Speech recognition was measured as a function of spectral resolution (number of spectral channels) and speech-to-noise ratio in normal-hearing (NH) and cochlear-implant (CI) listeners. Vowel, consonant, word, and sentence recognition were measured in five normal-hearing listeners, ten listeners with the Nucleus-22 cochlear implant, and nine listeners with the Advanced Bionics Clarion cochlear implant. Recognition was measured as a function of the number of spectral channels (noise bands or electrodes) at signal-to-noise ratios of + 15, + 10, +5, 0 dB, and in quiet. Performance with three different speech processing strategies (SPEAK, CIS, and SAS) was similar across all conditions, and improved as the number of electrodes increased (up to seven or eight) for all conditions. For all noise levels, vowel and consonant recognition with the SPEAK speech processor did not improve with more than seven electrodes, while for normal-hearing listeners, performance continued to increase up to at least 20 channels. Speech recognition on more difficult speech materials (word and sentence recognition) showed a marginally significant increase in Nucleus-22 listeners from seven to ten electrodes. The average implant score on all processing strategies was poorer than scores of NH listeners with similar processing. However, the best CI scores were similar to the normal-hearing scores for that condition (up to seven channels). CI listeners with the highest performance level increased in performance as the number of electrodes increased up to seven, while CI listeners with low levels of speech recognition did not increase in performance as the number of electrodes was increased beyond four. These results quantify the effect of number of spectral channels on speech recognition in noise and demonstrate that most CI subjects are not able to fully utilize the spectral information provided by the number of electrodes used in their implant.

1) Cortical evoked potentials elicited by naturally produced speech sounds can be reliably recorded in individuals. 2) Naturally produced speech tokens, representing different acoustic cues, evoke distinct neural response patterns. 3) Given the reliability of the response, this work has potential application to the study of neural processing of speech in individuals with communication disorders as well as changes over time after various types of auditory rehabilitation.

Speech-evoked cortical potentials can be recorded reliably in individuals during hearing aid use. A better understanding of how amplification (and device settings) affects neural response patterns is still needed.

The ACC can be reliably recorded in individuals wearing CI. Furthermore, the naturally produced speech syllables /si/ and /i/ evoke distinct ACC patterns. Because of its good stability and the ease with which it can be recorded in individual CI listeners, the ACC can be evoked using complex signals (such as naturally produced speech syllables) when studying central auditory function in CI listeners.

Cochlear implants have a significant suppressive effect on tinnitus in 66% of implant users. Although the reduction in the subjectively perceived tinnitus was statistically significant, it did not correlate with HINT; however, it did correlate with three quality-of-life domains, more significantly for those whose pretreatment conditions were moderate or worse.

Phoneme and speech recognition were measured as a function of stimulation pulse rate in 12 listeners with three types of cochlear implants. Identification of consonants and vowels and recognition of words and sentences were measured in 5 Clarion C1 subjects fit with continuous interleaved sampling (CIS) processors having 4 or 8 electrodes, 4 Nucleus 24 subjects fit with CIS processors having 4, 8, 12 or 16 electrodes and 3 Clarion C2 subjects fit with CIS processors with 4, 8, 12 and 16 electrodes. Stimulation rates ranged from 200 to more than 5000 Hz per electrode, depending on the device, number of electrodes used and stimulation strategy. Listeners were also tested on the same materials with their original processor prior to receiving the experimental processors. All testing was done in quiet listening conditions with essentially no practice with the experimental processor prior to data collection. Listeners scored the highest with their original processor. Little difference in speech understanding was observed for listener scores with processors using different stimulation rates. Speech recognition was significantly poorer only at the lowest stimulation rate and at high rates that used noninterleaved pulses. Speech recognition was similar for processors using 8, 12 or 16 electrodes. Only 4-electrode processors produced a significantly poorer performance. These results suggest that patients with present commercial implants are not able to make full use of the number of channels of spectral information delivered by the present speech processors. In addition, the results show no significant change in performance as a function of stimulation rate, suggesting that high stimulation rates do not result in improved access to temporal cues in speech, at least under quiet listening conditions.

Cochlear implant surgery significantly improves health-related quality of life as categorically stratified by the SF-36 questionnaire. These improvements were most evident in the mental health, emotional and social functioning, and physical functioning at work questions of the survey. Cochlear implant recipients younger than 65 years perceive a greater improvement in their level of energy, mental health, and social function compared with those older than 65 years.

Patients with MD who have bilateral severe to profound sensorineural hearing loss benefit significantly from CI. Ongoing dizziness in some patients with MD may result in quality of life improvements that are slightly less than seen for the average adult patient with CI. Larger studies are needed to corroborate the results.