Biomedical subjects

Margaret W Skinner

Publications and source records attributed to Margaret W Skinner.

13 recordsLinked to original sources

PubMed2006

Audibility and speech perception of children using wide dynamic range compression hearing AIDS.

PURPOSE: This study examined the relation of audibility for frequency-specific sounds and the Speech Intelligibility Index (SII) to speech perception abilities of children with sensorineural hearing loss using digital signal-processing hearing aids with wide dynamic range compression. METHOD: Twenty-six children age 5-15 years with pure-tone averages (0.5, 1.0, and 2.0 kHz) from 60-98 dB HL participated. Three subgroups were created based on the compression characteristics of each hearing aid. Minimum audibility was determined using aided thresholds for frequency-modulated tones and the SII calculated at 55 and 70 dB SPL using the simulated real-ear output of the hearing aid. The Lexical Neighborhood Test (LNT; K. I. Kirk, D. B. Pisoni, & M. J. Osberger, 1995) was presented at 50 and 70 dB SPL. RESULTS: LNT scores at 70 dB SPL were significantly higher than at 50 dB SPL. Average aided thresholds at 0.5, 1.0, and 2.0 kHz were negatively correlated with LNT scores at 50 dB SPL, and SIIs at 55 and 70 dB SPL were positively correlated with LNT scores at 50 and 70 dB SPL. CONCLUSIONS: Results support using aided thresholds and speech test scores at soft to loud levels as part of the amplification fitting process.

Auditory Threshold↗

PubMed2006

Evaluation of equivalency in two recordings of monosyllabic words.

Thirty "new" lists of monosyllabic words were created at the University of Melbourne and recorded by Australian and American English speakers. These new lists and the ten original CNC lists (Peterson and Lehiste, 1962) were used during the feasibility study of the Nucleus Research Platform 8 Cochlear Implant System (Holden et al, 2004). Performance was similar across original and new lists for six implanted Australian subjects; for four implanted U.S. subjects, mean performance was 23 percentage points lower with the new than with the original lists. To evaluate differences between original and new lists for the American English recording, 22 CI recipients were administered all 40 CNC lists (30 new and 10 original lists). The overall mean word score for the new lists was significantly lower (22.3 percentage points) than for the original lists. Acoustic analysis revealed that decreased performance was most likely due to reduced amplitudes of certain initial and final consonants. The new CNC lists can be used as more difficult test material for clinical research.

Acoustic Stimulation↗

PubMed2005

Speech recognition with the advanced combination encoder and transient emphasis spectral maxima strategies in nucleus 24 recipients.

One of the difficulties faced by cochlear implant (CI) recipients is perception of low-intensity speech cues. A. E. Vandali (2001) has developed the transient emphasis spectral maxima (TESM) strategy to amplify short-duration, low-level sounds. The aim of the present study was to determine whether speech scores would be significantly higher with TESM than with the advanced combination encoder (ACE) strategy fitted using procedures that optimize perception of soft speech and other sounds. Eight adult recipients of the Nucleus 24 CI system participated in this study. No significant differences in scores were seen between ACE and TESM for consonant-vowel nucleus-consonant (CNC) words presented at 55 and 65 dB SPL, for sentences in noise presented at 65 dB SPL at 2 different signal-to-noise ratios, or for closed-set vowels and consonants presented at 60 dB SPL. However, perception of stop consonants within CNC words presented at the lower level (55 dB SPL) was significantly higher with TESM than ACE. In addition, percentage of information transmitted for words at 55 dB SPL was significantly higher with TESM than with ACE for manner and voicing features for consonants in the initial word position. Analysis of closed-set consonants presented at 60 dB SPL revealed percentage of information transmitted for manner was significantly higher with TESM than with ACE. These improvements with TESM were small compared with those reported by Vandali for recipients of the Nucleus 22 CI system. It appears that mapping techniques used to program speech processors and improved processing capabilities of the Nucleus 24 system contributed to soft sounds being understood almost as well with ACE as with TESM. However, half of the participants preferred TESM to ACE for use in everyday life, and all but 1 used TESM in specific listening situations. Clinically, TESM may be useful to ensure the audibility of low-intensity, short-duration acoustic cues that are important for understanding speech, for recipients who are difficult to map, or if insufficient time precludes the use of mapping techniques to increase audibility of soft sound.

