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Bryan E Pfingst

Publications and source records attributed to Bryan E Pfingst.

10 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

Psychophysical metrics and speech recognition in cochlear implant users.

Intersubject variability in perception is a prominent characteristic of people with cochlear implants. This study characterized intersubject differences using simple metrics based on psychophysical measures: maximum comfortable loudness levels (C levels) and dynamic ranges (DRs). In a group of 17 subjects, we assessed across-site variation (ASV) and across-site mean (ASM) values of C levels and DRs for bipolar (BP) and monopolar (MP) stimulation, and examined the relation of these metrics to speech recognition across subjects. Significant negative correlations with speech recognition were found for ASVs of C levels for BP stimulation; i.e., subjects with high ASVs of BP C levels had poor speech recognition. Positive correlations with speech recognition were found for ASMs of C levels and ASMs of DRs for both BP and MP stimulation; i.e., subjects with high mean C levels and large mean DRs had better speech recognition. Thus, these psychophysical metrics are effective for diagnosis of individual differences in performance of subjects with cochlear implants. Furthermore, they point to some potentially useful treatment procedures.

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

Relative contributions of spectral and temporal cues for phoneme recognition.

Cochlear implants provide users with limited spectral and temporal information. In this study, the amount of spectral and temporal information was systematically varied through simulations of cochlear implant processors using a noise-excited vocoder. Spectral information was controlled by varying the number of channels between 1 and 16, and temporal information was controlled by varying the lowpass cutoff frequencies of the envelope extractors from 1 to 512 Hz. Consonants and vowels processed using those conditions were presented to seven normal-hearing native-English-speaking listeners for identification. The results demonstrated that both spectral and temporal cues were important for consonant and vowel recognition with the spectral cues having a greater effect than the temporal cues for the ranges of numbers of channels and lowpass cutoff frequencies tested. The lowpass cutoff for asymptotic performance in consonant and vowel recognition was 16 and 4 Hz, respectively. The number of channels at which performance plateaued for consonants and vowels was 8 and 12, respectively. Within the above-mentioned ranges of lowpass cutoff frequency and number of channels, the temporal and spectral cues showed a tradeoff for phoneme recognition. Information transfer analyses showed different relative contributions of spectral and temporal cues in the perception of various phonetic/acoustic features.

Adult↗
PubMed2005

Efficacy of a cochlear implant simultaneous analog stimulation strategy coupled with a monopolar electrode configuration.

OBJECTIVES: The present study was performed to evaluate the efficacy and clinical feasibility of using monopolar stimulation with the Clarion Simultaneous Analog Stimulation (SAS) strategy in patients with cochlear implants. METHODS: Speech recognition by 10 Clarion cochlear implant users was evaluated by means of 4 different speech processing strategy/electrode configuration combinations; ie, SAS and Continuous Interleaved Sampling (CIS) strategies were each used with monopolar (MP) and bipolar (BP) electrode configurations. The test measures included consonants, vowels, consonant-nucleus-consonant words, and Hearing in Noise Test sentences with a +10 dB signal-to-noise ratio. Additionally, subjective judgments of sound quality were obtained for each strategy/configuration combination. RESULTS: All subjects but 1 demonstrated open-set speech recognition with the SAS/MP combination. The group mean Hearing in Noise Test sentence score for the SAS/MP combination was 31.6% (range, 0% to 92%) correct, as compared to 25.0%, 46.7%, and 37.8% correct for the CIS/BP, CIS/MP, and SAS/BP combinations, respectively. Intersubject variability was high, and there were no significant differences in mean speech recognition scores or mean preference ratings among the 4 strategy/configuration combinations tested. Individually, the best speech recognition performance was with the subject's everyday strategy/configuration combination in 72% of the applicable cases. If the everyday strategy was excluded from the analysis, the subjects performed best with the SAS/MP combination in 37.5% of the remaining cases. CONCLUSIONS: The SAS processing strategy with an MP electrode configuration gave reasonable speech recognition in most subjects, even though subjects had minimal previous experience with this strategy/configuration combination. The SAS/MP combination might be particularly appropriate for patients for whom a full dynamic range of electrical hearing could not be achieved with a BP configuration.

Adult↗
PubMed2004

Across-site threshold variation in cochlear implants: relation to speech recognition.

Functional implications of across-site variation in detection thresholds in subjects with cochlear implants were evaluated by comparing thresholds to speech recognition performance. Detection thresholds for bipolar (BP) and monopolar (MP) stimulation of all available stimulation sites were assessed in 21 subjects with Nucleus CI24M and CI24R(CS) implants. We found significant negative correlations between speech recognition and within-subject across-site threshold variance for both BP and MP stimulation, but no significant correlation of speech recognition with mean threshold levels. These results suggest that across-site variance of detection thresholds could provide a useful early indication of the prognosis for speech recognition and might serve as an indicator for specific therapeutic approaches in individual subjects.

Adult↗
PubMed2003

Across-site variation in detection thresholds and maximum comfortable loudness levels for cochlear implants.

