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Cochlear dead regions constrain the benefit of combining acoustic stimulation with electric stimulation.

ABSTRACT: The aims of this study were to (1) detect the presence and edge frequency (fe) of a cochlear dead region in the ear with residual acoustic hearing for bimodal cochlear implant users, and (2) determine whether amplification based on the presence or absence of a dead region would improve speech understanding and sound quality.Twenty-two listeners with a cochlear implant in one ear and residual acoustic hearing in the nonimplanted ear were tested. Eleven listeners had a cochlear dead region in the acoustic-hearing ear and 11 did not. Dead regions were assessed with the threshold-equalizing noise (TEN) and the sweeping noise, psychophysical tuning curve tests. Speech understanding was assessed with monosyllabic words and the AzBio sentences at +10 dB signal-to-noise ratio. Speech- and music-quality judgments were obtained with the Judgment of Sound Quality questionnaire.Using shifted tips of the psychophysical tuning curve as a basis for diagnosis, the TEN had high sensitivity (0.91) and poor specificity (0.55) for this population. The value of fe was lower when estimated with the sweeping noise, psychophysical tuning curve test than with the TEN test. For the listeners with cochlear dead regions, speech understanding, speech quality and music quality were best when no amplification was applied for frequencies within the dead region. For listeners without dead regions, speech understanding was best with full-bandwidth amplification and was reduced when amplification was not applied when the audiometric threshold exceeded 80 dB HL.The data from this study suggest that, to improve bimodal benefit for listeners who combine electric and acoustic stimulation, audiologists should routinely test for the presence of cochlear dead regions and determine amplification bandwidth accordingly.

SUBMITTER: Zhang T

PROVIDER: S-EPMC4066196 | biostudies-literature | 2014 Jul-Aug

REPOSITORIES: biostudies-literature

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Cochlear dead regions constrain the benefit of combining acoustic stimulation with electric stimulation.

Zhang Ting T Dorman Michael F MF Gifford Rene R Moore Brian C J BC

Ear and hearing 20140701 4

<h4>Objective</h4>The aims of this study were to (1) detect the presence and edge frequency (fe) of a cochlear dead region in the ear with residual acoustic hearing for bimodal cochlear implant users, and (2) determine whether amplification based on the presence or absence of a dead region would improve speech understanding and sound quality.<h4>Design</h4>Twenty-two listeners with a cochlear implant in one ear and residual acoustic hearing in the nonimplanted ear were tested. Eleven listeners h ...[more]

PMID: 24950254

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Project description:OBJECTIVE:The primary objective of this study was to assess the effect of electric and acoustic overlap for speech understanding in typical listening conditions using semidiffuse noise. DESIGN:This study used a within-subjects, repeated measures design including 11 experienced adult implant recipients (13 ears) with functional residual hearing in the implanted and nonimplanted ear. The aided acoustic bandwidth was fixed and the low-frequency cutoff for the cochlear implant (CI) was varied systematically. Assessments were completed in the R-SPACE sound-simulation system which includes a semidiffuse restaurant noise originating from eight loudspeakers placed circumferentially about the subject's head. AzBio sentences were presented at 67 dBA with signal to noise ratio varying between +10 and 0 dB determined individually to yield approximately 50 to 60% correct for the CI-alone condition with full CI bandwidth. Listening conditions for all subjects included CI alone, bimodal (CI + contralateral hearing aid), and bilateral-aided electric and acoustic stimulation (EAS; CI + bilateral hearing aid). Low-frequency cutoffs both below and above the original "clinical software recommendation" frequency were tested for all patients, in all conditions. Subjects estimated listening difficulty for all conditions using listener ratings based on a visual analog scale. RESULTS:Three primary findings were that (1) there was statistically significant benefit of preserved acoustic hearing in the implanted ear for most overlap conditions, (2) the default clinical software recommendation rarely yielded the highest level of speech recognition (1 of 13 ears), and (3) greater EAS overlap than that provided by the clinical recommendation yielded significant improvements in speech understanding. CONCLUSIONS:For standard-electrode CI recipients with preserved hearing, spectral overlap of acoustic and electric stimuli yielded significantly better speech understanding and less listening effort in a laboratory-based, restaurant-noise simulation. In conclusion, EAS patients may derive more benefit from greater acoustic and electric overlap than given in current software fitting recommendations, which are based solely on audiometric threshold. These data have larger scientific implications, as previous studies may not have assessed outcomes with optimized EAS parameters, thereby underestimating the benefit afforded by hearing preservation.