Adult↗

PubMed2004

Recognition of speech presented at soft to loud levels by adult cochlear implant recipients of three cochlear implant systems.

OBJECTIVE: The purpose of this study was to conduct a large-scale investigation with adult recipients of the Clarion, Med-El, and Nucleus cochlear implant systems to (1) determine average scores and ranges of performance for word and sentence stimuli presented at three intensity levels (70, 60, and 50 dB SPL); (2) provide information on the variability of scores for each subject by obtaining test-retest measures for all test conditions; and (3) further evaluate the potential use of lower speech presentation levels (i.e., 60 and/or 50 dB SPL) in cochlear implant candidacy assessment. DESIGN: Seventy-eight adult cochlear implant recipients, 26 with each of the three cochlear implant systems, participated in the study. To ensure that the data collected reflect the range of performance of adult recipients using recent technology for the three implant systems (Clarion HiFocus I or II, Med-El Combi 40+, Nucleus 24M or 24R), a composite range and distribution of consonant-nucleus-consonant (CNC) monosyllabic word scores was determined. Subjects using each device were selected to closely represent this range and distribution of CNC performance. During test sessions, subjects were administered the Hearing in Noise Test (HINT) sentence test and the CNC word test at three presentation levels (70, 60, and 50 dB SPL). HINT sentences also were administered at 60 dB SPL with a signal-to-noise ratio (SNR) of +8 dB. Warble tones were used to determine sound-field threshold levels from 250 to 4000 Hz. Test-retest measures were obtained for each of the speech recognition tests as well as for warble-tone sound-field thresholds. RESULTS: Cochlear implant recipients using the Clarion, Med-El, or Nucleus devices performed on average equally as well at 60 compared with 70 dB SPL when listening for words and sentences. Additionally, subjects had substantial open-set speech perception performance at the softer level of 50 dB SPL for the same stimuli; however, subjects' ability to understand speech was poorer when listening in noise to signals of greater intensity (60 dB SPL + 8 SNR) than when listening to signals presented at a soft presentation level (50 dB SPL) in quiet. A significant correlation was found between sound-field thresholds and speech recognition scores for presentation levels below 70 dB SPL. The results demonstrated a high test-retest reliability with cochlear implant users for these presentation levels and stimuli. Average sound-field thresholds were between 24 and 29 dB HL for frequencies of 250 to 4000 Hz, and results across sessions were essentially the same. CONCLUSIONS: Speech perception measures used with cochlear implant candidates and recipients should reflect the listening challenges that individuals encounter in natural communication situations. These data provide the basis for recommending new candidacy criteria based on speech recognition tests presented at 60 and/or 50 dB SPL, intensity levels that reflect real-life listening, rather than 70 dB SPL.

Adult↗

PubMed2004

Effect of frequency boundary assignment on vowel recognition with the Nucleus 24 ACE speech coding strategy.

Two speech processor programs (MAPs) differing only in electrode frequency boundary assignments were created for each of eight Nucleus 24 Cochlear Implant recipients. The default MAPs used typical frequency boundaries, and the experimental MAPs reassigned one additional electrode to vowel formant regions. Four objective speech tests and a questionnaire were used to evaluate speech recognition with the two MAPs. Results for the closed-set vowel test and the formant discrimination test showed small but significant improvement in scores with the experimental MAP. Differences for the Consonant-Vowel Nucleus-Consonant word test and closed-set consonant test were nonsignificant. Feature analysis revealed no significant differences in information transmission. Seven of the eight subjects preferred the experimental MAP, reporting louder, crisper, and clearer sound. The results suggest that Nucleus 24 recipients should be given an opportunity to compare a MAP that assigns more electrodes in vowel formant regions with the default MAP to determine which provides the most benefit in everyday life.

