The cognitive and interactional causes of regularity in language

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Why are humans special? Are we special because of our biology, or our capacity to learn from one another, or both? We address this fundamental question by studying the relationship between language universals, language learning, and language transmission. The languages of the world are superficially rather different: they employ different sounds and build complex utterances in different ways. However, all languages seem to share a common set of structural properties or design features. Where do these language universals come from? One influential hypothesis has suggested that they are a direct reflection of a highly-constraining blueprint for language, which children impose on language during language learning. An alternative possibility is that these properties might be due to weaker biases in learners, which have a very small impact for a particular child learning a particular language, but have a strong effect as a result of the transmission of language over thousands of such episodes of language learning. Linguistic variation has become a test-case for such questions. Languages exhibit variation: for instance, in English the precise way in which we pronounce the plural marker -s varies (e.g. sometimes "s", as in the plural "cats", sometimes "z", as in "dogs"). However, while it seems logically possible that this kind of variation could occur completely at random (e.g. speakers could randomly chose to use either "s" or "z" - so-called free variation), this type of behaviour very rarely (possibly never) occurs in human languages. Instead, linguistic variation is predictable (in the case of -s, the pronunciation is predictable from the last sound in the noun) i.e. predictable variation is a design feature of language. But why does language work like this? Some experiments seem to support the hypothesis that the lack of free variation in language is due to strong biases which children impose on language: children don't expect unpredictable variation, and therefore ignore or eliminate it during learning. These experiments use a methodology known as artificial language learning in which children and adults learn miniature languages (created by the experimenter) and are then tested to see whether they change aspects of the language when they use it themselves. Our own work using this same methodology suggests that the differences between children and adult learners may not be as clear cut as earlier work suggested. One of the objectives of the current project is to conduct further learning experiments in order to better understand this difference between adults and child learners, and the extent to which a single learner of any age can re-shape an input language. This first strand of research therefore studies how *individual* learners respond to unpredictable languages. However, as discussed above, the predictability of natural languages could be a consequence of very weak preferences in individual language learning and use, which accumulate over multiple generations. We will therefore run a second strand of experiments, using only adult participants, where people learn an unpredictable language, use it to communicate with a partner, and then transmit their language to other learners in a diffusion chain (an experimental equivalent to the parlour game "Chinese whispers", where language passes from person to person and potentially changes as it goes). These experiments, together with accompanying computational modelling, will allow us to simulate, in a very simple way, the transmission and use of language in a population. By combining both strands, we can begin to address the fundamental questions we outlined above: are the universal features of language necessarily due to strong restrictions on language design imposed by child learners, or can far weaker biases inherent in the processes of learning, transmission and use have strong effects on the structure of human language?