Many competing noises in real environments are modulated or fluctuating in level. Listeners with normal hearing are able to take advantage of temporal gaps in fluctuating maskers. Listeners with sensorineural hearing loss show less benefit from modulated maskers. Cochlear implant users may be more adversely affected by modulated maskers because of their limited spectral resolution and by their reliance on envelope-based signal-processing strategies of implant processors. The current study evaluated cochlear implant users' ability to understand sentences in the presence of modulated speech-shaped noise. Normal-hearing listeners served as a comparison group. Listeners repeated IEEE sentences in quiet, steady noise, and modulated noise maskers. Maskers were presented at varying signal-to-noise ratios (SNRs) at six modulation rates varying from 1 to 32 Hz. Results suggested that normal-hearing listeners obtain significant release from masking from modulated maskers, especially at 8-Hz masker modulation frequency. In contrast, cochlear implant users experience very little release from masking from modulated maskers. The data suggest, in fact, that they may show negative effects of modulated maskers at syllabic modulation rates (2-4 Hz). Similar patterns of results were obtained from implant listeners using three different devices with different speech-processor strategies. The lack of release from masking occurs in implant listeners independent of their device characteristics, and may be attributable to the nature of implant processing strategies and/or the lack of spectral detail in processed stimuli.

The discriminability of bilabial stop consonants differing in VOT (the Abramson-Lisker bilabial series) was measured in a same-different task, an oddity task, and a dual response, discrimination--identification task. Subjects showed excellent within-category discrimination in all three tasks after a moderate amount of training in a same-different task with a fixed standard and with feedback. In addition, discrimination performance continuously improved with increasing stimulus difference for both intra- and intercategory comparisons. Also, subjects were able to alter their identification responses so that well-defined category boundaries fell at arbitrary values determined by the experiments. These results are not compatible with a strict interpretation of the categorical perception of stop consonants.

Based on the findings of this study, when auditory and visual integration of speech information fails to occur, producing a nonfused response, participants select an alternative response from the modality with the least ambiguous signal.

This study examined the variables that contribute to the large individual differences in the speech perception skills of children with the Nucleus multichannel cochlear implant. Sixty-one children were tested on four measures of speech perception: two tests of closed-set word recognition, one test of open-set recognition of phrases, and one open-set monosyllabic word test, scored on the basis of the percentage of phonemes as well as words identified correctly. The results of a series of multiple regression analyses revealed that the variables of processor type, duration of deafness, communication mode, age at onset of deafness, length of implant use, and age implanted accounted for roughly 35% of the variance on two tests of closed-set word recognition, and 40% of the variance on measures that assessed recognition of words or phonemes in an open set. Length of implant use accounted for the most variance on all of the speech perception measures.

The purpose of this investigation was to determine whether children with normal linguistic skills demonstrate increasing developmental changes in their perception of place of articulation for stop consonants with short- and long-duration formant transitions. Three experimental paradigms were used with children and adults: discrimination, labeling, and selective adaptation. Two sets of synthetic CV syllables, varying along a seven-step, bilabial-to-alveolar dimension, were used as stimuli. These two synthetic continua differed in the length of the second and third formant transitions. Results showed that children's discrimination abilities gradually approximated those of adults, but did not reach adult levels even at 10 years of age. Differences were not observed in the labeling task. Further, results of the selective adaptation task indicated that only the adult subjects showed a significant boundary shift for any adapting stimuli. The absence of selective adaptation in children was interpreted as a possible reflection of their poorer auditory abilities. Thus, the pattern of speech perception development for children for place of articulation is a complex one with a strong auditory developmental component.