Optimizations for the Electrically-Evoked Stapedial Reflex Threshold Measurement in Cochlear Implant Recipients.

OBJECTIVE: The electrically-evoked stapedial reflex threshold (eSRT) has proven to be useful in setting upper stimulation levels of cochlear implant recipients. However, the literature suggests that the reflex can be difficult to observe in a significant percentage of the population. The primary goal of this investigation was to assess the difference in eSRT levels obtained with alternative acoustic admittance probe tone frequencies. DESIGN: A repeated-measures design was used to examine the effect of 3 probe tone frequencies (226, 678, and 1000 Hz) on eSRT in 23 adults with cochlear implants. RESULTS: The mean eSRT measured using the conventional probe tone of 226 Hz was significantly higher than the mean eSRT measured with use of 678 and 1000 Hz probe tones. The mean eSRT were 174, 167, and 165 charge units with use of 226, 678, and 1000 Hz probe tones, respectively. There was not a statistically significant difference between the average eSRTs for probe tones 678 and 1000 Hz. Twenty of 23 participants had eSRT at lower charge unit levels with use of either a 678 or 1000 Hz probe tone when compared with the 226 Hz probe tone. Two participants had eSRT measured with 678 or 1000 Hz probe tones that were equal in level to the eSRT measured with a 226 Hz probe tone. Only 1 participant had an eSRT that was obtained at a lower charge unit level with a 226 Hz probe tone relative to the eSRT obtained with a 678 and 1000 Hz probe tone. CONCLUSIONS: The results of this investigation demonstrate that the use of a standard 226 Hz probe tone is not ideal for measurement of the eSRT. The use of higher probe tone frequencies (i.e., 678 or 1000 Hz) resulted in lower eSRT levels when compared with the eSRT levels obtained with use of a 226 probe tone. In addition, 4 of the 23 participants included in this study did not have a measureable eSRT with use of a 226 Hz probe tone, but all of the participants had measureable eSRT with use of both the 678 and 1000 Hz probe tones. Additional work is required to understand the clinical implication of these changes in the context of cochlear implant programming.

Development and validation of the pediatric AzBio sentence lists.

OBJECTIVES: The goal of this study was to create and validate a new set of sentence lists that could be used to evaluate the speech-perception abilities of listeners with hearing loss in cases where adult materials are inappropriate due to difficulty level or content. The authors aimed to generate a large number of sentence lists with an equivalent level of difficulty for the evaluation of performance over time and across conditions. DESIGN: The original Pediatric AzBio sentence corpus included 450 sentences recorded from one female talker. All sentences included in the corpus were successfully repeated by kindergarten and first-grade students with normal hearing. The mean intelligibility of each sentence was estimated by processing each sentence through a cochlear implant simulation and calculating the mean percent correct score achieved by 15 normal-hearing listeners. After sorting sentences by mean percent correct scores, 320 sentences were assigned to 16 lists of equivalent difficulty. List equivalency was then validated by presenting all sentence lists, in a novel random order, to adults and children with hearing loss. A final-validation stage examined single-list comparisons from adult and pediatric listeners tested in research or clinical settings. RESULTS: The results of the simulation study allowed for the creation of 16 lists of 20 sentences. The average intelligibility of each list ranged from 78.4 to 78.7%. List equivalency was then validated, when the results of 16 adult cochlear implant users and 9 pediatric hearing aid and cochlear implant users revealed no significant differences across lists. The binomial distribution model was used to account for the inherent variability observed in the lists. This model was also used to generate 95% confidence intervals for one and two list comparisons. A retrospective analysis of 361 instances from 78 adult cochlear implant users and 48 instances from 36 pediatric cochlear implant users revealed that the 95% confidence intervals derived from the model captured 94% of all responses (385 of 409). CONCLUSIONS: The cochlear implant simulation was shown to be an effective method for estimating the intelligibility of individual sentences for use in the evaluation of cochlear implant users. Furthermore, the method used for constructing equivalent sentence lists and estimating the inherent variability of the materials has also been validated. Thus, the AzBio Pediatric Sentence Lists are equivalent and appropriate for the assessment of speech-understanding abilities of children with hearing loss as well as adults for whom performance on AzBio sentences is near the floor.

