Repairing inappropriately specified utterances : Revision or restart?

In two experiments, we investigated repair of inappropriately specified utterances (e.g., blue square instead of dark blue square) to determine whether speakers can simply revise a speech plan or must begin anew. In Experiment 1, speakers produced a prime utterance followed by a target utterance that differed from the prime in only one word, but in Experiment 2, they only planned the prime but produced the target. If speakers must repair by restarting, both situations would involve planning from scratch, with a possible benefit of residual activation. If they can repair by revising, though, only the first situation would involve planning from scratch, and the second situation would involve revision of a plan. The targets had either one word more (addition) or fewer (deletion) than the prime sentences. The restart hypothesis predicted that any cost of addition over deletion should be similar in the two experiments. In contrast, the revision hypothesis predicted an extra cost of addition in Experiment 2, because addition involves retrieval of an extra word. In support of the revision hypothesis, there was no difference between additions and deletions in Experiment 1, but in Experiment 2 additions took longer than deletions. We conclude that speakers can repair utterances by revising a speech plan.