Although segregation of both simultaneous and sequential speech items may be involved in the reception of speech in noisy environments, research on the latter is relatively sparse. Further, previous studies examining the ability of hearing-impaired listeners to form distinct auditory streams have produced mixed results. Finally, there is little work investigating streaming in cochlear implant recipients, who also have poor frequency resolution. The present study focused on the mechanisms involved in the segregation of vowel sequences and potential limitations to segregation associated with poor frequency resolution. An objective temporal-order paradigm was employed in which listeners reported the order of constituent vowels within a sequence. In Experiment 1, it was found that fundamental frequency based mechanisms contribute to segregation. In Experiment 2, reduced frequency tuning often associated with hearing impairment was simulated in normal-hearing listeners. In that experiment, it was found that spectral smearing of the vowels increased accurate identification of their order, presumably by reducing the tendency to form separate auditory streams. These experiments suggest that a reduction in spectral resolution may result in a reduced ability to form separate auditory streams, which may contribute to the difficulties of hearing-impaired listeners, and probably cochlear implant recipients as well, in multi-talker cocktail-party situations.

A system of 36 impinging microjets was implemented on a round jet of Mach number 0.9, and the noise reduction was studied as a function of the microinjection mass flux, the number of microjets blowing, the layout of the blowing microjets, and the microjet diameter. Depending on the microinjection flux parameters, overall jet-noise reduction varied from 0 to 1.5 dB, showing some nonmonotonic behavior due to the change between subsonic to supersonic microjet regimes. The study of the microjet layout showed that the noise reduction decreased when the microjets were too close to each other and that certain configurations of microjet pairs could be favorable; this can be related to the flow structures induced by the microjets. Spectral analysis disclosed different control mechanisms, with highfrequency regeneration for high-injection flux, local control behavior at midfrequencies, and global behavior at low frequencies.

Cochlear-implant ͑CI͒ users often have difficulties perceiving speech in noisy environments. Although this problem likely involves auditory scene analysis, few studies have examined sequential segregation in CI listening situations. The present study aims to assess the possible role of fundamental frequency ͑F 0 ͒ cues for the segregation of vowel sequences, using a noise-excited envelope vocoder that simulates certain aspects of CI stimulation. Obligatory streaming was evaluated using an order-naming task in two experiments involving normal-hearing subjects. In the first experiment, it was found that streaming did not occur based on F 0 cues when natural-duration vowels were processed to reduce spectral cues using the vocoder. In the second experiment, shorter duration vowels were used to enhance streaming. Under these conditions, F 0 -related streaming appeared even when vowels were processed to reduce spectral cues. However, the observed segregation could not be convincingly attributed to temporal periodicity cues. A subsequent analysis of the stimuli revealed that an F 0 -related spectral cue could have elicited the observed segregation. Thus, streaming under conditions of severely reduced spectral cues, such as those associated with CIs, may potentially occur as a result of this particular cue.

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