The role of pragmatic mechanisms in referential communication and categorization: An emergent communication model.

We model pragmatic mechanisms of referential communication and categorization in a multi-agent framework of emergent communication. Pragmatic theories and experimental work predict that speakers consider the context in their choice of referring expressions. In addition to this context-based reasoning, utility-based pragmatic reasoning about the listener's likely interpretation of an utterance influences the speaker's production choices. We aim to investigate these two factors and their role in referring expression generation and categorization in a computational model of language emergence and language use. We model communication in interaction and consider an efficiency tradeoff between speaker and listener utilities. Our results show that an emerging language becomes more effective, ambiguous, and efficient when speakers and listeners communicate in a shared context. This is achieved by an efficient tradeoff between production and comprehension where languages can afford to be simpler in production when they are sufficiently informative in context, placing more burden on the listener's side. We further demonstrate that incorporating utility-based pragmatics, as modeled with the Rational Speech Acts framework, improves the linguistic efficiency of language use only in languages that emerged with a shared context between interlocutors, but not in languages that emerged without such contextual information during training. We conclude that context-based pragmatics plays a role in referential communication and categorization by shaping an emerging language. Efficient reference in a communicative situation can benefit especially from utility-based pragmatics if the language that is being used has emerged in context. This might suggest that utility-based pragmatics hinges on mechanisms that naturally emerge when context is available during the evolution of a language. In summary, we show that human-like language and category systems emerge as an optimized tradeoff between speaker and listener needs in interaction, i.e., under efficiency considerations of simplicity and informativeness.