Biomedical subjects

Christopher W Turner

Publications and source records attributed to Christopher W Turner.

8 recordsLinked to original sources

PubMed2006

Hearing loss and the limits of amplification.

This review article summarizes the effects of sensorineural hearing loss on the recognition of amplified speech, both for speech presented in quiet and in a noise background. Some hypotheses are presented regarding the underlying damage in the cochlea that leads to the deficits in speech recognition for hearing losses of various configurations. For severe hearing losses in the high frequencies, amplification is often ineffective. While the existing data also suggest that sensorineural hearing loss can lead to poor frequency resolution, which leads to problems understanding speech in noise, the frequency resolution of the cochlear implant is usually even poorer. Therefore a strategy of preserving low-frequency residual hearing combined with electrical stimulation for the higher frequencies is an attractive solution for patients with severe high-frequency hearing loss.

Audiometry, Pure-Tone↗

PubMed2006

Stability of low-frequency residual hearing in patients who are candidates for combined acoustic plus electric hearing.

The purpose of this study was to investigate the stability over time of low-frequency auditory thresholds to better determine if the new technique of using a short-electrode cochlear implant that preserves residual low-frequency acoustic hearing can be a long-term solution for those with severe-to-profound hearing loss at high frequencies. The present study determined the long-term rate of decline in acoustic hearing in patients who have a preexisting hearing loss yet have not been implanted with a cochlear implant. A retrospective analysis of patients' audiograms that fit into the range for candidacy for the short-electrode device was performed to calculate the rate of change of threshold over time. The analysis of adult patients' data indicated that there was an average of only 1.05 dB hearing deterioration per year in the low frequencies and that presbycusis accounted for approximately one third to one half of this decline. The average deterioration of hearing threshold for pediatric patients was 1.2 dB per year; however, the rates of change in pediatric patients were considerably more variable (across individuals and across frequencies) than in adults. These data provide support for the idea that the short-electrode cochlear implant may be a practical solution for most adults in the long run, but this may not be the case for all pediatric patients.

Acoustic Stimulation↗

PubMed2006

Pure-tone auditory stream segregation and speech perception in noise in cochlear implant recipients.

This study examined the ability of cochlear implant users and normal-hearing subjects to perform auditory stream segregation of pure tones. An adaptive, rhythmic discrimination task was used to assess stream segregation as a function of frequency separation of the tones. The results for normal-hearing subjects were consistent with previously published observations (L.P.A.S van Noorden, Ph.D. dissertation, Eindhoven University of Technology, Eindhoven, The Netherlands 1975), suggesting that auditory stream segregation increases with increasing frequency separation. For cochlear implant users, there appeared to be a range of pure-tone streaming abilities, with some subjects demonstrating streaming comparable to that of normal-hearing individuals, and others possessing much poorer streaming abilities. The variability in pure-tone streaming of cochlear implant users was correlated with speech perception in both steady-state noise and multi-talker babble. Moderate, statistically significant correlations between streaming and both measures of speech perception in noise were observed, with better stream segregation associated with better understanding of speech in noise. These results suggest that auditory stream segregation is a contributing factor in the ability to understand speech in background noise. The inability of some cochlear implant users to perform stream segregation may therefore contribute to their difficulties in noise backgrounds.

Adult↗

PubMed2005

Spectral peak resolution and speech recognition in quiet: normal hearing, hearing impaired, and cochlear implant listeners.

Spectral peak resolution was investigated in normal hearing (NH), hearing impaired (HI), and cochlear implant (CI) listeners. The task involved discriminating between two rippled noise stimuli in which the frequency positions of the log-spaced peaks and valleys were interchanged. The ripple spacing was varied adaptively from 0.13 to 11.31 ripples/octave, and the minimum ripple spacing at which a reversal in peak and trough positions could be detected was determined as the spectral peak resolution threshold for each listener. Spectral peak resolution was best, on average, in NH listeners, poorest in CI listeners, and intermediate for HI listeners. There was a significant relationship between spectral peak resolution and both vowel and consonant recognition in quiet across the three listener groups. The results indicate that the degree of spectral peak resolution required for accurate vowel and consonant recognition in quiet backgrounds is around 4 ripples/octave, and that spectral peak resolution poorer than around 1-2 ripples/octave may result in highly degraded speech recognition. These results suggest that efforts to improve spectral peak resolution for HI and CI users may lead to improved speech recognition.

Acoustic Stimulation↗

PubMed2004

Speech recognition in noise for cochlear implant listeners: benefits of residual acoustic hearing.