Adult↗

PubMed2003

An investigation of input level range for the nucleus 24 cochlear implant system: speech perception performance, program preference, and loudness comfort ratings.

OBJECTIVE: Cochlear implant recipients often have limited access to lower level speech sounds. In this study we evaluated the effects of varying the input range characteristics of the Nucleus 24 cochlear implant system on recognition of vowels, consonants, and sentences in noise and on listening in everyday life. DESIGN: Twelve subjects participated in the study that was divided into two parts. In Part 1 subjects used speech processor (Nucleus 24 SPrint trade mark ) programs adjusted for three input sensitivity settings: a standard or default microphone sensitivity setting (MS 8), a setting that increased the input sensitivity by 10.5 dB (MS 15), and the same setting that increased input sensitivity but also incorporated the automatic sensitivity control (ASC; i.e., MS 15A) that is designed to reduce the loudness of noise. The default instantaneous input dynamic range (IIDR) of 30 dB was used in these programs (i.e., base level of 4; BL 4). Subjects were tested using each sensitivity program with vowels and consonants presented at very low to casual conversational levels of 40 dB SPL and 55 dB SPL, respectively. They were also tested with sentences presented at a raised level of 65 dB SPL in multi-talker babble at individually determined signal to noise ratios. In addition, subjects were given experience outside of the laboratory for several weeks. They were asked to complete a questionnaire where they compared the programs in different listening situations as well as the loudness of environmental sounds, and state the setting they preferred overall. In Part 2 of the study, subjects used two programs. The first program was their preferred sensitivity program from Part 1 that had an IIDR of 30 dB (BL 4). Seven subjects used MS 8 and four used MS 15, and one used the noise reduction program MS 15A. The second program used the same microphone sensitivity but had the IIDR extended by an additional 8 to 10 dB (BL 1/0). These two programs were evaluated similarly in the speech laboratory and with take-home experience as in Part 1. RESULTS PART 1: Increasing the microphone input sensitivity by 10.5 dB (from MS 8 to MS 15) significantly improved the perception of vowels and consonants at 40 and 55 dB SPL. The group mean improvement in vowel scores was 25 percentage points at 40 dB SPL and 4 percentage points at 55 dB SPL. The group mean improvement for consonants was 23 percentage points at 40 dB SPL and 11 percentage points at 55 dB SPL. Increased input sensitivity did not significantly reduce the perception of sentences presented at 65 dB SPL in babble despite the fact that speech peaks were then within the compressed range above the SPrint processor's automatic gain control (AGC) knee-point. Although there was a demonstrable advantage for perception of low-level speech with the higher input sensitivity (MS 15 and 15A), seven of the 12 subjects preferred MS 8, four preferred MS 15 or 15A, and one had no preference overall. Approximately half the subjects preferred MS 8 across the 18 listening situations, whereas an average of two subjects preferred MS 15 or 15A. The increased microphone sensitivity of MS 15 substantially increased the loudness of environmental sounds. However, use of the ASC noise reduction setting with MS 15 reduced the loudness of environmental sounds to equal or below that for MS 8. RESULTS PART 2: The increased instantaneous input range gave some improvement (8 to 9 percentage points for the 40 dB SPL presentation level) in the perception of consonants. There was no statistically significant increase in vowel scores. Mean scores for sentences presented at 65 dB SPL in babble were significantly lower (5 percentage points) for the increased IIDR setting. Subjects had no preference for the increased IIDR over the default. The IIDR setting had no effect on the loudness of environmental sounds. CONCLUSIONS: Given the fact that individuals differ in threshold (T) and comfort (C) levels for electrical stimulation, and preferred microphone sensitivity, volume control, and noise-reduction settings, it is essential for the clinicid recipient to determine what combination is best for the individual over several sessions. The results of this study clearly show the advantage of using higher microphone sensitivity settings than the default MS 8 to provide better speech recognition for low-level stimuli. However, it was also necessary to adjust other parameters such as map C levels, automatic sensitivity control and base level, to optimize loudness comfort in the diversity of listening situations an individual encounters in everyday life.

