Tier-adjacency is not a necessary condition for learning phonotactic dependencies

One hypothesis raised by Newport and Aslin to explain how speakers learn dependencies between nonadjacent phonemes is that speakers track bigram probabilities between two segments that are adjacent to each other within a tier of their own. The hypothesis predicts that a dependency between segments separated from each other at the tier level cannot be learned. Were this true, it could add psycholinguistic plausibility to phonological theories that limit possible nonadjacent dependencies to those between two tier-adjacent segments. Contrary to the prediction, the experiments in this paper show that adults can learn dependencies between two consonants that are nonadjacent to each other at the tier level as well as the segmental level. The results suggest that the range of learnable sound patterns may be wider than the range of attested sound patterns and that additional learning mechanisms should be considered to explain how speakers learn nonadjacent phonotactic dependencies.