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Biomedical subjects

M W Lowder

Publications and source records attributed to M W Lowder.

15 recordsLinked to original sources
PubMed2001

A longitudinal study of electrode impedance, the electrically evoked compound action potential, and behavioral measures in nucleus 24 cochlear implant users.

OBJECTIVE: The primary goal of this study was to examine changes that may occur in electrode impedance, electrically evoked compound action potential (EAP) threshold and slope of the EAP growth function, and behavioral measures of threshold T-level) and maximum comfort (C-level) over time in both adult and child cochlear implant users. Secondary goals were to determine whether changes in these measures are consistent between children and adults, and to determine whether behavioral measures (MAP T- and C-levels) and electrophysiologic measures (EAP thresholds) exhibit the same trends over time. DESIGN: Thirty-five children and 33 adults implanted with the Nucleus CI24M between November 1996 and August 1999 participated in this study. Subjects were included in this study if 1) they had used their implant for at least 1 yr after device connection, and 2) they had participated in the necessary data collection at a minimum number of the time intervals assessed in this study. EAP threshold, slope of the EAP growth function, and common ground electrode impedance measures were collected intraoperatively, at initial stimulation, and at several subsequent visits up to 2 yr post initial stimulation. MAP T- an d C-levels weremeasured at initial stimulation and at the same time intervals as described above. RESULTS: Changes in electrode impedance, EAP thresholds, and slope of the EAP growth function from measures made intraoperatively, at initial stimulation, and at 1 to 2 mo post initial stimulation were similar in both children and adults. Beyond the 1- to 2-mo visit, children exhibited significant increases in electrode impedance, EAP thresholds, slope, and MAP T-levels, whereas these samemeasures in adults remained relatively stable. EAP thresholds in children stabilized by the 3- to 8-mo visit, and electrode impedance stabilized by the 6- to 8-mo visit, while slope of the EAP growth function, MAP T-levels,and MAP C-levels werestable by 1 yr post initial stimulation. C-levels in adults increased up to 1 yr post initial stimulation; however, the amount of increase was much smaller than that seen in children. In both children and adults, longitudinal trends in EAP thresholds mirrored T-level more closely than C-level. CONCLUSIONS: The results of this study suggest that peripheral changes occur in many children that do not generally occur in adults within the first year of cochlear implant use. One implication of these results is that if EAP thresholds are to be used to assist in programming the speech processor for children, it is best to make those measures at the same time interval as device programming rather than using measures made intraoperatively or at the initial programming session to set MAP levels at later visits.

Acoustic Impedance Tests↗
PubMed1998

Speech perception performance in experienced cochlear-implant patients receiving the SPEAK processing strategy in the Nucleus Spectra-22 cochlear implant.

Sixteen experienced cochlear implant patients with a wide range of speech-perception abilities received the SPEAK processing strategy in the Nucleus Spectra-22 cochlear implant. Speech perception was assessed in quiet and in noise with SPEAK and with the patients' previous strategies (for most, Multipeak) at the study onset, as well as after using SPEAK for 6 months. Comparisons were made within and across the two test sessions to elucidate possible learning effects. Patients were also asked to rate the strategies on seven speech recognition and sound quality scales. After 6 months' experience with SPEAK, patients showed significantly improved mean performance on a range of speech recognition measures in quiet and noise. When mean subjective ratings were compared over time there were no significant differences noted between strategies. However, many individuals rated the SPEAK strategy better for two or more of the seven subjective measures. Ratings for "appreciation of music" and "quality of my own voice" in particular were generally higher for SPEAK. Improvements were realized by patients with a wide range of speech perception abilities, including those with little or no open-set speech recognition.

Adult↗
PubMed1998

Single-channel to multichannel conversions in adult cochlear implant subjects.