Auditory Threshold↗

PubMed2003

Blind deblurring of spiral CT images.

To discriminate fine anatomical features in the inner ear, it has been desirable that spiral computed tomography (CT) may perform beyond their current resolution limits with the aid of digital image processing techniques. In this paper, we develop a blind deblurring approach to enhance image resolution retrospectively without complete knowledge of the underlying point spread function (PSF). An oblique CT image can be approximated as the convolution of an isotropic Gaussian PSF and the actual cross section. Practically, the parameter of the PSF is often unavailable. Hence, estimation of the parameter for the underlying PSF is crucially important for blind image deblurring. Based on the iterative deblurring theory, we formulate an edge-to-noise ratio (ENR) to characterize the image quality change due to deblurring. Our blind deblurring algorithm estimates the parameter of the PSF by maximizing the ENR, and deblurs images. In the phantom studies, the blind deblurring algorithm reduces image blurring by about 24%, according to our blurring residual measure. Also, the blind deblurring algorithm works well in patient studies. After fully automatic blind deblurring, the conspicuity of the submillimeter features of the cochlea is substantially improved.

Algorithms↗

PubMed2003

Optimizing cochlear implant speech performance.

Results of studies performed in our laboratory suggest that cochlear implant recipients understand speech best if the following speech processor parameters are individually chosen for each person: minimum and maximum stimulation levels on each electrode in the speech processor program (MAP), stimulation rate, and speech coding strategy. If these and related parameters are chosen to make soft sounds (from approximately 100 to 6,000 Hz) audible at as close to 20 dB hearing level as possible and loud sounds not too loud, recipients have the opportunity to hear speech in everyday life situations that are of key importance to children who are learning language and to all recipients in terms of ease of communication.

Auditory Threshold↗

PubMed2002

CT-derived estimation of cochlear morphology and electrode array position in relation to word recognition in Nucleus-22 recipients.

This study extended the findings of Ketten et al. [Ann. Otol. Rhinol. Laryngol. Suppl. 175:1-16 (1998)] by estimating the three-dimensional (3D) cochlear lengths, electrode array intracochlear insertion depths, and characteristic frequency ranges for 13 more Nucleus-22 implant recipients based on in vivo computed tomography (CT) scans. Array insertion depths were correlated with NU-6 word scores (obtained one year after SPEAK strategy use) by these patients and the 13 who used the SPEAK strategy from the Ketten et al. study. For these 26 patients, the range of cochlear lengths was 29.1-37.4 mm. Array insertion depth range was 11.9-25.9 mm, and array insertion depth estimated from the surgeon's report was 1.14 mm longer than CT-based estimates. Given the assumption that the human hearing range is fixed (20-20,000 Hz) regardless of cochlear length, characteristic frequencies at the most apical electrode (estimated with Greenwood's equation [Greenwood DD (1990) A cochlear frequency--position function of several species--29 years later. J Acoust. Soc. Am. 33: 1344-1356] and a patient-specific constant as) ranged from 308 to 3674 Hz. Patients' NU-6 word scores were significantly correlated with insertion depth as a percentage of total cochlear length (R = 0.452; r2 = 0.204; p = 0.020), suggesting that part of the variability in word recognition across implant recipients can be accounted for by the position of the electrode array in the cochlea. However, NU-6 scores ranged from 4% to 81% correct for patients with array insertion depths between 47% and 68% of total cochlear length. Lower scores appeared related to low spiral ganglion cell survival (e.g., lues), aberrant current paths that produced facial nerve stimulation by apical electrodes (i.e., otosclerosis), central auditory processing difficulty, below-average verbal abilities, and early Alzheimer's disease. Higher scores appeared related to patients' high-average to above-average verbal abilities. Because most patients' scores increased with SPEAK use, it is hypothesized that they accommodated to the shift in frequency of incoming sound to a higher pitch percept with the implant than would normally be perceived acoustically.

