Segmental and metrical encoding in aphasia: Two case reports

Abstract

Background: Phonological impairment in aphasic patients most often affects the segmental structure of words, while metrical structure, i.e., syllable number and stress position, is usually preserved. There is an ongoing discussion on the question of where segmental and metrical errors may occur during the process of word form encoding. In the context of this discussion, a theoretically important aspect is how aphasic phonological impairment interacts with syllabification. Aims: Two aphasic patients with phonological output impairments are described to demonstrate that (1) disturbances of metrical and segmental structure can be dissociated and (2) aphasic phonological impairment may or may not interfere with syllabification. Methods and Procedures: Single case study of word repetition. Outcomes and Results: Patient WK had an impairment of metrical encoding with largely preserved segmental encoding processes. More specifically, he had a strong tendency to produce the unmarked metrical pattern of German, i.e., two-syllabic words stressed on the first syllable (trochaic pattern). JS showed a reverse pattern with preserved metrical structure but severely affected segmental encoding. While the pathomechanism underlying WK's impairment operated on unsyllabified representations, JS's error pattern was sensitive to syllable structure. Conclusions: (1) At a lexical stage, metrical and segmental retrieval are two parallel processes which can be impaired independently. (2) Postlexically, these two types of information are combined in the syllabification process. The two cases show that phonological errors may arise before syllabification (i.e., at the lexical stage of word-form encoding) or at a stage after phonological words have been syllabified.