Going on with optimised feet: Evidence for the interaction between segmental and metrical structure in phonological encoding from a case of primary progressive aphasia
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Background: Our knowledge about the interaction between segmental and metrical levels of representation in word production is still largely underspecified. In particular, there is only sparse evidence of how syllables are hierarchically organised into higher-level prosodic structures such as prosodic feet and words. Furthermore, the question whether stress assignment in German is sensitive to syllable weight is unresolved so far. While quantity-insensitive accounts state that stress is predominantly assigned to a default position (i.e., to the penultimate syllable) and other stress patterns are exceptional, quantity-sensitive accounts assume that stress assignment is determined by the weight of the final two syllables. Aims: Impaired lexical retrieval may lead to regularisations of stress assignment. Such an error pattern will be examined to gain insights into the interrelation between different tiers of prosodic representations (e.g., syllable, foot, prosodic word). Methods & Procedures: A reading and a repetition task were conducted with German-speaking patient HT, suffering from primary progressive aphasia, which especially affected her retrieval of lexical information. The material consisted of polysyllabic words with varying stress patterns and syllable structures. Outcomes & Results: In reading, HT produced hardly any segmental errors, but a substantial amount of stress errors. Importantly, the patient not only over-generalised the default penultimate stress as would have been predicted by quantity-insensitive approaches. Instead, she over-applied different stress patterns depending on the weight of the last two syllables. In repetition, HT's output can be characterised as phonological jargon. Crucially, however, she hardly produced any stress errors. Rather, thorough analyses revealed that segmental deviations in her output led to optimised prosodic structures. For instance, insertions of rhyme segments could be observed mainly in strong syllables, i.e., syllables bearing main or secondary stress, whereas deletions occurred predominantly in weak, unstressed syllables. Conclusions: The present data provide evidence for specific forms of interaction between segmental and metrical knowledge: On the one hand, segmental information influenced the patient's stress assignment errors in reading. On the other hand, prosodic information modified segmental errors even in severe jargon observed in repetition. With respect to the prosodic system of German, the observed error patterns show that the structure of the final syllable determines how syllables of a word are parsed into prosodic feet and, accordingly, which syllable has to be prominent. Thus, our results support quantity-sensitive approaches of stress assignment.