Adult↗

PubMed2002

Nucleus 24 advanced encoder conversion study: performance versus preference.

OBJECTIVE: The Nucleus 24 Advanced Encoder Conversion Study was designed to determine the safety and effectiveness of the advanced combination encoder (ACE) and continuous interleaved sampling (CIS) speech coding strategies compared with that of the spectral peak (SPEAK) strategy in a large sample of postlinguistically deaf adults. Data from this study were analyzed to test the hypothesis that the group of subjects who prefer a given strategy for use in everyday life obtain significantly higher speech recognition scores (as a group) with the preferred strategy than with nonpreferred ones. DESIGN: The first 100 adults implanted with the Nucleus 24 Cochlear Implant System who had a minimum of 3 mo experience with the device were invited to participate. Those who accepted were randomly assigned to one of two groups for an initial 6-wk use of either the ACE or the CIS strategy; the other strategy was used during the second 6-wk period. Parameters in subjects' SPrint speech processor programs were adjusted to maximize perceived benefit with each strategy in everyday life. Recognition of medial consonants and vowels, CNC words, CUNY sentences in quiet and at + 10 dB signal to noise ratio, and HINT sentences in quiet was initially evaluated at the beginning of the study with the SPEAK strategy and at the end of the two 6-wk periods with the ACE and CIS strategies. Then subjects' processors were programmed with all three strategies for use in everyday life. After 3-wk use, a final evaluation of speech recognition with the HINT sentences in quiet and CUNY sentences at +10 dB signal to noise ratio was performed with each strategy. Subjects also responded to a questionnaire giving their strategy preference for most listening situations, the percentage of time they used each strategy, and the strategy they found gave them the best hearing and understanding of speech in 19 listening situations. RESULTS: Of the 62 subjects who participated, 56 subjects reported that they preferred one strategy for most listening situations (ACE strategy: 37 [59.7%]; SPEAK strategy: 14 [22.6%]; CIS strategy: 5 [8.0%]) and six subjects did not prefer a single strategy (9.7%). For the group who preferred one strategy, the preferred strategy resulted in higher scores than for one of the other strategies at the initial evaluation on CUNY sentences in quiet and noise and at the final evaluation on HINT sentences in quiet and CUNY sentences in noise for approximately two-thirds of the subjects. Strategy preference and performance were not significantly related for the remaining dependent measures. There also was strong agreement between the preferred strategy, percentage time this strategy was used, and the number of specific listening situations the preferred strategy was chosen for best hearing and understanding of speech. Although the majority of subjects strongly preferred a single strategy, some preferred to use two or three strategies, and a few were not sure which strategy they preferred for the majority of listening situations. Of the 19 subjects who reported that it was useful to use different strategies for different listening situations, only 5 of the 13 subjects, who responded to a follow-up questionnaire sent 18 mo later, continued to use multiple strategies. CONCLUSIONS: There was a significant relation between subjects' strategy preference based on experience in everyday life and their performance on the sentence tests, particularly sentences in noise. Important individual differences in strategy preference as well as in rate and number of channels stimulated per cycle within the ACE and CIS strategies emerged during the study. At the end of this process, over half of the subjects preferred the ACE strategy, and over double the number preferred the SPEAK strategy compared with the CIS strategy. To provide newly implanted recipients with as much benefit as possible, it is important that the speech processor program with each strategy be adjusted to maximize perceived benefit sequentially and then the three strategies need to be compared. With the four memories of the SPrint processor and a recipient who adapts quickly to hearing sound with different speech coding strategies, it may be possible to accomplish this comparison clinically through weekly fitting sessions plus listening in everyday life over a period of approximately 6 wk. At the end of this fitting process, most recipients probably will prefer to use one strategy, whereas some may prefer two or all three strategies to maximize their ability to hear in different listening situations.