Project description:BackgroundHarmony is an important part of tonal music that conveys context, form and emotion. Two notes sounded simultaneously form a harmonic interval. In normal-hearing (NH) listeners, some harmonic intervals (e.g., minor 2nd, tritone, major 7th) typically sound more dissonant than others (e.g., octave, major 3rd, 4th). Because of the limited spectro-temporal resolution afforded by cochlear implants (CIs), music perception is generally poor. However, CI users may still be sensitive to relative dissonance across intervals. In this study, dissonance ratings for harmonic intervals were measured in 11 unilaterally deaf CI patients, in whom ratings from the CI could be compared to those from the normal ear.MethodsStimuli consisted of pairs of equal amplitude MIDI piano tones. Intervals spanned a range of two octaves relative to two root notes (F3 or C4). Dissonance was assessed in terms of subjective pleasantness ratings for intervals presented to the NH ear alone, the CI ear alone, and both ears together (NH + CI). Ratings were collected for both root notes for within- and across-octave intervals (1-12 and 13-24 semitones). Participants rated the pleasantness of each interval by clicking on a line anchored with "least pleasant" and "most pleasant." A follow-up experiment repeated the task with a smaller stimulus set.ResultsWith NH-only listening, within-octave intervals minor 2nd, major 2nd, and major 7th were rated least pleasant; major 3rd, 5th, and octave were rated most pleasant. Across-octave counterparts were similarly rated. With CI-only listening, ratings were consistently lower and showed a reduced range. Mean ratings were highly correlated between NH-only and CI-only listening (r = 0.845, p < 0.001). Ratings were similar between NH-only and NH + CI listening, with no significant binaural enhancement/interference. The follow-up tests showed that ratings were reliable for the least and most pleasant intervals.DiscussionAlthough pleasantness ratings were less differentiated for the CI ear than the NH ear, there were similarities between the two listening modes. Given the lack of spectro-temporal detail needed for harmonicity-based distinctions, temporal envelope interactions (within and across channels) associated with a perception of roughness may contribute to dissonance perception for harmonic intervals with CI-only listening.

Project description:The aim of this study was to assess the frequency-position function resulting from electric stimulation of electrodes in cochlear implant subjects with significant residual hearing in their nonimplanted ear. Six cochlear implant users compared the pitch of the auditory sensation produced by stimulation of an intracochlear electrode to the pitch of acoustic pure tones presented to their contralateral nonimplanted ear. Subjects were implanted with different Clarion electrode arrays, designed to lie close to the inner wall of the cochlea. High-resolution radiographs were used to determine the electrode positions in the cochlea. Four out of six subjects presented electrode insertions deeper than 450 degrees . We used a two-interval (one acoustic, one electric), two-alternative forced choice protocol (2I-2AFC), asking the subject to indicate which stimulus sounded the highest in pitch. Pure tones were used as acoustic stimuli. Electric stimuli consisted of trains of biphasic pulses presented at relatively high rates [higher than 700 pulses per second (pps)]. First, all electric stimuli were balanced in loudness across electrodes. Second, acoustic pure tones, chosen to approximate roughly the pitch sensation produced by each electrode, were balanced in loudness to electric stimuli. When electrode insertion lengths were used to describe electrode positions, the pitch sensations produced by electric stimulation were found to be more than two octaves lower than predicted by Greenwood's frequency-position function. When insertion angles were used to describe electrode positions, the pitch sensations were found about one octave lower than the frequency-position function of a normal ear. The difference found between both descriptions is because of the fact that these electrode arrays were designed to lie close to the modiolus. As a consequence, the site of excitation produced at the level of the organ of Corti corresponds to a longer length than the electrode insertion length, which is used in Greenwood's function. Although exact measurements of the round window position as well as the length of the cochlea could explain the remaining one octave difference found when insertion angles were used, physiological phenomena (e.g., stimulation of the spiral ganglion cells) could also create this difference. From these data, analysis filters could be determined in sound coding strategies to match the pitch percepts elicited by electrode stimulation. This step might be of main importance for music perception and for the fitting of bilateral cochlear implants.

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Cochlear dead regions constrain the benefit of combining acoustic stimulation with electric stimulation.

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Cochlear dead regions constrain the benefit of combining acoustic stimulation with electric stimulation.

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