Functional clauses and sentence segmentation

In two experiments subjects listened to a sentence containing a brief tone, then wrote out the sentence and marked the location of the tone. The experimental sentences were biclausal with the tone placed before or after the clause break. The initial clause was either functionally complete or functionally incomplete. Functionally complete clauses contain a complete set of fully specified grammatical relations, while functionally incomplete clauses do not. In Experiment 1 tones were mislocated toward the clause break and the final word of the first clause significantly more often for functionally complete clauses. Experiment 2 replicated this finding holding deep- and surface-structure variables constant. The results indicate that functionally complete clauses are better segmentation units during sentence perception than functionally incomplete clauses. Purely structural theories of the units of sentence perception cannot account for this finding.