretical claims this model makes.