Abstract
We examine a classic problem in Spanish morphophonology as a way of shedding new light on the relationship between grammar and processing. Spanish derivations with diphthongizing stems may contain either the diphthong or the monophthong stem allomorph, but the likelihood of the (phonotactically marked) diphthong appearing is related to the productivity of the suffix. Prior data also indicate that this bias constrains the formal properties of possible, but as yet unattested derivations. Interestingly, the documented relevance of suffix productivity and stem phonotactics for lexical processing suggests a relationship between the processing characteristics of neologisms and their favored formal properties. Spanish diphthongization provides an ideal window on this relationship because the availability of either allomorph for any neologism allows us to compare the processing characteristics of the grammatically preferred and the dispreferred form. We present visual lexical decision results that confirm the systematic biases concerning Spanish diphthongization and shed light on their possible roots in processing. The results illuminate this long-standing conundrum in Spanish and point to a more general picture in which the impact of distributional properties of morphemes on processing can account for the current shape and dynamic evolution of the lexicon.