Changes in Pitch with a Cochlear Implant Over Time

Abstract

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.

Integration of acoustic and electrical hearing

“…The present study extends these demonstrations of "auditory plasticity" in adult patients to the extreme case, where part of the speech spectrum, the low-frequency acoustic portion, is presented to the "normal" place along the cochlea and the electrically presented speech is shifted (and even severely compressed) to a much more basal location than normal. These findings are also in line with the observations of Reiss et al that the sensations of pitch can change over time in these patients, perhaps driven by the new place-frequency mapping of electrical stimulation [27]. This flexibility of the auditory system to integrate acoustic and electrical information under conditions of distortion and shifting certainly contributes to the success of the Iowa/ Nucleus Hybrid device.…”

“…Recent work from our laboratory has also shown that the pitch sensation associated with a particular Iowa/Nucleus Hybrid electrode can shift over time and that this pitch sensation appears to "migrate" toward the frequencies assigned to that electrode by the patient's everyday listening MAP (a cochlear implant speech processor map that assigns speech frequencies to particular electrodes) [27]. In this experiment, we look more closely at the possible effects of assigning "shifted-fromnormal" speech frequencies to the electrodes of the Iowa/ Nucleus Hybrid implant.…”

Strategies to Improve Music Perception in Cochlear Implantees

“…The insignificant effect of pitch-interval size on the differentiation tasks in the present study could be ascribed partly to the channel-setting of sound frequency and/or tone perception changes caused by cochlear implants (Nardo et al, 2007;Reiss et al, 2007).…”

Combined acoustic and electric hearing: Preserving residual acoustic hearing

“…Although patient selection criteria are different between the two groups (with Hybrid patients having more residual hearing), it is still quite interesting to see that very high recognition scores are possible even with a short (10mm insertion, 6 channels in the distal 6 mm) electrode. Reiss et al (2007b) hypothesize that these patients are capable of learning a highly compressed and shifted frequency map over time and that this may correspond to a perceptual change over time in the pitch sensation associated with each electrode (Reiss et al, 2007a). Turner et al (2004) demonstrated, using simulated Hybrid processing of speech presented to normal-hearing subjects, that high-frequency electrical stimulation along with acoustic lowfrequency hearing (as compared to full speech range electric stimulation alone) had the potential to provide a significant advantage for understanding speech in background noise, particularly when the competing signal was other talkers.…”