Biomedical subjects

Ward R Drennan

Publications and source records attributed to Ward R Drennan.

4 recordsLinked to original sources

PubMed2006

Current-level discrimination in the context of interleaved, multichannel stimulation in cochlear implants: effects of number of stimulated electrodes, pulse rate, and electrode separation.

The ability of cochlear implantees to detect an increment in current level at one of many stimulated electrodes was investigated. Such changes in the electric profile provide information for cochlear implantees to discriminate numerous sounds, especially vowels. In Experiment 1, sensitivity to increases in current level at one stimulation site in the electric profile decreased as the number of stimulated electrodes increased. This outcome was most likely a result of decreased stimulus levels at individual electrodes that were required to retain a comfortable loudness when the number of active electrodes was increased. Experiment 2 investigated the effects of pulse rate and separation between stimulation sites when the levels in percent of dynamic range and number of stimulated electrodes were held constant. The effect of pulse rate and electrode separation varied among listeners. The sensitivity of 6 of 9 listeners was best at the pulse rate that they used clinically. This might have been the result of adaptation to the clinical pulse rate, or listeners might have chosen their inherently best pulse rate during the clinical fitting.

Adult↗

PubMed2005

Current-level discrimination using bipolar and monopolar electrode configurations in cochlear implants.

This study examined current-level discrimination ability in listeners with cochlear implants using bipolar and monopolar electrode configurations. Current-level discrimination ability was measured as a function of electrode configuration (monopolar and bipolar), stimulation site (8 and 16) and level (5%, 15%, 25%, 50% and 80% of the dynamic range). Weber fractions usually decreased with increasing level. Differences in Weber fractions between monopolar and bipolar configurations were observed for listeners with short durations of deafness (<5 years). For these listeners, in the bipolar condition at the more-apical site 16, Weber fractions remained constant with increasing level, and the Weber fractions at low levels were smaller than in other conditions. We suggest that nerve density was better and the nerve-to-site-of-action-potential distance was smaller in these cases such that more fibers could be recruited with a unit increase in current level, leading to better current-level sensitivity.

Adult↗

PubMed2005

Localization and speech-identification ability of hearing-impaired listeners using phase-preserving amplification.

OBJECTIVE: The purpose of these experiments was to determine the ability of hearing-impaired listeners to localize and to identify speech in noise using phase-preserving and non-phase-preserving amplification. DESIGN: These abilities were measured 4 times over each of two 16-week periods, using a randomized, single-blinded, within-subject crossover design. Listeners were fitted bilaterally, using the National Acoustic Laboratories linear frequency-gain characteristic with a digital hearing aid programmed in one of two ways: (1) with a linear-phase filter and (2) with filters designed to compensate for the magnitude and phase anomalies caused by the hearing aid fitting, thus preserving interaural phase. Listeners identified a word and its location in background noise with a speech-shaped spectrum. RESULTS: Immediately after fitting, both hearing aid programs reduced the listeners' ability to localize the speech in noise. The phase-preserving processing had a less detrimental effect on localization ability immediately after fitting. After 3 weeks, performance improved such that, for localization in noise, there was no detrimental effect of amplification and no difference between the two processing strategies. Over 16 weeks, speech understanding in noise improved. Speech understanding for phase-preserving processing was slightly and significantly better than linear-phase processing at 16 weeks. CONCLUSIONS: Localization ability using phase-preserving amplification does not differ from localization ability using traditional non-phase-preserving amplification after just 3 weeks of use. Listeners quickly acclimated to altered spatial cues. Phase-preserving amplification provided a 2.3% advantage for speech intelligibility in noise after 16 weeks.

Aged↗

PubMed2003

Perceptual segregation of competing speech sounds: the role of spatial location.

Culling and Summerfield [J. Acoust Soc. Am. 92, 785-797 (1995)] showed that listeners could not use ongoing interaural time differences (ITDs) to achieve source segregation. The present experiments tested a free-field analog of their experiment. The stimuli consisted of narrow bands of noise, pairs of which represented the first and second formants of the whispered vowels "ar," "ee," "er," and "oo." A target noise-band pair (vowel) was presented at various angles on the listeners' left while a complementary distracter was presented on the listeners' right. Listeners correctly identified the target vowel in the free-field well above chance. Performance remained well above chance in headphone experiments that retained spatial cues but eliminated reverberations and head movements. The full range of cues that normally determine perceived spatial location provided sufficient information for segregation. Further experiments, which systematically evaluated the contribution of these cues in isolation and in combination, showed that some listeners, following training, exhibited the ability to segregate based on ongoing ITDs alone. Substantial individual differences were observed. The results show that listeners can use spatial cues to segregate simultaneous sound sources.

Adolescent↗