How modality-specific is morphology?

Writing has long been considered to be dependent on speaking. However, modality-specific dissociations between written and spoken word production imply that word production is supported by distinct neural mechanisms in writing, which can be impaired or spared regardless of the intactness of spoken word production. Rapp et al. (2015). Modality and morphology: What we write may not be what we say. Psychological Science, 26, 892-902 documented a double dissociation where problems with regular inflections were selectively restricted to writing or speaking. We report on two English-speaking aphasic individuals who exhibit this same modality-specific dissociation of inflectional processing, replicating the original findings. We expand on Rapp et al.'s study by examining whether the dissociations observed with regular inflections extend to other morphological forms, such as derivation and irregular inflection. Results showed that the dissociation holds for derivation; however, both participants were impaired with irregular inflections in both output modalities. Implications of these findings for morphological processing and the independence of the orthographic system are discussed.