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 due to empirical evidence being consistent with both the cognitive and the historical approach. This article argues that phonology offers a unique test case for distinguishing historical and cognitive influences on grammar, and it proposes an experimental technique for testing the cognitive factor which controls for the historical factor. The article outlines a model called catalysis for explaining how learnability influences phonological typology and presents experiments that simulate this process. Central to this discussion are unnatural phonological processes, that is, those that operate against universal phonetic tendencies and require complex historical trajectories in order to arise. By 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 those of the cognitive approach, the experimental technique proposed in this article 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 a link between synchronic preferences and typology that is most likely not influenced by historical biases. Results suggest that complexity avoidance is the primary influence cognitive bias has 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.