In cochlear implants, variation across stimulation sites in psychophysical detection thresholds (T levels) and maximum comfortable loudness levels (C levels) can be large when narrow-bipolar (BP) stimulation is used. This across-site variation is typically smaller when monopolar (MP) stimulation is used. At least two models can account for across-site variation and the effects of electrode configuration on the magnitude of the variation. According to one model, across-site variation reflects site-to-site differences in the distances between the stimulating electrodes and the sites of action-potential initiation. Under this model, the lower across-site variation with MP stimulation is due to shallower current versus distance gradients. An alternative model assumes that T and C levels depend on integration of activity across the whole population of neurons and that MP stimulation activates neurons over a larger spatial extent than does BP stimulation. If T and C levels are determined by integration of activity across large overlapping populations of neurons, then their values at adjacent sites should be more similar than if these levels result from integration across smaller, more independent populations. We tested the models by examining the effects on across-site variation of three variables believed to affect the spatial extent of activation: electrode configuration, stimulus level within the dynamic range, and electrode-array design. T levels and C levels were measured in 13 subjects with Nucleus CI24M (straight array) and 9 subjects with Nucleus CI24R(CS) (Contour) cochlear implants using bipolar (BP) and monopolar (MP) electrode configurations. Site-to-site variation in T and C levels for BP stimulation was 2.1-3.3 times larger than that for MP stimulation. Contrary to the across-neuron integration hypothesis, no significant differences were found between across-site variation for T levels and that for C levels for the BP configuration. There was considerable overlap in site-to-site variation values for the two types of implants but mean site-to-site variation in C levels for CI24M implants was significantly lower than that for CI24R(CS) implants. Control studies suggested that these results were not an artifact of the scale, and not due to differences in inherent variability of the psychophysical measures, or to the method of quantifying across-site variation.

Adult↗
PubMed2002

Effects of stimulus level on speech perception with cochlear prostheses.

This study is one of a series that examines stimulus features important for cochlear implant function. Here, we examine effects of stimulus level. In subjects with cochlear implants, a number of psychophysical tests of temporal discrimination (pulse rate discrimination, gap detection, etc.) show marked improvement as a function of stimulus level through most or all of the dynamic range, while electrode-place discrimination can improve or degrade as a function of level. In this study, effects of these combined potential influences were studied by examining the effects of stimulus level on syllable identification. We tested two hypotheses: that syllable identification varies as a function of stimulus level and that level and electrode configuration interact in affecting syllable identification. We examined vowel and consonant identification as a function of stimulus level for bipolar and monopolar electrode configurations. We used experimental processor maps where upper and lower stimulation limits of each electrode pair were equated to eliminate confounding effects of dynamic range, which varies across subjects and electrodes. For each channel, stimulation amplitude was set to a fixed percentage of its dynamic range. Eight adult subjects with Nucleus CI24M implants were tested using the SPEAK processing strategy. With each electrode configuration, stimulus levels were tested from 0% to 90% of the dynamic range in nine steps. The effects on consonant and vowel identification were similar. Phoneme identification was usually better for monopolar than for bipolar stimulation. In the lower half of the dynamic range, syllable identification usually increased as a function of stimulus level. In the upper half of the dynamic range, syllable identification continued to increase as a function of level to 90% of the dynamic range for some subjects, while for others there was no appreciable change or a decrease as a function of level. Decreases in performance at high levels were more common with monopolar than bipolar stimulation. These results suggest that if speech processors are programmed to optimize level for each individual, speech perception performance could be improved.

Acoustic Stimulation↗
PubMed2002

Features of stimulation affecting tonal-speech perception: implications for cochlear prostheses.

Tone languages differ from English in that the pitch pattern of a single-syllable word conveys lexical meaning. In the present study, dependence of tonal-speech perception on features of the stimulation was examined using an acoustic simulation of a CIS-type speech-processing strategy for cochlear prostheses. Contributions of spectral features of the speech signals were assessed by varying the number of filter bands, while contributions of temporal envelope features were assessed by varying the low-pass cutoff frequency used for extracting the amplitude envelopes. Ten normal-hearing native Mandarin Chinese speakers were tested. When the low-pass cutoff frequency was fixed at 512 Hz, consonant, vowel, and sentence recognition improved as a function of the number of channels and reached plateau at 4 to 6 channels. Subjective judgments of sound quality continued to improve as the number of channels increased to 12, the highest number tested. Tone recognition, i.e., recognition of the four Mandarin tone patterns, depended on both the number of channels and the low-pass cutoff frequency. The trade-off between the temporal and spectral cues for tone recognition indicates that temporal cues can compensate for diminished spectral cues for tone recognition and vice versa. An additional tone recognition experiment using syllables of equal duration showed a marked decrease in performance, indicating that duration cues contribute to tone recognition. A third experiment showed that recognition of processed FM patterns that mimic Mandarin tone patterns was poor when temporal envelope and duration cues were removed.

Acoustic Stimulation↗