OBJECTIVE: This study aimed to compare open-set speech perception of single-channel with multichannel cochlear implants in the same ear of postlingually deafened adults. STUDY DESIGN: The study design was a retrospective case and literature review. SETTING: The study was conducted at a tertiary referral center with an associated veterans administration hospital. PATIENTS: Postlingually deafened adults with at least 6 months of experience with a single-channel cochlear implant were studied. INTERVENTION: Replacement of a single-channel with a multichannel cochlear implant in the same ear was performed. MAIN OUTCOME MEASURES: Open-set word and sentence perception scores at least 6 months after single-channel implantation and multichannel reimplantation were measured. RESULTS: Six of six patients had substantial improvement in open-set speech recognition after reimplantation of the same ear. CONCLUSIONS: Removal of a functioning single-channel implant and replacement with a multichannel device are appropriate in postlingually deafened adults who desire better speech recognition.

Adult↗
PubMed1997

Performance over time of adult patients using the Ineraid or nucleus cochlear implant.

This study examined the average and individual performance over time of 49 adult cochlear implant subjects. Subjects were randomly assigned to receive either the Ineraid cochlear implant, with analog processing, or the Nucleus cochlear implant, with feature-extraction processing. All subjects had postlingual profound bilateral sensorineural hearing loss and received no significant benefit from hearing aids before implantation. Group data were examined in two ways. First, only subjects who had complete data over the test period were examined. Second, an analysis of all available data was carried out by mixed linear-model analysis. In this analysis, to account for missed follow-ups at the planned intervals, data consisting of the observations closest in time to the planned test times were modeled by natural splines with knots at the planned follow-up times. Contrasts between all pairs of planned follow-up times for each device were tested, as were contrasts between devices at each planned follow-up time. Results indicated little difference between the performance of the Ineraid and Nucleus subjects in their level of performance or their rate of learning. Postimplantation performance was typically superior to preimplantation performance within 9 months, and continued to improve up to 18-30 months depending on the speech perception measure. In some subjects, improvements in speech perception measures were observed up to four or five years postimplantation. There was also evidence that three subjects had a decrement in overall speech perception performance, although their postimplantation scores were always higher than their preimplantation scores. In at least one subjects this was likely a result of age-related cognition decrements.

Adult↗
PubMed1997

Speech perception by prelingually deaf children and postlingually deaf adults with cochlear implant.

We review recent data from the University of Iowa obtained from prelingually deaf children over 3 years using feature-extraction versions of the Nucleus cochlear implant, and from postlingually deaf adults using the compressed-analog Ineraid, a feature-extraction version of Nucleus, and a continuous interleaved sampling version of the Clarion cochlear implant. Both adults and children were followed over a 3-year period. Average results are shown where each patient is represented at each point in time. Results for the children show continued improvement over the 3-year period, with some children obtaining maximum scores possible on the easier closed-set tests. Substantial improvements in audiovisual enhancement were provided by the cochlear implant. Results from the adults show maximum gains within the first year of implant use, although some patients show continued improvements after 2 years of implant use. Adults who have been deaf for several years and who receive their implant when they are older tend not to perform as well as adults who have been deaf for only a few years or receive their implant when they are younger.

Adult↗
PubMed1996

A within-subject comparison of adult patients using the Nucleus F0F1F2 and F0F1F2B3B4B5 speech processing strategies.

This study compares the Nucleus F0F1F2 and F0F1F2B3B4B5 (also known as "Multipeak") of "Mpeak") processing schemes in 17 patients wearing the Mini Speech Processor. All patients had at least 18 months implant experience using the F0F1F2 processing strategy. For this study, they were switched to the F0F1F2B3B4B5 processing strategy for 3 months. They then returned to using the F0F1F2 strategy for 3 months, then used the F0F1F2B3B4B5 strategy again for 3 months, and lastly used the F0F1F2 strategy for 3 months. Performance' was evaluated with both schemes after each interval, using speech recognition tests and subjective ratings. Overall, differences between the results for the two processing schemes were not large. Average performance was somewhat better for the F0F1F2B3B4B5 strategy for word and sentence identification, but not for any of the other speech measures. Superior performance was observed in 8 patients with the F0F1F2B3B4B5 strategy. However, 6 of the 8 individuals were significantly better on only one of the six speech measures in the test battery. The other 2 patients performed better on two of the speech measures. Superior performance was also observed in 3 patients with F0F1F2 strategy for consonant recognition. For the remaining patients, there was little difference in their performance with the two strategies. Information transmission analyses indicated that the F0F1F2B3B4B5 strategy transmitted consonant duration and frication cues more efficiently than F0F1F2. Experience with one strategy appeared to benefit performance with the other strategy.