Clinical assessment of spectral modulation detection for adult cochlear implant recipients: a non-language based measure of performance outcomes.

OBJECTIVE: Spectral modulation detection (SMD) provides a psychoacoustic estimate of spectral resolution. The SMD threshold for an implanted ear is highly correlated with speech understanding and is thus a non-linguistic, psychoacoustic index of speech understanding. This measure, however, is time and equipment intensive and thus not practical for clinical use. Thus the purpose of the current study was to investigate the efficacy of a quick SMD task with the following three study aims: (1) to investigate the correlation between the long psychoacoustic, and quick SMD tasks, (2) to determine the test/retest variability of the quick SMD task, and (3) to evaluate the relationship between the quick SMD task and speech understanding. DESIGN: This study included a within-subjects, repeated-measures design. STUDY SAMPLE: Seventy-six adult cochlear implant recipients participated. RESULTS: The results were as follows: (1) there was a significant correlation between the long psychoacoustic, and quick SMD tasks, (2) the test-retest variability of the quick SMD task was highly significant and, (3) there was a significant positive correlation between the quick SMD task and monosyllabic word recognition. CONCLUSIONS: The results of this study represent the direct clinical translation of a research-proven task of SMD into a quick, clinically feasible format.

Relationship between auditory function of nonimplanted ears and bimodal benefit.

OBJECTIVES: Patients with a cochlear implant (CI) in one ear and a hearing aid in the other ear commonly achieve the highest speech-understanding scores when they have access to both electrically and acoustically stimulated information. At issue in this study was whether a measure of auditory function in the hearing aided ear would predict the benefit to speech understanding when the information from the aided ear was added to the information from the CI. DESIGN: The subjects were 22 bimodal listeners with a CI in one ear and low-frequency acoustic hearing in the nonimplanted ear. The subjects were divided into two groups-one with mild-to-moderate low-frequency loss and one with severe-to-profound loss. Measures of auditory function included (1) audiometric thresholds at 750 Hz or lower, (2) speech-understanding scores (words in quiet and sentences in noise), and (3) spectral-modulation detection (SMD) thresholds. In the SMD task, one stimulus was a flat spectrum noise and the other was a noise with sinusoidal modulations at 1.0 peak/octave. RESULTS: Significant correlations were found among all three measures of auditory function and the benefit to speech understanding when the acoustic and electric stimulation were combined. Benefit was significantly correlated with audiometric thresholds (r = -0.814), acoustic speech understanding (r = 0.635), and SMD thresholds (r = -0.895) in the hearing aided ear. However, only the SMD threshold was significantly correlated with benefit within the group with mild-to-moderate loss (r = -0.828) and within the group with severe-to-profound loss (r = -0.896). CONCLUSIONS: The SMD threshold at 1 cycle/octave has the potential to provide clinicians with information relevant to the question of whether an ear with low-frequency hearing is likely to add to the intelligibility of speech provided by a CI.

Localization and speech understanding by a patient with bilateral cochlear implants and bilateral hearing preservation.

OBJECTIVES: The authors describe the localization and speech-understanding abilities of a patient fit with bilateral cochlear implants (CIs) for whom acoustic low-frequency hearing was preserved in both cochleae. DESIGN: Three signals were used in the localization experiments: low-pass, high-pass, and wideband noise. Speech understanding was assessed with the AzBio sentences presented in noise. RESULTS: Localization accuracy was best in the aided, bilateral acoustic hearing condition, and was poorer in both the bilateral CI condition and when the bilateral CIs were used in addition to bilateral low-frequency hearing. Speech understanding was best when low-frequency acoustic hearing was combined with at least one CI. CONCLUSIONS: The authors found that (1) for sound source localization in patients with bilateral CIs and bilateral hearing preservation, interaural level difference cues may dominate interaural time difference cues and (2) hearing-preservation surgery can be of benefit to patients fit with bilateral CIs.

Auditory training in patients with unilateral cochlear implant and contralateral acoustic stimulation.

