A crucial step for understanding how lexical knowledge is represented is to describe the relative similarity of lexical items, and how it influences language processing. Previous studies of the effects of form similarity on word production have reported conflicting results, notably within and across languages. The aim of the present study was to clarify this empirical issue to provide specific constraints for theoretical models of language production. We investigated the role of phonological neighborhood density in a large-scale picture naming experiment using finegrained statistical models. The results showed that increasing phonological neighborhood density has a detrimental effect on naming latencies, and re-analyses of independently obtained data sets provide supplementary evidence for this effect. Finally, we reviewed a large body of evidence concerning phonological neighborhood density effects in word production, and discussed the occurrence of facilitatory and inhibitory effects in accuracy measures. The overall pattern shows that phonological neighborhood generates two opposite forces, one facilitatory and one inhibitory. In cases where speech production is disrupted (e.g. certain aphasic symptoms), the facilitatory component may emerge, but inhibitory processes dominate in efficient naming by healthy speakers. These findings are difficult to accommodate in terms of monitoring processes, but can be explained within interactive activation accounts combining phonological facilitation and lexical competition.
2Reconciling phonological neighborhood effects in speech production through single trial analysis Native speakers of a language know a myriad of different words. This so-called mental lexicon is often described as an interconnected network in which representation distance may depend on meaning or form similarities among the words. One crucial step for understanding this network is to describe which kind of similarity influences language processing and how it modulates performance. In this context, the current research is concerned with the role of phonological similarity in word retrieval and speech production. This issue has been addressed in earlier theoretical work (e.g. Chen & Mirman, 2012;Dell & Gordon, 2003), but the empirical evidence on which this work is grounded remains controversial. Our goal in this article is to clarify the empirical facts regarding form similarity effects in speech production, and to integrate them within a single account. Clearing the empirical constraints will allow further refinement of theoretical models to advance our understanding of the cognitive processes underlying speech production.An approximation of how similar or interconnected a word is within the lexical network can be obtained by computing its phonological neighborhood density (PhND). PhND refers to the number of words that can be formed from a given word by substituting, adding or deleting one phoneme (Luce, 1986). For example, the word "bat" sounds similar to many other words (e.g., "cat", "fat",...