Simulating the effect of cochlear-implant electrode insertion depth on speech understanding

Dorman, Michael F.; Loizou, Philipos C.; Rainey, Dawne

doi:10.1121/1.420354

Cited by 168 publications

(166 citation statements)

References 6 publications

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“…Both hybrid and traditional implant patients note that speech through their implant initially sounds Bsqueaky^, but later sounds more normal and like regular speech [Dorman et al 1997;personal observations]. This again suggests that implant processors commonly assign speech frequencies to the wrong frequency-place locations, although the mismatch would be much smaller for traditional implant patients.…”

Section: Mechanisms Of Electric Pitch Shiftsmentioning

confidence: 99%

“…Correct allocation of acoustic frequencies to individual electrodes may be important for music and speech recognition (Dorman et al 1997;Fu and Shannon 1999a,b;Faulkner et al 2003;Baskent and Shannon 2004), although some studies suggest that implant users can adapt over time to spectrally shifted speech-frequency mappings (Rosen et al 1999;Fu et al 2005).…”

Section: Introductionmentioning

confidence: 99%

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Changes in Pitch with a Cochlear Implant Over Time

Reiss

Turner

Erenberg

et al. 2007

JARO

140

143

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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.

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Section: Mechanisms Of Electric Pitch Shiftsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Changes in Pitch with a Cochlear Implant Over Time

Reiss

Turner

Erenberg

et al. 2007

JARO

140

143

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“…A number of recent studies have been directed toward providing a better understanding of the role of electrode location and spacing on various perceptual attributes of hearing with a CI (Blamey et al 1996;Ketten et al 1998;Pfingst et al 2001;Skinner et al 2002;Yukawa et al 2004;Baumann and Nobbe 2006;Boex et al 2006). Several psychophysical studies have shown that spectral distortions such as apical or basal shift (Dorman et al 1997;Fu and Shannon 1999), nonlinear warping (Shannon et al 1998), and compression or expansion of the applied frequency map Shannon 2003, 2004) decrease speech perception, thus suggesting that an optimum fit of the frequency map for a given electrode position may significantly improve the performance of the CI listener. Although some studies have shown that speech perception with a frequency-shifted implant map can substantially improve with auditory training and if the patient has more time to adapt to the map (Rosen et al 1999;Fu et al 2005), an initial optimum frequency fit may provide immediate benefit for implant recipients and a better basis for the subsequent adaptation that occurs in most CI users.…”

Section: Introductionmentioning

confidence: 99%

Frequency Map for the Human Cochlear Spiral Ganglion: Implications for Cochlear Implants

Stakhovskaya

Sridhar

Bonham

et al. 2007

JARO

348

357

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The goals of this study were to derive a frequencyposition function for the human cochlear spiral ganglion (SG) to correlate represented frequency along the organ of Corti (OC) to location along the SG, to determine the range of individual variability, and to calculate an Baverage^frequency map (based on the trajectories of the dendrites of the SG cells). For both OC and SG frequency maps, a potentially important limitation is that accurate estimates of cochlear place frequency based upon the Greenwood function require knowledge of the total OC or SG length, which cannot be determined in most temporal bone and imaging studies. Therefore, an additional goal of this study was to evaluate a simple metric, basal coil diameter that might be utilized to estimate OC and SG length. Cadaver cochleae (n = 9) were fixed G24 h postmortem, stained with osmium tetroxide, microdissected, decalcified briefly, embedded in epoxy resin, and examined in surface preparations. In digital images, the OC and SG were measured, and the radial nerve fiber trajectories were traced to define a series of frequency-matched coordinates along the two structures. Images of the cochlear turns were reconstructed and measurements of basal turn diameter were made and correlated with OC and SG measurements. The data obtained provide a mathematical function for relating represented frequency along the OC to that of the SG.Results showed that whereas the distance along the OC that corresponds to a critical bandwidth is assumed to be constant throughout the cochlea, estimated critical band distance in the SG varies significantly along the spiral. Additional findings suggest that measurements of basal coil diameter in preoperative images may allow prediction of OC/SG length and estimation of the insertion depth required to reach specific angles of rotation and frequencies. Results also indicate that OC and SG percentage length expressed as a function of rotation angle from the round window is fairly constant across subjects. The implications of these findings for the design and surgical insertion of cochlear implants are discussed.

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“…formants, will be misrepresented. A misrepresentation of frequency, depending on severity, should cause (1) difficulties in adapting to electrical stimulation, (2) a low asymptote for performance, or (3) both (see, for example, Skinner et al 1995;Dorman et al 1997;Fu and Shannon 1999a, b;Fu et al 2002;Dorman and Ketten 2003;Rosen et al 1999).…”

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confidence: 99%

An Electric Frequency-to-place Map for a Cochlear Implant Patient with Hearing in the Nonimplanted Ear

Dorman

Spahr

Gifford

et al. 2007

JARO

Self Cite

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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.

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Simulating the effect of cochlear-implant electrode insertion depth on speech understanding

Cited by 168 publications

References 6 publications

Changes in Pitch with a Cochlear Implant Over Time

Changes in Pitch with a Cochlear Implant Over Time

Frequency Map for the Human Cochlear Spiral Ganglion: Implications for Cochlear Implants

An Electric Frequency-to-place Map for a Cochlear Implant Patient with Hearing in the Nonimplanted Ear

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