Adult↗
PubMed1996

Initial independent results with the Clarion cochlear implant.

OBJECTIVE: This paper reports some preliminary findings from patients, implanted at the University of Iowa, using the Advanced Bionics Clarion cochlear implant (version 1.0). We compared the performance of patients using both simultaneous analog and nonsimultaneous pulsatile processing strategies. The performance of Clarion patients was also compared with a group of patients who were using either the feature-extraction Nucleus cochlear implant or the compressed-analog Ineraid cochlear implant. DESIGN: One aim was to compare the analog and pulsatile stimulation in 19 patients using the Clarion implant. This aim could be accomplished only partially because of difficulties encountered in adequately fitting patients with the analog strategy. A second aim was to compare the Clarion users' performance with feature-extraction Nucleus and compressed-analog Ineraid patients. Comparisons were made with all patients having 9 mo experience postimplantation. RESULTS: Subjects performed better using the pulsatile mode compared with the analog mode. All subjects chose to use the pulsatile strategy after the first 3 mo of the study. Results comparing performance at 9 mo with our compressed-analog Ineraid and feature-extraction Nucleus patients indicated, in general, better average performance for the Clarion users. CONCLUSIONS: We conclude that the pulsatile version of the Clarion cochlear implant typically produces superior performance to the analog version of that device at this stage in its development. After 9 mo of experience, users of the Clarion implant are performing better than are users of the feature-extraction Nucleus and compressed-analog Ineraid cochlear implants with comparable amounts of experience.

Adult↗
PubMed1992

Audiological management and performance of adult cochlear-implant patients.

We review the signal-processing strategies of three of the most common cochlear implants in use today, the single-channel House, the multichannel Nucleus, and the Ineraid devices. The results of 65 postlinguistically-deafened patients tested at The University of Iowa are reviewed. The tests include everyday sound, accent, word and sentence recognition, as well as noise/voice differentiation. For all tests, patients with the Nucleus and Ineraid cochlear implants outperformed those with the House implant. In general, selection criteria should focus on comparing the performance of Patients who have already received an implant. Prelinguistically-deafened adults are typically not good cochlear-impact candidates. Cochlear-implant teams should be aware of the enormous time commitment for testing and rehabilitation of these patients, and be prepared to handle frequent implant breakdowns. Nevertheless, cochlear-implant patients have been helped significantly be these devices.

Audiology↗
PubMed1989

Audiologic results following reimplantation of cochlear implants.

Five patients using cochlear implants experienced internal device failure 6 weeks to 4 years following implantation. All devices were removed and new electrodes inserted. Single-channel implants were replaced with multichannel systems in three patients, while the others received identical multichannel implants. The performance on a uniform battery of audiologic tests was the same or better with the second implant in all patients. Replacement of intracochlear electrodes did not induce clinically apparent degeneration of auditory performance in this series.

Adolescent↗
PubMed1985

Iowa cochlear implant clinical project: results with two single-channel cochlear implants and one multi-channel cochlear implant.

Cochlear implants have become a realistic alternative for the management of profoundly deaf patients. A variety of implants with differing electrode designs and coding strategies have been developed by nine major implant centers around the world. Each center has their "star" patient, but objective comparisons between these different implant designs are unavailable. In order to determine the performance characteristics of the present generation of cochlear implants, comparison data are vital. We have developed an independent center where uniform objective comparisons of different cochlear implants can be performed longitudinally. This report will present results of nine patients implanted with three different cochlear implant prostheses. Four patients have been implanted with the Los Angeles (House) single-channel implant, three patients have received the Vienna (Hochmair) single-channel intracochlear device, and two patients have been implanted with the Melbourne (Clark) 21-channel unit. All patients have had 11 months or more of experience with their cochlear prostheses. The results of a comprehensive audiologic battery which includes audiovisual and environmental tasks are presented. All implants provide significant improvement in speechreading and sound awareness. The findings to date suggest that there is strong correlation between top-down cognitive processing (as reflected by lip reading skills) and performance with cochlear implants.