OBJECTIVES: It was hypothesized that auditory training would allow bimodal patients to combine in a better manner the low-frequency acoustic information provided by a hearing aid with the electric information provided by a cochlear implant, thus maximizing the benefit of combining acoustic (A) and electric (E) stimulation (EAS). DESIGN: Performance in quiet or in the presence of a multitalker babble at +5 dB signal to noise ratio was evaluated in seven bimodal patients before and after auditory training. The performance measures comprised identification of vowels and consonants, consonant-nucleus-consonant words, sentences, voice gender, and emotion. Baseline performance was evaluated in the A-alone, E-alone, and combined EAS conditions once per week for 3 weeks. A phonetic-contrast training protocol was used to facilitate speech perceptual learning. Patients trained at home 1 hour a day, 5 days a week, for 4 weeks with both their cochlear implant and hearing aid devices on. Performance was remeasured after the 4 weeks of training and 1 month after training stopped. RESULTS: After training, there was significant improvement in vowel, consonant, and consonant-nucleus-consonant word identification in the E and EAS conditions. The magnitude of improvement in the E condition was equivalent to that in the EAS condition. The improved performance was largely retained 1 month after training stopped. CONCLUSION: Auditory training, in the form administered in this study, can improve bimodal patients' overall speech understanding by improving E-alone performance.

Development and validation of the AzBio sentence lists.

OBJECTIVES: The goal of this study was to create and validate a new set of sentence lists that could be used to evaluate the speech perception abilities of hearing-impaired listeners and cochlear implant (CI) users. Our intention was to generate a large number of sentence lists with an equivalent level of difficulty for the evaluation of performance over time and across conditions. DESIGN: The AzBio sentence corpus includes 1000 sentences recorded from two female and two male talkers. The mean intelligibility of each sentence was estimated by processing each sentence through a five-channel CI simulation and calculating the mean percent correct score achieved by 15 normal-hearing listeners. Sentences from each talker were sorted by percent correct score, and 165 sentences were selected from each talker and were then sequentially assigned to 33 lists, each containing 20 sentences (5 sentences from each talker). List equivalency was validated by presenting all lists, in random order, to 15 CI users. RESULTS: Using sentence scores from the CI simulation study produced 33 lists of sentences with a mean score of 85% correct. The results of the validation study with CI users revealed no significant differences in percent correct scores for 29 of the 33 sentence lists. However, individual listeners demonstrated considerable variability in performance on the 29 lists. The binomial distribution model was used to account for the inherent variability observed in the lists. This model was also used to generate 95% confidence intervals for one and two list comparisons. A retrospective analysis of 172 instances where research subjects had been tested on two lists within a single condition revealed that 94% of results were accurately contained within these confidence intervals. CONCLUSIONS: The use of a five-channel CI simulation to estimate the intelligibility of individual sentences allowed for the creation of a large number of sentence lists with an equivalent level of difficulty. The results of the validation procedure with CI users found that 29 of 33 lists allowed scores that were not statistically different. However, individual listeners demonstrated considerable variability in performance across lists. This variability was accurately described by the binomial distribution model and was used to estimate the magnitude of change required to achieve statistical significance when comparing scores from one and two lists per condition. Fifteen sentence lists have been included in the AzBio Sentence Test for use in the clinical evaluation of hearing-impaired listeners and CI users. An additional eight sentence lists have been included in the Minimum Speech Test Battery to be distributed by the CI manufacturers for the evaluation of CI candidates.

HEARING, PSYCHOPHYSICS, AND COCHLEAR IMPLANTATION: EXPERIENCES OF OLDER INDIVIDUALS WITH MILD SLOPING TO PROFOUND SENSORY HEARING LOSS.

