What governs a language's lexicon? Determining the organizing principles of phonological neighbourhood networks

The lexicons of natural language can be characterized as a network of words, where each word is linked to phonologically similar words. These networks are called phonological neighbourhood networks (PNNs). In this paper, we investigate the extent to which observed properties of these networks are mathematical consequences of the definition of PNNs, consequences of linguistic restrictions on what possible words can sound like (phonotactics), or consequences of deeper cognitive constraints that govern lexical development. To test this question, we generate random lexicons, with a variety of methods, and derive PNNs from these lexicons. These PNNs are then compared to a real network. We conclude that most observed characteristics of PNNs are either intrinsic to the definition of PNNs, or are phonotactic effects. However, there are some properties—such as extreme assortativity by degree—which may reflect true cognitive organizing principles.