| Summary: | Previous research (Scheffers, 1983) has indicated that differences in the fundamental frequencies (F(,0)s) of the two simultaneous components in a vowel mixture facilitate the perceptual separation of the vowels. Experiments 1, 2, and 3 were an extension of that work using simultaneous synthesized vowels. They investigated (a) the effects of using vowels with gliding F(,0)s, and (b) the effects of using crossing versus parallel glides. The results indicated that perceptual separation was better when the mixture contained gliding vowels than when it contained steady state ones. In addition, it was found that the separation effect was even stronger when the glides were crossing as compared to being parallel. Experiment 4 investigated the role of formant peaks in vowel identification by employing a vowel mixed with a simultaneous pulse train masker. It was found that the vowel was better identified when the masker was a gliding pulse train as compared to a steady state one. In Experiments 5, 6, and 7 mixtures of unfiltered and filtered (high- and low-pass) pulse trains were used with steady state and gliding F(,0)s and different F(,0) separations. The results indicated that increased F(,0) differences and the use of glides facilitate the perceptual separation of simultaneous sounds. The superior effect of the crossing glides can be explained in terms of the common frequency modulation of the harmonics in each subset (component of the mixture) and the subsequent decorrelation of the harmonics in the two subsets. The type of filtering used had no apparent effect indicating that separation was possible for high-pass filtered pulse trains, probably based on periodicity (timing) information. These findings were discussed in terms of mechanisms of processing.
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