In a previous paper we reported the frequency selectivity, temporal resolution, nonlinear cochlear processing, and speech recognition in quiet and in noise for 5 listeners with normal hearing (mean age 24.2 years) and 17 older listeners (mean age 68.5 years) with bilateral, mild sloping to profound sensory hearing loss (Gifford et al., 2007). Since that report, 2 additional participants with hearing loss completed experimentation for a total of 19 listeners. Of the 19 with hearing loss, 16 ultimately received a cochlear implant. The purpose of the current study was to provide information on the pre-operative psychophysical characteristics of low-frequency hearing and speech recognition abilities, and on the resultant postoperative speech recognition and associated benefit from cochlear implantation. The current preoperative data for the 16 listeners receiving cochlear implants demonstrate: 1) reduced or absent nonlinear cochlear processing at 500 Hz, 2) impaired frequency selectivity at 500 Hz, 3) normal temporal resolution at low modulation rates for a 500-Hz carrier, 4) poor speech recognition in a modulated background, and 5) highly variable speech recognition (from 0 to over 60% correct) for monosyllables in the bilaterally aided condition. As reported previously, measures of auditory function were not significantly correlated with pre- or post-operative speech recognition - with the exception of nonlinear cochlear processing and preoperative sentence recognition in quiet (p=0.008) and at +10 dB SNR (p=0.007). These correlations, however, were driven by the data obtained from two listeners who had the highest degree of nonlinearity and preoperative sentence recognition. All estimates of postoperative speech recognition performance were significantly higher than preoperative estimates for both the ear that was implanted (p<0.001) as well as for the best-aided condition (p<0.001). It can be concluded that older individuals with mild sloping to profound sensory hearing loss have very little to no residual nonlinear cochlear function, resulting in impaired frequency selectivity as well as poor speech recognition in modulated noise. These same individuals exhibit highly significant improvement in speech recognition in both quiet and noise following cochlear implantation. For older individuals with mild to profound sensorineural hearing loss who have difficulty in speech recognition with appropriately fitted hearing aids, there is little to lose in terms of psychoacoustic processing in the low-frequency region and much to gain with respect to speech recognition and overall communication benefit. These data further support the need to consider factors beyond the audiogram in determining cochlear implant candidacy, as older individuals with relatively good low-frequency hearing may exhibit vastly different speech perception abilities - illustrating the point that signal audibility is not a reliable predictor of performance on supra-threshold tasks such as speech recognition.

Information from the voice fundamental frequency (F0) region accounts for the majority of the benefit when acoustic stimulation is added to electric stimulation.

OBJECTIVES: The aim of this study was to determine the minimum amount of low-frequency acoustic information that is required to achieve speech perception benefit in listeners with a cochlear implant in one ear and low-frequency hearing in the other ear. DESIGN: The recognition of monosyllabic words in quiet and sentences in noise was evaluated in three listening conditions: electric stimulation alone, acoustic stimulation alone, and combined electric and acoustic stimulation. The acoustic stimuli presented to the nonimplanted ear were either low-pass-filtered at 125, 250, 500, or 750 Hz, or unfiltered (wideband). RESULTS: Adding low-frequency acoustic information to electrically stimulated information led to a significant improvement in word recognition in quiet and sentence recognition in noise. Improvement was observed in the electric and acoustic stimulation condition even when the acoustic information was limited to the 125-Hz-low-passed signal. Further improvement for the sentences in noise was observed when the acoustic signal was increased to wideband. CONCLUSIONS: Information from the voice fundamental frequency (F0) region accounts for the majority of the speech perception benefit when acoustic stimulation is added to electric stimulation. We propose that, in quiet, low-frequency acoustic information leads to an improved representation of voicing, which in turn leads to a reduction in word candidates in the lexicon. In noise, the robust representation of voicing allows access to low-frequency acoustic landmarks that mark syllable structure and word boundaries. These landmarks can bootstrap word and sentence recognition.

Frequency overlap between electric and acoustic stimulation and speech-perception benefit in patients with combined electric and acoustic stimulation.

OBJECTIVES: Our aim was to assess, for patients with a cochlear implant in one ear and low-frequency acoustic hearing in the contralateral ear, whether reducing the overlap in frequencies conveyed in the acoustic signal and those analyzed by the cochlear implant speech processor would improve speech recognition. DESIGN: The recognition of monosyllabic words in quiet and sentences in noise was evaluated in three listening configurations: electric stimulation alone, acoustic stimulation alone, and combined electric and acoustic stimulation. The acoustic stimuli were either unfiltered or low-pass (LP) filtered at 250, 500, or 750 Hz. The electric stimuli were either unfiltered or high-pass (HP) filtered at 250, 500, or 750 Hz. In the combined condition, the unfiltered acoustic signal was paired with the unfiltered electric signal, the 250-Hz LP acoustic signal was paired with the 250-Hz HP electric signal, the 500-Hz LP acoustic signal was paired with the 500-Hz HP electric signal, and the 750-Hz LP acoustic signal was paired with the 750-Hz HP electric signal. RESULTS: For both acoustic and electric signals, performance increased as the bandwidth increased. The highest level of performance in the combined condition was observed in the unfiltered acoustic plus unfiltered electric condition. CONCLUSIONS: Reducing the overlap in frequency representation between acoustic and electric stimulation does not increase speech understanding scores for patients who have residual hearing in the ear contralateral to the implant. We find that acoustic information <250 Hz significantly improves performance for patients who combine electric and acoustic stimulation and accounts for the majority of the speech-perception benefit when acoustic stimulation is combined with electric stimulation.

