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Purpose: For bilaterally implanted patients, the automatic gain control (AGC) in both left and right cochlear implant (CI) processors is usually neither linked nor synchronized. At high AGC compression ratios, this lack of coordination between the two processors can distort interaural level differences, the only useful interaural difference cue available to CI patients. This study assessed the improvement, if any, in the utility of interaural level differences for sound source localization in the frontal hemifield when AGCs were synchronized versus independent and when listeners were stationary versus allowed to move their heads. Method: Sound source identification of broadband noise stimuli was tested for seven bilateral CI patients using 13 loudspeakers in the frontal hemifield, under conditions where AGCs were linked and unlinked. For half the conditions, patients remained stationary; in the other half, they were encouraged to rotate or reorient their heads within a range of approximately ± 30° during sound presentation. Results: In general, those listeners who already localized reasonably well with independent AGCs gained the least from AGC synchronization, perhaps because there was less room for improvement. Those listeners who performed worst with independent AGCs gained the most from synchronization. All listeners performed as well or better with synchronization than without; however, intersubject variability was high. Head movements had little impact on the effectiveness of synchronization of AGCs. Conclusion: Synchronization of AGCs offers one promising strategy for improving localization performance in the frontal hemifield for bilaterally implanted CI patients.

Purpose: Our aim was to make audible for normal-hearing listeners the Mickey Mouse™ sound quality of cochlear implants (CIs) often found following device activation. Method: The listeners were 3 single-sided deaf patients fit with a CI and who had 6 months or less of CI experience. Computed tomography imaging established the location of each electrode contact in the cochlea and allowed an estimate of the place frequency of the tissue nearest each electrode. For the most apical electrodes, this estimate ranged from 650 to 780 Hz. To determine CI sound quality, a clean signal (a sentence) was presented to the CI ear via a direct connect cable and candidate, and CI-like signals were presented to the ear with normal hearing via an insert receiver. The listeners rated the similarity of the candidate signals to the sound of the CI on a 1- to 10-point scale, with 10 being a complete match. Results: To make the match to CI sound quality, all 3 patients need an upshift in formant frequencies (300-800 Hz) and a metallic sound quality. Two of the 3 patients also needed an upshift in voice pitch (10-80 Hz) and a muffling of sound quality. Similarity scores ranged from 8 to 9.7. Conclusion: The formant frequency upshifts, fundamental frequency upshifts, and metallic sound quality experienced by the listeners can be linked to the relatively basal locations of the electrode contacts and short duration experience with their devices. The perceptual consequence was not the voice quality of Mickey Mouse™ but rather that of Munchkins in "The Wizard of Oz" for whom both formant frequencies and voice pitch were upshifted.

Purpose: The primary purpose of this study was to assess speech understanding in quiet and in diffuse noise for adult cochlear implant (CI) recipients utilizing bimodal hearing or bilateral CIs. Our primary hypothesis was that bilateral CI recipients would demonstrate less effect of source azimuth in the bilateral CI condition due to symmetric interaural head shadow. Method: Sentence recognition was assessed for adult bilateral (n = 25) CI users and bimodal listeners (n = 12) in three conditions: (1) source location certainty regarding fixed target azimuth, (2) source location uncertainty regarding roving target azimuth, and (3) Condition 2 repeated, allowing listeners to turn their heads, as needed. Results: (a) Bilateral CI users exhibited relatively similar performance regardless of source azimuth in the bilateral CI condition; (b) bimodal listeners exhibited higher performance for speech directed to the better hearing ear even in the bimodal condition; (c) the unilateral, better ear condition yielded higher performance for speech presented to the better ear versus speech to the front or to the poorer ear; (d) source location certainty did not affect speech understanding performance; and (e) head turns did not improve performance. The results confirmed our hypothesis that bilateral CI users exhibited less effect of source azimuth than bimodal listeners. That is, they exhibited similar performance for speech recognition irrespective of source azimuth, whereas bimodal listeners exhibited significantly poorer performance with speech originating from the poorer hearing ear (typically the nonimplanted ear). Conclusions: Bilateral CI users overcame ear and source location effects observed for the bimodal listeners. Bilateral CI users have access to head shadow on both sides, whereas bimodal listeners generally have interaural asymmetry in both speech understanding and audible bandwidth limiting the head shadow benefit obtained from the poorer ear (generally the nonimplanted ear). In summary, we found that, in conditions with source location uncertainty and increased ecological validity, bilateral CI performance was superior to bimodal listening.

