Catching the news: Processing strategies in listening to dialogs as measured by ERPs

BACKGROUND: The online segmentation of spoken single sentences has repeatedly been associated with a particular event-related brain potential. The brain response could be attributed to the perception of major prosodic boundaries, and was termed Closure Positive Shift (CPS). However, verbal exchange between humans is mostly realized in the form of cooperative dialogs instead of loose strings of single sentences. The present study investigated whether listeners use prosodic cues for structuring larger contextually embedded utterances (i.e. dialogs) like in single sentence processing. METHODS: ERPs were recorded from listeners (n = 22) when presented with question-answer dialogs in German. The prosody of the answer (target sentence) either matched the context provided by a question or did not match the context question. RESULTS: CPS responses to the processing of the target sentences are elicited, first, when listeners encounter information comprising 'novelties', i.e. information not mentioned in the preceding question but facts corrected between context and target. Thereby it is irrelevant whether the actual prosody of the target sentence is in congruence with the informative status or not. Second, when listeners encounter target sentences which do not convey any novelties but only previously 'given' already known information, the structuring of the speech input is driven by prosody again. The CPS is then elicited when listeners perceive major prosodic boundaries similar as for the processing of context-free single sentences. CONCLUSION: The study establishes a link between the on-line structuring of context-free (single sentences) and context-embedded utterances (dialogs) as measured by ERPs. Moreover, the impact of prosodic phrasing and accentuation on the perception of spoken utterances on and beyond sentence level is discussed.