Spectral modulation detection and vowel and consonant identifications in cochlear implant listeners.

Speech understanding by cochlear implant listeners may be limited by their ability to perceive complex spectral envelopes. Here, spectral envelope perception was characterized by spectral modulation transfer functions in which modulation detection thresholds became poorer with increasing spectral modulation frequency (SMF). Thresholds at low SMFs, less likely to be influenced by spectral resolution, were correlated with vowel and consonant identifications [Litvak, L. M. et al. (2008). J. Acoust. Soc. Am. 122, 982-991] for the same listeners; while thresholds at higher SMFs, more likely to be affected by spectral resolution, were not. Results indicate that the perception of broadly spaced spectral features is important for speech perception.

Hearing preservation surgery: psychophysical estimates of cochlear damage in recipients of a short electrode array.

In the newest implementation of cochlear implant surgery, electrode arrays of 10 or 20 mm are inserted into the cochlea with the aim of preserving hearing in the region apical to the tip of the electrode array. In the current study two measures were used to assess hearing preservation: changes in audiometric threshold and changes in psychophysical estimates of nonlinear cochlear processing. Nonlinear cochlear processing was evaluated at signal frequencies of 250 and 500 Hz using Schroeder phase maskers with various indices of masker phase curvature. A total of 15 normal-hearing listeners and 13 cochlear implant patients (7 with a 10 mm insertion and 6 with a 20 mm insertion) were tested. Following surgery the mean low-frequency threshold elevation was 12.7 dB (125-750 Hz). Nine patients had postimplant thresholds within 5-10 dB of preimplant thresholds. Only one patient, however, demonstrated a completely normal nonlinear cochlear function following surgery--although most retained some degree of residual nonlinear processing. This result indicates (i) that Schroeder phase masking functions are a more sensitive index of surgical trauma than audiometric threshold and (ii) that preservation of a normal cochlear function in the apex of the cochlea is relatively uncommon but possible.

Simulating the effects of spread of electric excitation on musical tuning and melody identification with a cochlear implant.

PURPOSE: To determine why, in a pilot study, only 1 of 11 cochlear implant listeners was able to reliably identify a frequency-to-electrode map where the intervals of a familiar melody were played on the correct musical scale. The authors sought to validate their method and to assess the effect of pitch strength on musical scale recognition in normal-hearing listeners. METHOD: Musical notes were generated as either sine waves or spectrally shaped noise bands, with a center frequency equal to that of a desired note and symmetrical (log-scale) reduction in amplitude away from the center frequency. The rate of amplitude reduction was manipulated to vary pitch strength of the notes and to simulate different degrees of current spread. The effect of the simulated degree of current spread was assessed on tasks of musical tuning/scaling, melody recognition, and frequency discrimination. RESULTS: Normal-hearing listeners could accurately and reliably identify the appropriate musical scale when stimuli were sine waves or steeply sloping noise bands. Simulating greater current spread degraded performance on all tasks. CONCLUSIONS: Cochlear implant listeners with an auditory memory of a familiar melody could likely identify an appropriate frequency-to-electrode map but only in cases where the pitch strength of the electrically produced notes is very high.

The benefits of combining acoustic and electric stimulation for the recognition of speech, voice and melodies.

Fifteen patients fit with a cochlear implant in one ear and a hearing aid in the other ear were presented with tests of speech and melody recognition and voice discrimination under conditions of electric (E) stimulation, acoustic (A) stimulation and combined electric and acoustic stimulation (EAS). When acoustic information was added to electrically stimulated information performance increased by 17-23 percentage points on tests of word and sentence recognition in quiet and sentence recognition in noise. On average, the EAS patients achieved higher scores on CNC words than patients fit with a unilateral cochlear implant. While the best EAS patients did not outperform the best patients fit with a unilateral cochlear implant, proportionally more EAS patients achieved very high scores on tests of speech recognition than unilateral cochlear implant patients.

