CONCURRENT VOWEL IDENTIFICATION .2. EFFECTS OF PHASE, HARMONICITY, AND TASK

Subjects identified concurrent synthetic vowel pairs in four experimen ts. The first experiment found that improvements in vowel identificati on with a difference in fundamental frequency (Delta F-0) do not depen d on component phase. The second investigated more precisely whether p hase patterns resulting from ongoing phase shifts in inharmonic stimul i can by themselves produce effects similar to those attributed to dif ferences in harmonic state of component vowels. No such effects were f ound. The third experiment found that identification was better for ha rmonic than for inharmonic backgrounds, and that it did not depend on target harmonicity. The first three experiments employed a task in whi ch subjects were free to report one or two vowels for each stimulus. T he fourth experiment reproduced several conditions with a more classic task in which subjects had to report two vowels. Compared to the clas sic task, the new task gave larger effects and provided an additional measure of segregation: the number of vowels reported per stimulus. Ov erall, results were consistent with the hypothesis that the auditory s ystem segregates targets by a mechanism of harmonic cancellation of co mpeting vowels. They did not support the hypothesis of harmonic enhanc ement of targets. The lack of a phase effect places strong constraints on models that exploit pitch period asynchrony (PPA) or beats. (C) 19 97 Acoustical Society of America.