The purpose of this study was to explore the potential advantages, both theoretical and applied, of preserving low-frequency acoustic hearing in cochlear implant patients. Several hypotheses are presented that predict that residual low-frequency acoustic hearing along with electric stimulation for high frequencies will provide an advantage over traditional long-electrode cochlear implants for the recognition of speech in competing backgrounds. A simulation experiment in normal-hearing subjects demonstrated a clear advantage for preserving low-frequency residual acoustic hearing for speech recognition in a background of other talkers, but not in steady noise. Three subjects with an implanted "short-electrode" cochlear implant and preserved low-frequency acoustic hearing were also tested on speech recognition in the same competing backgrounds and compared to a larger group of traditional cochlear implant users. Each of the three short-electrode subjects performed better than any of the traditional long-electrode implant subjects for speech recognition in a background of other talkers, but not in steady noise, in general agreement with the simulation studies. When compared to a subgroup of traditional implant users matched according to speech recognition ability in quiet, the short-electrode patients showed a 9-dB advantage in the multitalker background. These experiments provide strong preliminary support for retaining residual low-frequency acoustic hearing in cochlear implant patients. The results are consistent with the idea that better perception of voice pitch, which can aid in separating voices in a background of other talkers, was responsible for this advantage.

Adult↗

PubMed2003

Combining acoustic and electrical hearing.

OBJECTIVES/HYPOTHESIS: The concept of combining electrical stimulation for high-frequency sound with acoustic hearing for low-frequency information was tested. In addition, whether residual hearing can be preserved when an electrode is placed into the inner ear up to 10 mm and whether place of electrical stimulation influences speech perception were tested. STUDY DESIGN: A single-subject clinical trial design was employed. METHODS: Six postlingual adults with severe high-frequency hearing impairment were recruited to participate in the study. A new six-channel cochlear implant was designed for the clinical trial. The intracochlear electrodes were either 6 or 10 mm in length based on a Nucleus CI-24 multichannel implant. Monosyllabic word understanding and consonant identification testing in a recorded sound-only condition were used to assess changes in speech perception. Follow-up was greater than 12 months. RESULTS: Acoustic hearing was preserved in all six subjects (n = 3, 6-mm electrodes; n = 3, 10-mm electrodes). Preoperative monosyllabic word and sentence scores were unchanged in all subjects following implantation. A 30% to 40% improvement in consonant recognition occurred with the 10-mm electrode. The subjects with 10-mm electrodes were able to understand 83% to 90% of the monosyllabic words using the implant plus binaural hearing aids. Scores were more than doubled when compared with preoperative scores with hearing aids only. CONCLUSION: The human ear has the capability to integrate both acoustic and high-frequency electrically processed speech information. Placement of a short, 10-mm electrode does not appear to damage residual low-frequency inner ear hair cell function, interfere with the micro mechanics of normal cochlear vibration, or decrease residual speech perception. The improvement in speech recognition was due primarily to the increased perception of higher-frequency consonantal speech cues, and this improvement took several months to become apparent. Such a device can provide a substantial benefit in speech understanding to individuals with severe high-frequency hearing loss, while still maintaining the benefits of the residual lower-frequency acoustic hearing. The position of the electrode and the place of frequency information within the cochlea were shown to be important factors in the success of such a device.

Cochlear Implants↗

PubMed2003

The resolution of complex spectral patterns by cochlear implant and normal-hearing listeners.

The differences in spectral shape resolution abilities among cochlear implant (CI) listeners, and between CI and normal-hearing (NH) listeners, when listening with the same number of channels (12), was investigated. In addition, the effect of the number of channels on spectral shape resolution was examined. The stimuli were rippled noise signals with various ripple frequency-spacings. An adaptive 41FC procedure was used to determine the threshold for resolvable ripple spacing, which was the spacing at which an interchange in peak and valley positions could be discriminated. The results showed poorer spectral shape resolution in CI compared to NH listeners (average thresholds of approximately 3000 and 400 Hz, respectively), and wide variability among CI listeners (range of approximately 800 to 8000 Hz). There was a significant relationship between spectral shape resolution and vowel recognition. The spectral shape resolution thresholds of NH listeners increased as the number of channels increased from 1 to 16, while the CI listeners showed a performance plateau at 4-6 channels, which is consistent with previous results using speech recognition measures. These results indicate that this test may provide a measure of CI performance which is time efficient and non-linguistic, and therefore, if verified, may provide a useful contribution to the prediction of speech perception in adults and children who use CIs.

Adult↗

PubMed2002

Benefits of amplification for speech recognition in background noise.

The purpose of the present study was to examine the benefits of providing audible speech to listeners with sensorineural hearing loss when the speech is presented in a background noise. Previous studies have shown that when listeners have a severe hearing loss in the higher frequencies, providing audible speech (in a quiet background) to these higher frequencies usually results in no improvement in speech recognition. In the present experiments, speech was presented in a background of multitalker babble to listeners with various severities of hearing loss. The signal was low-pass filtered at numerous cutoff frequencies and speech recognition was measured as additional high-frequency speech information was provided to the hearing-impaired listeners. It was found in all cases, regardless of hearing loss or frequency range, that providing audible speech resulted in an increase in recognition score. The change in recognition as the cutoff frequency was increased, along with the amount of audible speech information in each condition (articulation index), was used to calculate the "efficiency" of providing audible speech. Efficiencies were positive for all degrees of hearing loss. However, the gains in recognition were small, and the maximum score obtained by an listener was low, due to the noise background. An analysis of error patterns showed that due to the limited speech audibility in a noise background, even severely impaired listeners used additional speech audibility in the high frequencies to improve their perception of the "easier" features of speech including voicing.

Audiometry, Pure-Tone↗