Objectives This 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 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 2 female and 2 male talkers. The mean intelligibility of each sentence was estimated by processing each sentence through a 5-channel cochlear implant 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 cochlear implant users. Results Using sentence scores from the cochlear implant simulation study produced 33 lists of sentences with a mean score of 85% correct. The results of the validation study with cochlear implant 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 5-channel cochlear implant 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 cochlear implant 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 cochlear implant users. An additional 8 sentence lists have been included in the Minimum Speech Test Battery to be distributed by the cochlear implant manufacturers for the evaluation of cochlear implant candidates.

Objective: Our primary aim was to determine whether listeners in the following patient groups achieve localization accuracy within the 95th percentile of accuracy shown by younger or older normal-hearing (NH) listeners: (1) hearing impaired with bilateral hearing aids, (2) bimodal cochlear implant (CI), (3) bilateral CI, (4) hearing preservation CI, (5) single-sided deaf CI and (6) combined bilateral CI and bilateral hearing preservation. Design: The listeners included 57 young NH listeners, 12 older NH listeners, 17 listeners fit with hearing aids, 8 bimodal CI listeners, 32 bilateral CI listeners, 8 hearing preservation CI listeners, 13 single-sided deaf CI listeners and 3 listeners with bilateral CIs and bilateral hearing preservation. Sound source localization was assessed in a sound-deadened room with 13 loudspeakers arrayed in a 180-degree arc. Results: The root mean square (rms) error for the NH listeners was 6 degrees. The 95th percentile was 11 degrees. Nine of 16 listeners with bilateral hearing aids achieved scores within the 95th percentile of normal. Only 1 of 64 CI patients achieved a score within that range. Bimodal CI listeners scored at a level near chance, as did the listeners with a single CI or a single NH ear. Listeners with (1) bilateral CIs, (2) hearing preservation CIs, (3) single-sided deaf CIs and (4) both bilateral CIs and bilateral hearing preservation, all showed rms error scores within a similar range (mean scores between 20 and 30 degrees of error). Conclusion: Modern CIs do not restore a normal level of sound source localization for CI listeners with access to sound information from two ears.

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.

The aim of this study was to relate the pitch of high-rate electrical stimulation delivered to individual cochlear implant electrodes to electrode insertion depth and insertion angle. The patient (CH1) was able to provide pitch matches between electric and acoustic stimulation because he had auditory thresholds in his nonimplanted ear ranging between 30 and 60 dB HL over the range, 250 Hz to 8 kHz. Electrode depth and insertion angle were measured from high-resolution computed tomography (CT) scans of the patient_s temporal bones. The scans were used to create a 3D image volume reconstruction of the cochlea, which allowed visualization of electrode position within the scala. The method of limits was used to establish pitch matches between acoustic pure tones and electric stimulation (a 1,652-pps, unmodulated, pulse train). The pitch matching data demonstrated that, for insertion angles of greater than 450 degrees or greater than approximately 20 mm insertion depth, pitch saturated at approximately 420 Hz. From 20 to 15 mm insertion depth pitch estimates were about one-half octave lower than the Greenwood function. From 13 to 3 mm insertion depth the pitch estimates were approximately one octave lower than the Greenwood function. The pitch match for an electrode only 3.4 mm into the cochlea was 3,447 Hz. These data are consistent with other reports, e.g., Boëx et al. (2006), of a frequency-to-place map for the electrically stimulated cochlea in which perceived pitches for stimulation on individual electrodes are significantly lower than those predicted by the Greenwood function for stimulation at the level of the hair cell.

Objective The aims of this study were (i) to determine the magnitude of the interaural level differences (ILDs) that remain after cochlear implant (CI) signal processing and (ii) to relate the ILDs to the pattern of errors for sound source localization on the horizontal plane. Design The listeners were 16 bilateral CI patients fitted with MED-EL cochlear implants and 34 normal hearing listeners. The stimuli were wideband, high-pass and low-pass noise signals. ILDs were calculated by passing signals, filtered by head-related transfer functions (HRTFs), to a Matlab simulation of MED-EL signal processing. Results For the wideband signal and high-pass signals, maximum ILDs of 15–17dB in the input signal were reduced to 3–4dB after CI signal processing. For the low-pass signal, ILDs were reduced to 1–2dB. For wideband and high-pass signals, the largest ILDs for +/− 15 degree speaker locations were between .4 and .7dB; for the +/− 30 degree locations between .9 and 1.3dB; for the 45 degree locations between 2.4 and 2.9dB, for the +/− 60 degree locations, between 3.2 and 4.1dB and for the +/− 75 degree locations between 2.7 and 3.4dB. All of the CI patients in all stimulus conditions showed poorer localization than the normal hearing listeners. Localization accuracy for CI patients was best for the wideband and high-pass signals and was poorest for the low-pass signal. Conclusions Localization accuracy was related to the magnitude of the ILD cues available to the normal hearing listeners and CI patients. The pattern of localization errors for the CI patients was related to the magnitude of the ILD differences among loudspeaker locations. The error patterns for the wideband and high-pass signals, suggest that, for the conditions of this experiment, patients, on average, sorted signals on the horizontal plane into four sectors – on each side of the midline, one sector including 0, 15 and possibly 30 degrees, and a sector from 45 degrees to 75 degrees. Resolution within a sector was relatively poor.