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Michael Spranger
The Evolution of Grounded Spatial Language


This thesis contributes to our understanding of the origins of spatial language by carrying out language game experiments with artificial agents instantiated as humanoid robots. It tests the theory of language evolution by linguistic selection, which states that language emerges through a cultural process based on the recruitment of various cognitive capacities in the service of language. Agents generate possible paradigmatic choices in their language systems and explore different language strategies. Which ones survive and dominate depends on linguistic selection criteria, such as expressive adequacy with respect to the ecological challenges and conditions in the environment, minimization of cognitive effort, and communicative success. To anchor this case study in empirical phenomena, the thesis reconstructs the syntax and semantics of German spatial language, in particular German locative phrases. Syntactic processing is organized using Fluid Construction Grammar (FCG), a computational formalism for representing linguistic knowledge. For the semantics the thesis focusses in particular on proximal, projective and absolute spatial categories as well as perspective, perspective reversal and frame of reference. The semantic investigations use the perspective of Embodied Cognitive Semantics. The spatial semantics is grounded in the sensorimotor experiences of the robot and made compositional by using the Incremental Recruitment Language (IRL) developed for this purpose. The complete reconstructed system allows humanoid robots to communicate successfully and efficiently using the German locative system and provides a performance base line. The reconstruction shows that the computational formalisms, i.e. FCG and IRL, are sufficient for tackling complex natural language phenomena. Moreover, the reconstruction efforts reveal the tight interaction of syntax and semantics in German locative phrases. The second part of the thesis concentrates on the evolution of spatial language. First the focus is on the formation and acquisition of spatial language by proposing strategies in the form of invention, adoption, and alignment operators. The thesis shows the adequacy of these strategies in acquisition experiments in which some agents act as learners and others as tutors. It shows next in language formation experiments that these strategies are sufficient to allow a population to self-organize a spatial language system from scratch. The thesis continues by studying the origins and competition of language strategies. Different conceptual strategies are considered and studied systematically, particularly in relation to the properties of the environment, for example, whether a global landmark is available. Different linguistic strategies are studied as well, for instance, the problem of choosing a particular reference object on the scene can be solved by the invention of markers, which allows many different reference objects, or by converging to a standard single reference object, such as a global landmark. The thesis demonstrates that the theory of language evolution by linguistic selection leads to operational experiments in which artificial agents self-organize semantically rich and syntactically complex language. Moreover, many issues in cognitive science, ranging from perception and conceptualization to language processing, had to be dealt with to instantiate this theory, so that this thesis contributes not only to the study of language evolution but to the investigation of the cognitive bases of spatial language as well.