Acoustic Stimulation↗

PubMed2002

Speech recognition with the nucleus 24 SPEAK, ACE, and CIS speech coding strategies in newly implanted adults.

OBJECTIVE: The objective of this study was to determine whether 1) the SPEAK, ACE or CIS speech coding strategy was associated with significantly better speech recognition for individual subjects implanted with the Nucleus CI24M internal device who used the SPrint speech processor, and 2) whether a subject's preferred strategy for use in everyday life provided the best speech recognition. DESIGN: Twelve postlinguistically deaf, newly implanted adults participated. Initial preference for the three strategies was obtained with paired-comparison testing on the first day of implant stimulation with seven of eight U.S. subjects. During the first 12 wk, all subjects used each strategy alone for 4 wk to give them experience with the strategy and to identify preferred speech processor program parameters and settings that would be used in subsequent testing. For the next 6 wk, subjects used one strategy at a time for 2-wk intervals in the same order they had for the first 12 wk. At the end of each 2-wk interval, speech recognition testing was conducted with all three strategies. At the end of the 6 wk, all three strategies were placed on each subject's processor, and subjects were asked to compare listening with these three programs in as many situations as possible for the next 2 wk. When they returned, subjects responded to a questionnaire asking about their preferred strategy and responded to two lists of medial consonants using each of the three strategies. The U.S. subjects also responded to two lists of medial vowels with the three strategies. RESULTS: Six of the 12 subjects in the present study had significantly higher CUNY sentence scores with the ACE strategy than with one or both of the other strategies; one of the 12 subjects had a significantly higher score with SPEAK than with ACE. In contrast, only two subjects had significantly higher CNC word and phoneme scores with one or two strategies than with the third strategy. One subject had a significantly higher vowel score with the SPEAK strategy than with the CIS strategy; and no subjects had significantly higher consonant scores with any strategy. Seven of 12 subjects preferred the ACE strategy, three preferred the SPEAK strategy, and two preferred the CIS strategy. Subjects' responses on a questionnaire agreed closely with strategy preference from comparisons made in everyday life. There was a strong relation between the preferred strategy and scores on CUNY sentences but not for the other speech tests. For all subjects, except one, the preferred strategy was the one with the highest CUNY sentence score or was a strategy with a CUNY score not significantly lower than the highest score. CONCLUSIONS: Despite differences in research design, there was remarkably close agreement in the pattern of group mean scores for the three strategies for CNC words and CUNY sentences in noise between the present study and the Conversion study (Arndt, Staller, Arcaroli, Hines, & Ebinger, Reference Note 1). In addition, essentially the same percentage of subjects preferred each strategy. For both studies, the strategy with which subjects had the highest score on the CUNY sentences in noise evaluation was strongly related to the preferred strategy; this relation was not strong for CNC words, CNC phonemes, vowels or consonants (Skinner, Arndt, & Staller, 2002). These results must be considered within the following context. For each strategy, programming parameters preferred for use in everyday life were determined before speech recognition was evaluated. In addition, implant recipients had experience listening with all three strategies in many situations in everyday life before choosing a preferred strategy. Finally, 11 of the 12 subjects strongly preferred one of the three strategies. Given the results and research design, it is recommended that clinicians fit each strategy sequentially starting with the ACE strategy so that the preferred programming parameters are determined for each strategy before recipients compare pairs of strategies. The goal is to provide the best opportunity for individuals to hear in everyday life within a clinically acceptable time period (e.g., 6 wk).

Acoustic Stimulation↗

PubMed2002

Effects of stimulation rate with the Nucleus 24 ACE speech coding strategy.