Adult↗
PubMed1984

Initial Iowa results with the multichannel cochlear implant from Melbourne.

Two subjects who use the Melbourne multichannel cochlear implant were studied. Live-voice word, consonant, and vowel recognition tests, and a speech-tracking task were administered at regular intervals during the first 90 days after implantation. Results indicated 30-50% correct recognition of vowels (given 9 alternatives) and about 30-60% correct recognition of consonants (given 12 alternatives). Speech tracking showed from two to three times faster rates with the implant and vision compared to a vision-alone condition. After 3-4 months of implant experience, a number of recorded tests from the Minimal Auditory Capabilities battery and the Iowa Cochlear-Implant tests were then administered. These results indicated about 80% recognition of everyday sounds in a five-choice closed-set condition and about 50% recognition of everyday sounds in an open-set condition. The subjects were 50% correct at identifying the accented words in a sentence and about 50% correct at determining the number of syllables in a word. One subject was unable to recognize a sentence as a statement or a question. Background noise (+10 dB S/N) reduced their performance on a four-choice spondee test to chance. Both subjects were able to identify a sound as either a voice or a modulated noise at 95% correct, and both could recognize speaker sex at 95% correct. Neither could discriminate whether two (successive) sentences were spoken by the same speaker or by two different speakers. Remarkably, one subject identified 45% and the other 85% of the words in sentences that were preceded by a contextual picture using sound alone. One subject identified 13% of the words in sentences in sound alone even without contextual information.

Adult↗
PubMed1984

Preliminary assessment of the Los Angeles, Vienna and Melbourne cochlear implants.

We tested four patients using the single-channel cochlear implant from Los Angeles, three patients using the single-channel cochlear implant from Vienna, and two patients using the multichannel cochlear implant from Melbourne. Tests from the MAC battery and the Iowa Cochlear Implant Battery were used. Most patients were able to identify some environmental sounds. Three of the patients had difficulty distinguishing between male and female voices, and three could not distinguish between a noise and a voice. All patients had difficulty discriminating between unknown speakers of the same sex. A four-choice spondee test in noise showed that all patients suffered drastically from background noise. In all cases there was an improvement in lipreading ability with the implant. On a sentence test with a contextual cue seven patients got some words with sound alone. Results obtained with the multichannel implant are superior on several tasks, but we have tested too few patients to allow us any firm conclusions.

Auditory Perception↗
PubMedDate not supplied

Audiological results with two single channel cochlear implants.

We tested six patients with single channel cochlear implants on several tests from the Minimal Auditory Capabilities battery and the Iowa Cochlear Implant Tests. All patients were able to discriminate some everyday sounds and to identify the number of syllables in the words presented. Five patients were able to identify speaker sex reliably. Surprisingly, some patients had difficulty discriminating between a modulated noise and a voice or between a question and a statement or identifying the accented word in a sentence. On several audiovisual tests, an improvement was observed for the sound plus vision condition compared to the vision only condition. This was particularly true for sentence tests, but was not uniform across patients or across tests.

Adult↗
PubMedDate not supplied

Performance of adult Ineraid and Nucleus cochlear implant patients after 3.5 years of use.

Forty-two postlingually deafened adult patients, 21 with a formant extraction version of the Nucleus cochlear implant and 21 with the Ineraid cochlear implant (analog processing), were evaluated on a series of speech perception tests after using their implants for about 3.5 years. A wide range of performance was observed across patients for both devices. All but 4 patients showed an enhancement in their lipreading ability with the implant. Word recognition averaged about 14-19% correct, and word recognition in sentences averaged about 43-49% correct for the two implant groups. Average performance was superior with the Ineraid implant on consonant recognition in noise. An information transmission analysis suggested that vowel perception was influenced by first- and third-formant frequency for the Nucleus, and first-formant and fundamental frequency for the Ineraid patients. It appeared that the Ineraid device was more effective, on average, at conveying information about consonant nasality and frication. For consonant perception, nasality and frication contributed most to the total information transmitted for both implant types. Both devices had difficulty conveying information about vowel second-formant frequency and consonant place information. These scores at 3.5 years are substantially elevated from preoperative performance and, overall, the patients clearly benefit from their implant.

Adult↗