The Processing of Sentence-Level Speech Prosody

Prosody plays an important role in spoken language perception. It assists not only in segmenting the individual words in the often continuous speech signal, but also in segmenting greater chunks of speech consisting of several words, such as phrases and sentences. We have explored two ways by which to investigate the processing of phrase- or sentence-level prosody, that is, first, by studying the processing of phrase boundaries and, second, by comparing normal speech with hummed sentences. Phrase boundaries are a global prosodic characteristic. Within sentences in German, for example, they are often prosodically realized by a rising pitch, a lengthening of the vowel preceding the boundary and a pause before the onset of the next phrase. When a spoken sentence is hummed, all segmental information is lost and only its intonation is preserved. In previous EEG experiments conducted by our group a phrase boundary in an auditorily presented sentence has been observed to cause a positive shift in the event-related averaged signal, which is referred to as the closure-positive shift (CPS). This EEG component seems to be very robust and has also been observed at phrase boundaries in hummed versions of sentences. We will report the results of an fMRI experiment that investigated the neural correlates of the CPS component as observed in EEG at phrase boundaries and that compared the processing of normal speech with the processing of hummed sentences. In this experiment, it has been observed that an additional phrase boundary leads to a greater activation of areas in the right superior temporal gyrus adjacent to the primary and secondary auditory cortices. Normal speech activated areas in the temporal lobe bilaterally as well as areas in the supramarginal gyrus, the inferior frontal gyrus, the thalamus and the cerebellum more strongly than hummed sentences.