Sonority substitutions in Broca's and conduction aphasia

Conduction aphasia is characterized by the production of phonemic paraphasias. These errors are assumed to be attributed to a breakdown in phonological processing, that is, in transforming the underspecified lexical-phonological form into a phonemic representation. Some Broca's aphasics also produce a considerable number of phonemic errors, due to a disorder in phonetic processing, namely, planning and executing the articulatory programs. Despite the fact that the phonemic errors in these two aphasia types arise at different levels, they are hard to distinguish. Some phonologists suggested that a distinction should be made between articulatorily based and phonologically based features. Although most features can be accounted for in articulatory terms (e.g. voice, labial), some are primarily motivated for phonological tasks. One of those features is [sonorant]. It is therefore hypothesized that substitutional errors concerning sonority will occur in conduction aphasia, but not in Broca's aphasia. This hypothesis has been tested and the results show that conduction aphasics indeed produce significantly more sonority substitutions than Broca's aphasics, but that the latter group does produce a few sonority substitutions as well. Several explanations for these phenomena are discussed.