In the normal auditory system, the perceived pitch of a tone is closely linked to the cochlear place of vibration. It has generally been assumed that highrate electrical stimulation by a cochlear implant electrode also evokes a pitch sensation corresponding to the electrode_s cochlear place (Bplaceĉ ode) and stimulation rate (Btemporal^code). However, other factors may affect electric pitch sensation, such as a substantial loss of nearby nerve fibers or even higher-level perceptual changes due to experience. The goals of this study were to measure electric pitch sensations in hybrid (short-electrode) cochlear implant patients and to examine which factors might contribute to the perceived pitch. To look at effects of experience, electric pitch sensations were compared with acoustic tone references presented to the non-implanted ear at various stages of implant use, ranging from hookup to 5 years. Here, we show that electric pitch perception often shifts in frequency, sometimes by as much as two octaves, during the first few years of implant use. Additional pitch measurements in more recently implanted patients at shorter time intervals up to 1 year of implant use suggest two likely contributions to these observed pitch shifts: intersession variability (up to one octave) and slow, systematic changes over time. We also found that the early pitch sensations for a constant electrode location can vary greatly across subjects and that these variations are strongly correlated with speech reception performance. Specifically, patients with an early low-pitch sensation tend to perform poorly with the implant compared to those with an early high-pitch sensation, which may be linked to less nerve survival in the basal end of the cochlea in the low-pitch patients. In contrast, late pitch sensations show no correlation with speech perception. These results together suggest that early pitch sensations may more closely reflect peripheral innervation patterns, while later pitch sensations may reflect higher-level, experience-dependent changes. These pitch shifts over time not only raise questions for strict place-based theories of pitch perception, but also imply that experience may have a greater influence on cochlear implant perception than previously thought.

Objectives-The purpose of this study was to determine if changes in the position of the stimulating electrode in the cochlea could be used to elicit the electrically evoked auditory change complex (EACC) from Nucleus cochlear implant users.Design-Nine postlingually deafened adults participated in this study. Each study participant had been using his or her Nucleus CI24 cochlear implant for at least 3 months prior to testing. The speech processor was bypassed and the output of the implanted receiver/stimulator was controlled directly. The stimulus was a 600 ms burst of a biphasic pulse train (1000 pps). In control conditions, the stimulating electrode was held constant and stimulation continued throughout the 600 ms recording interval. In experimental conditions, the EACC was elicited by introducing a change in the stimulating electrode 300 ms after the onset of the pulse train. The EACC was recorded using surface electrodes. Three recordings of 100 sweeps each were obtained for each stimulus condition. Bandpass filtering (1 -100 Hz) was used to minimize contamination of the recordings by stimulus artifact. Averaged responses were then smoothed using a 40 ms wide boxcar filter and standard peak picking procedures were used to analyze these responses in the time domain.Results-In each case, a clear onset response (P1-N1-P2) was recorded. In the experimental conditions, a second evoked potential, the EACC, was also recorded following the change in stimulating electrode. This second response had general morphologic characteristics that were very similar to those of the onset response. Increasing the separation between the two stimulating electrodes in the experimental conditions resulted in a general trend toward increased EACC amplitudes.Conclusions-This report describes results of a set of experiments in which the speech processor of the cochlear implant was bypassed and the EACC was recorded in response to a change in stimulating electrode position. EACC amplitude was shown to increase as the separation between the two stimulating electrodes increased. While preliminary in nature, these results demonstrate the Correspondence: Carolyn J. Brown, PhD, 127B SHC, Dept. Speech Pathology and Audiology, University of Iowa, Iowa City, IA 52242, Phone: 319-335-8734, Fax: 319-335-8851, Email: carolyn-brown@uiowa.edu. Reprints: Use address listed above for correspondence Electrically evoked, auditory potentials were measured from Nucleus cochlear implant users. The speech processor was bypassed and the implanted electronics were controlled directly. A 600 ms train of biphasic current pulses was presented. In experimental conditions, the stimulus train included a change in the stimulating electrode position. The amplitude of the responses that were elicited by this change in electrode location tended to increase as the distance between the two stimulating electrodes increased. These results suggest that it may be feasible to use electrophysiologic techniques to assess sensitivity to change in various aspects of an ong...

Consonant recognition was measured as a function of the number of stimulation channels for Hybrid short-electrode cochlear implant (CI) users, long-electrode CI users, and normal-hearing (NH) listeners in quiet and background noise. Short-electrode CI subjects were tested with 1-6 channels allocated to a frequency range of 1063-7938 Hz. Long-electrode CI subjects were tested with 1-6, 8, or 22 channels allocated to 188-7938 Hz, or 1-6 or 15 channels from the basal 15 electrodes allocated to 1063-7938 Hz. NH listeners were tested with simulations of each CI group/condition. Despite differences in intracochlear electrode spacing for equivalent channel conditions, all CI subject groups performed similarly at each channel condition and improved up to at least four channels in quiet and noise. All CI subject groups underperformed relative to NH subjects. These preliminary findings suggest that the limited channel benefit seen for CI users may not be due solely to increases in channel interactions as a function of electrode density. Other factors such as pre-operative patient history, location of stimulation in the base versus apex, or a limit on the number of electric channels that can be processed cognitively, may also interact with the effects of electrode contact spacing along the cochlea.

No abstract