Non-arbitrariness in novel sign systems
Theisen, Carrie Ann
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This thesis investigates non-arbitrariness in novel sets of signs (mappings between signals and meanings). Two common ways of characterizing signs – by the degree of motivatedness they exhibit and by the degree of systematic compositionality they exhibit – are not necessarily orthogonal. Thus, the emergence of arbitrariness and of systematic compositionality in language should be studied together. We focus on a particular interface of the two properties: the systematic re-use of arbitrary elements. Previous work that demonstrates how novel signs can emerge and then evolve to become arbitrary does not measure systematic compositionality. On the other hand, previous work on systematic compositionality proposes a mechanism for the evolution of systematic compositionality and a measure of the property, but does not address the evolution of arbitrariness. We propose a parallel theory of the emergence of the systematic re-use of arbitrary elements. Systematic compositionality emerges in novel, motivated signs and is maintained as the signs become arbitrary. We report a series of experiments that probe how the systematic re-use of arbitrary elements arises in novel communication systems. In Experiment 1, partners must create signs from scratch to communicate about items that share semantic features. The systematic re-use of arbitrary elements emerges. Further, the evolution of arbitrariness and systematic compositionality are parallel: even participants’ first drawings of items are systematically compositional, and this systematic compositionality is maintained as the signs become arbitrary. Experiment 2 demonstrates that naïve participants, who played no role in – indeed, did not even observe – the creation of the sign systems, can nonetheless detect the systematic compositionality in them and generalize from it. Experiment 3 shows that participants actually do make use of the systematic re-use of arbitrary elements that they observe in others’ sign systems, when faced with the task of communicating (rather than learning and reproducing). The systematic compositionality is not only maintained, but appears to be increasing, over generations of participants observing others’ signs. The increase in systematic compositionality occurs when pairs create signs for items they have not observed – presumably, as they generalize using the systematic compositionality they have observed. In sum, we present an alternative mechanism for the emergence of the systematic reuse of arbitrary elements: arbitrariness and systematic compositionality emerge in a parallel fashion within the dyad, and subsequent communicators maintain – or even increase – the structure they have observed. More generally, we demonstrate the importance of examining arbitrariness and systematic compositionality together.