Purpose: The aim of this article is to summarize recent published and unpublished research from our 2 laboratories on improving speech understanding in complex listening environments by listeners fit with cochlear implants (CIs). Method: CI listeners were tested in 2 listening environments. One was a simulation of a restaurant with multiple, diffuse noise sources, and the other was a cocktail party with 2 spatially separated point sources of competing speech. At issue was the value of the following sources of information, or interventions, on speech understanding: (a) visual information, (b) adaptive beamformer microphones and remote microphones, (c) bimodal fittings, that is, a CI and contralateral low-frequency acoustic hearing, (d) hearing preservation fittings, that is, a CI with preserved low-frequency acoustic in the same ear plus low-frequency acoustic hearing in the contralateral ear, and (e) bilateral CIs. Results: A remote microphone provided the largest improvement in speech understanding. Visual information and adaptive beamformers ranked next, while bimodal fittings, bilateral fittings, and hearing preservation provided significant but less benefit than the other interventions or sources of information. Only bilateral CIs allowed listeners high levels of speech understanding when signals were roved over the frontal plane. Conclusions: The evidence supports the use of bilateral CIs and hearing preservation surgery for best speech understanding in complex environments. These fittings, when combined with visual information and microphone technology, should lead to high levels of speech understanding by CI patients in complex listening environments.

Purpose: The aim of this experiment was to compare, for patients with cochlear implants (CIs), the improvement for speech understanding in noise provided by a monaural adaptive beamformer and for two interventions that produced bilateral input (i.e., bilateral CIs and hearing preservation [HP] surgery). Method: Speech understanding scores for sentences were obtained for 10 listeners fit with a single CI. The listeners were tested with and without beamformer activated in a "cocktail party" environment with spatially separated target and maskers. Data for 10 listeners with bilateral CIs and 8 listeners with HP CIs were taken from Loiselle, Dorman, Yost, Cook, and Gifford (2016), who used the same test protocol. Results: The use of the beamformer resulted in a 31 percentage point improvement in performance; in bilateral CIs, an 18 percentage point improvement; and in HP CIs, a 20 percentage point improvement. Conclusion: A monaural adaptive beamformer can produce an improvement in speech understanding in a complex noise environment that is equal to, or greater than, the improvement produced by bilateral CIs and HP surgery.

Purpose: Five experiments probed auditory-visual (AV) understanding of sentences by users of cochlear implants (CIs). Method: Sentence material was presented in auditory (A), visual (V), and AV test conditions to listeners with normal hearing and CI users. Results: (a) Most CI users report that most of the time, they have access to both A and V information when listening to speech. (b) CI users did not achieve better scores on a task of speechreading than did listeners with normal hearing. (c) Sentences that are easy to speechread provided 12 percentage points more gain to speech understanding than did sentences that were difficult. (d) Ease of speechreading for sentences is related to phrase familiarity. (e) Users of bimodal CIs benefit from low-frequency acoustic hearing even when V cues are available, and a second CI adds to the benefit of a single CI when V cues are available. (f) V information facilitates lexical segmentation by improving the recognition of the number of syllables produced and the relative strength of these syllables. Conclusions: Our data are consistent with the view that V information improves CI users' ability to identify syllables in the acoustic stream and to recognize their relative juxtaposed strengths. Enhanced syllable resolution allows better identification of word onsets, which, when combined with place-of-articulation information from visible consonants, improves lexical access.

