We report two experiments that assessed the role of orthography in constraining subject-verb agreement in written (Experiment 1) and spoken (Experiment 2) French. We contrasted a condition in which the singular and plural forms of the subject head nouns were homophones but non-homographs (e.g., chanson, song-S, vs. chansons, songs-P) with a condition in which the subject head nouns were homophones and homographs in their singular and plural forms (e.g., refus, refusal-S,P). An effect of the orthographic marking was found in written production but not in oral production. The results, together with our previous findings, suggest modality-specific feedback effects during grammatical encoding: orthographic representations influence written production but morpho-phonological representations influence oral production.
Franck, J., Bowers, J., Frauenfelder, U., & Vigliocco, G. (2003). Orthographic influences on agreement: A case for modality-specific form effects on grammatical encoding. Language and Cognitive Processes, 18(1), 61-79. https://doi.org/10.1080/01690960143000452 (Original work published 2003)