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.

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.

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 (EAS). 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 non-implanted 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 (i) audiometric thresholds at ≤ 750 Hz, (ii) speech understanding scores (words in quiet and sentences in noise), and (iii) 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-moderate loss (r = −0.828) and within the group with severe-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.

ECoG thresholds may provide a useful metric for the assessment of residual hearing in cochlear implant subjects for whom it is not possible to perform behavioral audiometric testing.

PE stimulation can elicit pitch percepts lower than that of the most apical MP electrode; the PE pitch is lower by the equivalent of 0.5 to 2 MP electrodes.

Unbalanced bipolar stimulation, delivered using charge balanced pulses, was used to produce “Phantom stimulation”, stimulation beyond the most apical contact of a cochlear implant’s electrode array. The Phantom channel was allocated audio frequencies below 300Hz in a speech coding strategy, conveying energy some two octaves lower than the clinical strategy and hence delivering the fundamental frequency of speech and of many musical tones. A group of 12 Advanced Bionics cochlear implant recipients took part in a chronic study investigating the fitting of the Phantom strategy and speech and music perception when using Phantom. The evaluation of speech in noise was performed immediately after fitting Phantom for the first time (Session 1) and after one month of take-home experience (Session 2). A repeated measures of analysis of variance (ANOVA) within factors strategy (Clinical, Phantom) and interaction time (Session 1, Session 2) revealed a significant effect for the interaction time and strategy. Phantom obtained a significant improvement in speech intelligibility after one month of use. Furthermore, a trend towards a better performance with Phantom (48%) with respect to F120 (37%) after 1 month of use failed to reach significance after type 1 error correction. Questionnaire results show a preference for Phantom when listening to music, likely driven by an improved balance between high and low frequencies.

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Peripheral neural activation patterns suggest a similar spread of excitation for SI dual-electrode stimulation and the intermediate PE. The spread of excitation associated with sequential dual-electrode stimulation is generally different from the intermediate PE, and it varies depending on the order of the sequential pulses.