Stem Homograph Inhibition and Stem Allomorphy: Representing and Processing Inflected Forms in a Multilevel Lexical System Mark Allen and William Badecker Johns Hopkins University Two lexical decision experiments were carried out in Spanish in order to address questions about the processing and representation of morphologically complex words in the mental lexicon. Re- sponses to targets (e.g., mor-os “Moors”) were found to be reliably slower and less accurate when they were preceded by stem homograph primes (mor-ir “to die”) compared to unrelated control primes (sill-a “chair”), and this inhibitory effect was over and above the marginal reaction time effect for morphologically unrelated primes that shared just as much left-to-right orthographic overlap with the target stem as the stem homograph primes (moral “moral”). We take this as evidence that the stem homograph effect is a direct consequence of morphological decomposition in lexical access. In a second experiment, an inhibitory effect was observed when the same targets were preceded by primes that were not themselves stem homographic with the target, but rather allomorphically related to stems that were stem homographs (muer-e “she/he/it dies”). Since target inhibition was found for primes whose inflectional stems are not strictly ambiguous at the level of form, this pattern of results provides evidence for morphologically abstract (lemma-like) representations that are engaged in lexical access at a form-neutral level of morpholexical processing. © 1999 Academic Press Key Words: Language; morphology; inflection; stem homographs; allomorphy. Language processing requires recognition and production mechanisms that can accommo- date two extremes of familiarity. At the sen- tence level, combinations of forms (i.e., words and phrases) may occur in sequences that have never been observed. This means that the pro- cessing system must include representations and procedures for interpretation which exploit combinatory mechanisms. For the production/ comprehension of simple (i.e., monomorphe- mic) words, though, the arbitrary character of the sequence of the sublexical units that make up a word entails that the processing system must also include a means for dealing with vast stores of memorized linguistic structures. Lex- ical morphology, however, plays an intermedi- ate role between the processing extremes of full combinatorial productivity and rote memoriza- tion. On the one hand, we often encounter mor- phologically complex words comprised of novel combinations of morphemes (much in the same way that we encounter novel combina- tions of words or phrases in sentence process- ing). Nevertheless, we are able to calculate the meanings of these novel constructions by in- voking our knowledge of the individual mean- ings of the word’s morphemes and our knowl- edge of the (rule-like) combinatorial properties of these morphemes. Therefore, decomposi- tional mechanisms in lexical recognition are necessitated by the fact that productive mor- phemes (e.g., -est, -ly, -ed, -ing) can be parsed and recognized independently of the other mor- phemes with which they happen to occur. On the other hand, many morphologically complex words that we encounter are words that we have used and recognized many times before. In these cases, it appears as though a processing system that stores and retrieves whole-word representations would be capable of executing We are grateful to Dr. Jose Manuel Igoa for his willing assistance in preparing stimuli, recruiting participants, and providing the facilities necessary to carry out this research. Thanks to Luigi Burzio, Kath Straub, Brenda Rapp, Colin Wilson, Fero Kuminiak, Matt Goldrick, and three anony- mous reviewers for helpful comments on earlier drafts of this paper and to Danielle Vignati for preparing statistical analyses of the experimental stimuli. Address correspondence to William Badecker, Depart- ment of Cognitive Science, Johns Hopkins University, Bal- timore, MD 21218-2685. E-mail: badecker@jhu.edu. 105 0749-596X/99 $30.00 Copyright © 1999 by Academic Press All rights of reproduction in any form reserved. Journal of Memory and Language 41, 105–123 (1999) Article ID jmla.1999.2639, available online at http://www.idealibrary.com on