Declination of fundamental frequency in speakers' production of parenthetical and main clauses.

An experimental study was conducted to investigate fundamental frequency (F0) contours in sentences with and without parenthetical clauses. Sentences consisted of a systematically lengthened parenthetical clause inserted between the subject noun phrase and the verb phrase of the main clause. The middle portion of the parenthetical was lengthened incrementally in each sentence to test the effects of sentence length on fundamental frequency contours of seven test sentences. Computer-aided measurements were made for: F0 peaks of key stressed segments; duration of the main clause, parenthetical clause, and clause-final syllables within each; and pauses immediately preceding and following the parenthetical. Mean results demonstrate: (1) a drop in F0 for the parenthetical clause, well below the main clause declination and forming a separate contour of declination; (2) a sharp rise in F0 on return to the main clause; (3) no effect of longer parenthetical length on final segment durations of either the parenthetical or the main clause; and (4) no effect of increased parenthetical length on main clause duration or pause length. These results suggest that parenthetical clauses are mentally programmed as independent constituents, but are subject to some of the same general declination constraints as main clauses.