OBJECTIVE: The primary objective of the study was to determine whether individual cochlear implant recipients recognize speech better with an electrical stimulation rate of 720 or 1800 pulses per second per channel (pps/ch) using the Nucleus 24 Advanced Combination Encoder (ACE) speech coding strategy. The secondary objective was to determine, for each active electrode, the relation between psychophysical measures and MAP minimum and maximum stimulation levels for each rate, as well as the stability of MAP minimum and maximum levels during the study. DESIGN: Eight postlinguistically deaf adults implanted with the Nucleus 24 device participated in this study comparing the effect of a moderate (720 pps/ch) and a fast (1800 pps/ch) rate of electrical stimulation on speech recognition of words in quiet and sentences in noise presented at 50, 60, and 70 dB SPL in the laboratory and on listening to sound in everyday life over a 14-wk time period. At the beginning of the study, psychophysical measures (i.e., counted threshold and maximum acceptable loudness [MAL] levels) were obtained for each active electrode with each of the two rates to initially set MAP minimum and maximum stimulation levels. These levels were then adjusted to make speech and environmental sound clear and comfortable in everyday life. Threshold and MAL levels were obtained again half way through the study to monitor possible hearing changes. A four-phase test design for evaluation of speech recognition was followed; an equal number of subjects started with each of the two rates and alternated rates for each phase. In the last 2 wk of each phase, word and sentence scores were obtained, and subjects responded to a questionnaire. For the group, factorial analyses of variance were conducted for subject, stimulation rate, and time period (first two phases versus second two phases) for words, phonemes within words, and sentences at each level. Additional analyses were obtained for individual subjects. RESULTS: Group mean scores across time periods were significantly higher for 1800 pps/ch than 720 pps/ch for phonemes and sentences in noise at 50 dB SPL. There was no significant difference in scores for phonemes and sentences at 60 and 70 dB SPL or for words at any of the three levels. Group mean scores across stimulation rate were significantly higher during the second half than the first half of the study for words, phonemes, and sentences at 50 dB SPL. This result is consistent with subjects learning to recognize speech cues near threshold. A subject by rate interaction was seen for sentences at 70 dB SPL and for all three speech measures at 50 dB SPL. These interactions reflect the fact that two subjects performed significantly better with 720 pps/ch, whereas two other subjects performed significantly better with 1800 pps/ch. Responses to the questionnaire indicated that two subjects preferred 720 pps/ch, three preferred 1800 pps/ch, and three had no preference. The minimum and/or maximum levels in most subjects' final MAPs differed from the psychophysical measures for both rates. Changes in Current Level at threshold and MAL were minimal from the first to the second half of the study for each rate. CONCLUSIONS: More than half the subjects preferred one of the two rates for use in everyday life, and four subjects performed significantly better with one of the two rates on at least one test measure. These findings underscore the clinical importance of creating MAPs for each implant recipient that include at least a moderate and a fast rate within ACE during the first months of device use. Given the significant learning effects for soft speech that occurred over several weeks use of each rate in this study, it is suggested that each rate be used alone for a week or two before comparing them and deciding which provides more benefit. In addition, adjustments in an individual's MAP minimum and maximum levels are needed at each rate so soft and normal conversational speech as well as loud sound are clear and comfortable in everyday life.

Adult↗

PubMed2002

Blind deblurring of spiral CT images-comparative studies on edge-to-noise ratios.

A recently developed blind deblurring algorithm based on the edge-to-noise ratio has been applied to improve the quality of spiral CT images. Since the discrepancy measure used to quantify the edge and noise effects is not symmetric, there are several ways to formulate the edge-to-noise ratio. This article is to investigate the performance of those ratios with phantom and patient data. In the phantom study, it is shown that all the ratios share similar properties, validating the blind deblurring algorithm. The image fidelity improvement varies from 29% to 33% for different ratios, according to the root mean square error (RMSE) criterion; the optimal iteration number determined for each ratio varies from 25 to 35. Those ratios that are associated with most satisfactory performance are singled out for the image fidelity improvement of about 33% in the numerical simulation. After automatic blind deblurring with the selected ratios, the spatial resolution of CT is substantially refined in all the cases tested.

Algorithms↗