We examine five spontaneous dialogues conducted in Japanese and analyze the potential of speech rate change to signal the structure of information being exchanged in dialogue. We found (1) a bi-directional correlation between speech decelerations and the openings of new information, and (2) another bi-directional correlation between speech accelerations and the absence of information openings. Our data show that the correlations hold not only in the case of a single speaker's speech, but also in the case of multiple speakers' sequential utterances, with or without turn shifts. We also study possible disturbances to these default correlations and identify the limitation on speakers' cognitive resources as one major constraint that interferes with the accurate signaling of information opening by decelerated speech.

Edioic responses abound in dialogues, where a speaker reuses a portion of the text uttered by another in a preceding turm, though semantically they contribute little if any new information. The phenomenon has attracted the attention of researchers from diverse academic fields, ranging from sociolinguistics and developmental psychology, to computational linguistics and human-computer interfaces. This study reports an empirical investigation on echoic responses from an informational perspective. Drawing on statistical analyses of instances extracted from corpora of spoken dialogues in Japanese, we show that echoic responses with different timings, lengths, intonations, pitches, and speeds signal different degrees in which the speakers have integrated the repeated information into their prior knowledge. We further consider dialogue-coordination functions enacted by this informational potential of echoic responses, and identify the function of display as distinguished from the functions of acknowledgment and repair-initiation.