Purpose: To assess the role of interaural time differences and interaural level differences in (a) sound-source localization, and (b) speech understanding in a cocktail party listening environment for listeners with bilateral cochlear implants (CIs) and for listeners with hearing-preservation CIs. Methods: Eleven bilateral listeners with MED-EL (Durham, NC) CIs and 8 listeners with hearing-preservation CIs with symmetrical low frequency, acoustic hearing using the MED-EL or Cochlear device were evaluated using 2 tests designed to task binaural hearing, localization, and a simulated cocktail party. Access to interaural cues for localization was constrained by the use of low-pass, high-pass, and wideband noise stimuli. Results: Sound-source localization accuracy for listeners with bilateral CIs in response to the high-pass noise stimulus and sound-source localization accuracy for the listeners with hearing-preservation CIs in response to the low-pass noise stimulus did not differ significantly. Speech understanding in a cocktail party listening environment improved for all listeners when interaural cues, either interaural time difference or interaural level difference, were available. Conclusions: The findings of the current study indicate that similar degrees of benefit to sound-source localization and speech understanding in complex listening environments are possible with 2 very different rehabilitation strategies: the provision of bilateral CIs and the preservation of hearing.

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.

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 less than or equal to 60 dB HL and whose thresholds at 2000 Hz and above were greater than or equal to 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. (Contains 5 figures, 1 table and 1 footnote.)

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.

Vowels, consonants, and sentences were processed by two cochlear-implant signal-processing strategies--a fixed-channel strategy and a channel-picking strategy--and the resulting signals were presented to listeners with normal hearing for identification. At issue was the number of channels of stimulation needed in each strategy to achieve an equivalent level of speech recognition in quiet and in noise. In quiet, 8 fixed channels allowed a performance maximum for the most difficult stimulus material. A similar level of performance was reached with a 6-of-20 channel-picking strategy. In noise, 10 fixed channels allowed a performance maximum for the most difficult stimulus material. A similar level of performance was reached with a 9-of-20 strategy. Both strategies are capable of providing a very high level of speech recognition. Choosing between the two strategies may, ultimately, depend on issues that are independent of speech recognition--such as ease of device programming. KEY WORDS: cochlear implants, acoustic models, signal processing, adults, Modern cochlear implants provide two strategies for coding speech (e.g., McDermott, McKay, & Vandali, 1992; Wilson et al., 1991; for reviews, see Loizou, 1998, and Wilson, 2000). Fixed-channel strategies use [...]

Listeners judged the dissimilarity of pairs of synthesized nasal voices that varied on 3 dimensions. Separate nonmetric multidimensional scaling (MDS) solutions were calculated for each listener and the group. Similar 3-dimensional solutions were derived for the group and each of the listeners, with the group MDS solution accounting for 83% of the total variance in listeners' judgments. Dimension 1 ("Nasality") accounted for 54% of the variance, Dimension 2 ("Loudness") for 18% of the variance, and Dimension 3 ("Pitch") for 11% of the variance. The 3 dimensions were significantly and positively correlated with objective measures of nasalization, intensity, and fundamental frequency. The results of this experiment are discussed in relation to other MDS studies of voice perception, and there is a discussion of methodological issues for future research. KEY WORDS: voice, perception, nasality, scaling, multidimensional, Most voice evaluation protocols require clinicians to make judgments about the pitch, loudness, quality, and resonance of the voice (American Speech-Language-Hearing Association, 1993; Boone & McFarlane, 1994). Various instruments have [...]

Several authors have evaluated consonant-to-vowel ratio (CVR) enhancement as a means to improve speech recognition in listeners with hearing impairment, with the intention of incorporating this approach into emerging amplification technology. Unfortunately, most previous studies have enhanced CVRs by increasing consonant energy, thus possibly confounding CVR effects with consonant audibility. In this study, we held consonant audibility constant by reducing vowel transition and steady-state energy rather than increasing consonant energy. Performance-by-intensity (PI) functions were obtained for recognition of voiceless stop consonants (/p/, /t/, /k/) presented in isolation (burst and aspiration digitally separated from the vowel) and for consonant-vowel syllables, with re-addition of the vowel /a/. There were three CVR conditions: normal CVR, vowel reduction by 6 dB, and vowel reduction by 12 dB. Testing was conducted in broadband noise fixed at 70 dB SPL and at 85 dB SPL. Six adults with sensorineural hearing impairment and 2 adults with normal hearing served as listeners. Results indicated that CVR enhancement did not improve identification performance when consonant audibility was held constant, except at the higher noise level for one listener with hearing impairment. The re-addition of the vowel energy to the isolated consonant did, however, produce large and significant improvements in phoneme identification. KEY WORDS: speech recognition, hearing impairment, amplification, signal processing, speech perception