Bidirectional grammar and bidirectional optimization
The human language faculty is a bidirectional system, i.e. it can be used by processes of approximately equal computational complexity to understand and to generate utterances of a language. We assume the general framework of optimality theory and treat the language faculty as a constraint-based system where the very same constraints are uses both in comprehension and in generation. In the simplest case comprehension and generation can be modelled by unidirectional optimization: finding an optimal interpretations for a given speech input in the case of comprehension; producing an optimal expression for a given message in case of generation. In the simplest case, the speaker and the listener roles are strictly separated. However, there are linguistic observations which indicate that the listener’s and the speaker’s perspectives are integrated to some extent. Bidirectional optimization is an explicit proposal for doing the integration. In this article we propose a general architecture of the language faculty and discuss the precise extent to which speakers are listener-oriented and/or listeners are speaker-oriented. Interestingly, this extent does not seem to vary with regard to the different subsystems considered: the sensorimotor system, the system of grammar proper and the conceptual-intentional system (pragmatics). Though the experimental evidence is not very strong at the moment it seems in online processing the speaker takes the hearer into account but not <i>vice versa</i>. Besides the online (actual processing) view of bidirectionality we discuss bidirectional optimization as an offline phenomenon taking place during language acquisition, and giving raise to fossilization phenomena.