Distinguishing cognitive from historical influences in phonology

Distinguishing cognitive influences from historical influences on human behavior has long been a disputed topic in behavioral sciences, including linguistics. The discussion is often complicated by empirical evidence being consistent with both the cognitive and the historical approach. This paper argues that phonology offers a unique test case for distinguishing historical and cognitive influences on grammar and proposes an experimental technique for testing the cognitive factor that controls for the historical factor. The paper outlines a model called catalysis for explaining how learnability influences phonological typology and designs experiments that simulate this process. Central to this discussion are unnatural phonological processes, i.e.~those that operate against universal phonetic tendencies and that require complex historical trajectories to arise. Using statistical methods for estimating historical influences, mismatches in predictions between the cognitive and historical approaches to typology can be identified. By conducting artificial grammar learning experiments on processes for which the historical approach makes predictions that differ from the cognitive approach, the experimental technique proposed in this paper controls for historical influences while testing cognitive factors. Results of online and fieldwork experiments on two languages, English and Slovenian, show that subjects prefer postnasal devoicing over postnasal fricative occlusion and devoicing in at least a subset of places of articulation which aligns with the observed typology. The advantage of the proposed approach over existing experimental work is that it experimentally confirms the link between synchronic preferences and typology that is most likely not influenced by historical biases. Results suggest that complexity avoidance is the primary influence of the cognitive bias on phonological systems in human languages. Applying this technique to further alternations should yield new information about those cognitive properties of phonological grammar that are not conflated with historical influences.