Effect of digital frequency compression (DFC) on speech recognition in candidates for combined electric and acoustic stimulation (EAS).

PURPOSE: To compare the effects of conventional amplification (CA) and digital frequency compression (DFC) amplification on the speech recognition abilities of candidates for a partial-insertion cochlear implant, that is, candidates for combined electric and acoustic stimulation (EAS). METHOD: The participants were 6 patients whose audiometric thresholds at 500 Hz and below were or=80 dB HL. Six tests of speech understanding were administered with CA and DFC. The Abbreviated Profile of Hearing Aid Benefit (APHAB) was also administered following use of CA and DFC. RESULTS: Group mean scores were not statistically different in the CA and DFC conditions. However, 2 patients received substantial benefit in DFC conditions. APHAB scores suggested increased ease of communication, but also increased aversive sound quality. CONCLUSION: Results suggest that a relatively small proportion of individuals who meet EAS candidacy will receive substantial benefit from a DFC hearing aid and that a larger proportion will receive at least a small benefit when speech is presented against a background of noise. This benefit, however, comes at a cost-aversive sound quality.

Loudness growth observed under partially tripolar stimulation: model and data from cochlear implant listeners.

Most cochlear implant strategies utilize monopolar stimulation, likely inducing relatively broad activation of the auditory neurons. The spread of activity may be narrowed with a tripolar stimulation scheme, wherein compensating current of opposite polarity is simultaneously delivered to two adjacent electrodes. In this study, a model and cochlear implant subjects were used to examine loudness growth for varying amounts of tripolar compensation, parameterized by a coefficient sigma, ranging from 0 (monopolar) to 1 (full tripolar). In both the model and the subjects, current required for threshold activation could be approximated by I(sigma)=Ithr(0)(1-sigmaK), with fitted constants Ithr(0) and K. Three of the subjects had a "positioner," intended to place their electrode arrays closer to their neural tissue. The values of K were smaller for the positioner users and for a "close" electrode-to-tissue distance in the model. Above threshold, equal-loudness contours for some subjects deviated significantly from a linear scale-up of the threshold approximations. The patterns of deviation were similar to those observed in the model for conditions in which most of the neurons near the center electrode were excited.

Relationship between perception of spectral ripple and speech recognition in cochlear implant and vocoder listeners.

Spectral resolution has been reported to be closely related to vowel and consonant recognition in cochlear implant (CI) listeners. One measure of spectral resolution is spectral modulation threshold (SMT), which is defined as the smallest detectable spectral contrast in the spectral ripple stimulus. SMT may be determined by the activation pattern associated with electrical stimulation. In the present study, broad activation patterns were simulated using a multi-band vocoder to determine if similar impairments in speech understanding scores could be produced in normal-hearing listeners. Tokens were first decomposed into 15 logarithmically spaced bands and then re-synthesized by multiplying the envelope of each band by matched filtered noise. Various amounts of current spread were simulated by adjusting the drop-off of the noise spectrum away from the peak (40-5 dBoctave). The average SMT (0.25 and 0.5 cyclesoctave) increased from 6.3 to 22.5 dB, while average vowel identification scores dropped from 86% to 19% and consonant identification scores dropped from 93% to 59%. In each condition, the impairments in speech understanding were generally similar to those found in CI listeners with similar SMTs, suggesting that variability in spread of neural activation largely accounts for the variability in speech perception of CI listeners.

Combined electric and contralateral acoustic hearing: word and sentence recognition with bimodal hearing.

