Effects of frequency-shifted auditory feedback on fundamental frequency of long stressed and unstressed syllables

Twenty-four normally speaking subjects had to utter the test word /tatatas/ with different stress patterns repeatedly. Auditory feedback was provided by head-phones and was shifted downwards in frequency during randomly selected trials while the subjects were speaking the complete test word. If the first syllable was long stressed, fundamental frequency of the vowel significantly increased by 2 Hz (corresponding to 25.5 cents) under frequency-shifted auditory feedback of .5 octave downwards, whereas under a shift of one semitone downwards a trend of an increase could be observed. If the first syllable was unstressed, fundamental frequency remained unaffected. Regarding the second syllable, significant increases or a trend for an increase of fundamental frequency was found in both shifting conditions. Results indicate a negative feedback mechanism that controls the fundamental frequency via auditory feedback in speech production. However, within a syllable a response could be found only if the syllable duration was long enough. Compensation for frequency-shifted auditory feedback still is quite imperfect. It is concluded that control of fundamental frequency is rather important on a suprasegmental level.