In this paper, I claim that utterance-final elements in Japanese such as desu and masu indicate that a possible unit of the current speaker's turn has already completed; the hearer can start the next turn as soon as he recognizes these utterance-final elements. The subjects in the experiments rate overlapping utterance pairs according to the degree of their interruptiveness. The utterance pairs are constructed so as to involve various overlap timings by manipulating the starting points of the second utterances in the pairs. The experiment 1 shows that overlaps at utterance-final elements are less interruptive than those before utterance-final elements. The experiment 2 shows that the degree of the interruptiveness decreases as the starting point of the overlap become later in an utterance-final element, but the declination becomes moderate when the starting point come to the middle of the utterance-final element. These results sugest that the hearer can start his turn without interrupting the current speaker soon after he recognizes utterance-final elements, which serve as ‘retrospective’ indication of a possible completion of the current speaker's turn.