PURPOSE: The authors assessed whether (a) a full-insertion cochlear implant would provide a higher level of speech understanding than bilateral low-frequency acoustic hearing, (b) contralateral acoustic hearing would add to the speech understanding provided by the implant, and (c) the level of performance achieved with electric stimulation plus contralateral acoustic hearing would be similar to performance reported in the literature for patients with a partial insertion cochlear implant. METHOD: Monosyllabic word recognition as well as sentence recognition in quiet and at +10 and +5 dB was assessed. Before implantation, scores were obtained in monaural and binaural conditions. Following implantation, scores were obtained in electric-only and electric-plus-contralateral acoustic conditions. RESULTS: Postoperatively, all individuals achieved higher scores in the electric-only test conditions than they did in the best pre-implant test conditions. All individuals benefited from the addition of low-frequency information to the electric hearing. CONCLUSION: A full-insertion cochlear implant provides better speech understanding than bilateral, low-frequency residual hearing. The combination of an implant and contralateral acoustic hearing yields comparable performance to that of patients with a partially inserted implant and bilateral, low-frequency acoustic hearing. These data suggest that a full-insertion cochlear implant is a viable treatment option for patients with low-frequency residual hearing.

Auditory function and speech understanding in listeners who qualify for EAS surgery.

OBJECTIVE: For patients with relatively good low-frequency hearing and relatively poor high-frequency hearing, who met the pre-implant criteria for combined electric and acoustic stimulation (EAS), our aims were to i) assess deficits in low-frequency auditory function, ii) to identify measures which might be sensitive to changes resulting from the insertion of an intracochlear electrode array, and iii) to quantify the relationship between measures of auditory function and performance on tasks of speech and melody recognition. DESIGN: Measures of frequency selectivity, temporal resolution, and nonlinear cochlear function, along with measures of word, sentence, consonant, vowel, and melody recognition, were obtained from 5 normal-hearing and 17 hearing-impaired listeners. The hearing-impaired listeners had auditory thresholds at 500 Hz, ranging from 20 to 60 dB HL, and thresholds at 1 kHz, ranging from 60 to 100 dB HL. RESULTS: Nonlinear cochlear function was either reduced or absent. Frequency selectivity at 500 Hz was significantly reduced but still present in most patients. Temporal resolution, when measured at low modulation frequencies, was normal. Speech recognition in a modulated background revealed significantly poorer performance than normal. Speech and melody recognition varied over a large range. No measure of auditory function was correlated significantly with speech recognition. However, frequency selectivity was related to melody recognition. CONCLUSIONS: (1) Patients who qualify for EAS surgery have a wide range of speech and melody recognition abilities. (2) A number of the psychophysical measures tested may prove more sensitive than the audiogram in determining the degree of damage inflicted by the intracochlear electrode array. (3) Speech recognition was not correlated with any of the measures of auditory function.

Performance of patients using different cochlear implant systems: effects of input dynamic range.

OBJECTIVE: To determine, for patients who had identical levels of performance on a monosyllabic word test presented in quiet, whether device differences would affect performance when tested with other materials and in other test conditions. DESIGN: For Experiment 1, from a test population of 76 patients, three groups (N = 13 in each group) were created. Patients in the first group used the CII Bionic Ear behind-the-ear (BTE) speech processor, patients in the second group used the Esprit3G BTE speech processor, and patients in the third group used the Tempo+ BTE speech processor. The patients in each group were matched on (i) monosyllabic word scores in quiet, (ii) age at testing, (iii) duration of deafness, and (iv) experience with their device. Performance of the three groups was compared on a battery of tests of speech understanding, voice discrimination, and melody recognition. In Experiments 2 (N = 10) and 3 (N = 10) the effects of increasing input dynamic range in the 3G and CII devices, respectively, was assessed with sentence material presented at conversational levels in quiet, conversational levels in noise, and soft levels in quiet. RESULTS: Experiment 1 revealed that patients fit with the CII processor achieved higher scores than Esprit3G and Tempo+ patients on tests of vowel recognition. CII and Tempo+ patients achieved higher scores than Esprit3G patients on difficult sentence material presented in noise at +10 and +5 dB SNR. CII patients achieved higher scores than Esprit3G patients on difficult sentence material presented at a soft level (54 dB SPL). Experiment 2 revealed that increasing input dynamic range in the Esprit3G device had (i) no effect at conversational levels in quiet, (ii) degraded performance in noise, and (iii) improved performance at soft levels. Experiment 3 revealed that increasing input dynamic range in the CII device improved performance in all conditions. CONCLUSIONS: Differences in implant design can affect patient performance, especially in difficult listening situations. Input dynamic range and the method by which compression is implemented appear to be the major factors that account for our results.