Are there independent lexical and nonlexical routes in word processing? An evaluation of the dual-route theory of reading

TLDR

Dual‑route theory proposes two independent processing routes—lexical access and nonlexical grapheme‑to‑phoneme conversion—and highlights three key topics: nonword processing, spelling‑regularity effects, and reading impairment after selective damage to either route. The study evaluates evidence on nonword processing, spelling‑regularity effects, and selective‑damage reading impairment, challenging the theory’s claim of an independent nonlexical route. The authors discuss alternative visual‑word‑processing models that assume lexical knowledge guides phonological assembly. The authors conclude that linguistic constraints limit nonlexical grapheme‑to‑phoneme conversion, and argue that the discussed alternative models should guide future research.

Abstract

Abstract One of the most popular and influential theories of word processing, dual-route theory, proposes that there are two functionally independent means of processing words, one involving access to lexical knowledge and the other involving nonlexical grapheme-to-phoneme conversion. Three topics germane to this theory are the processing of nonwords, spelling regularity effects, and the manner in which reading may be impaired following selective damage to either route. This paper evaluates evidence on these topics, and in each case the claims of the theory for an independent nonlexical processing route are called into question. This conclusion is further supported by a discussion of the linguistic constraints that limit any nonlexical grapheme—phoneme conversion process. Some alternative approaches to visual word processing, which share the assumption that lexical knowledge can guide the assembly of phonological information, are discussed. It is argued that these approaches should direct future research.