Eliminating unpredictable linguistic variation through interaction

Languages tend not to exhibit unpredictable variation. We explore alignment/accommodation during interaction as a mechanism to explain this cross-linguistic tendency. Specifically, we test the hypothesis (derived from historical linguistics) that interactions between categorical and variable users are inherently asymmetric: while variable users (of e.g. a grammatical marker) can accommodate to their partner by increasing their usage, categorical users should be reluctant to accommodate to variable partners, since this requires them to violate the rules of their grammar. We ran an experiment in which pairs of participants learnt a miniature language (featuring a potentially variable grammatical marker) and then used it to communicate. Our results support the hypothesis: variably-trained participants accommodate to their categorically-trained partners, who do not change their behaviour during interaction. More generally, interaction results in the elimination of variation: accommodation/alignment is a viable mechanism for explaining the absence of unpredictable variation in language.