Pitch perception is a fundamental component of how humans process sound. Individuals who
use cochlear implants (CIs), surgically implanted devices which are able to restore a
limited range of hearing, struggle with pitch perception for a variety of reasons.
Although CIs can often restore the ability to hear speech from a single talker in quiet,
perception of more complex auditory stimuli like music is severely limited. CI users
often report music as being difficult, even displeasing, to listen to. These experiences
can be immensely frustrating, especially for people who experience deafness later in life
and have built strong emotional attachments to music, such as musicians or audiophiles.
Cochlear implant programming (also called "mapping") is done using a set of
generally-accepted default settings without taking into account individual differences of
precisely where CI electrodes are physically located in the cochlea. For this reason, CI
users commonly experience a place-pitch mismatch between the stimulation by an electrode
in response to a given frequency and the actual frequency specified by the original
cochlear location. CI users vary widely in their ability to adapt to place-pitch
mismatch; some adapt completely, others partially, and others not at all. The length of
time in which an individual takes to adapt is also highly variable. Bilateral CI users
may have differing adaptation between ears, leading to distortion of sound localization
and speech in noise perception abilities.
Flat Panel Computed Tomography (FPCT) is an imaging technique that consistently produces
high quality images with identification of the delicate cochlear structures and the
cochlear implant (CI) electrode contacts. FPCT imaging of the cochlea, combined with 3D
curved multiplanar reconstruction (MPR) software, has been shown to yield reliable
cochlear duct length measurements. With these resources, measurements of cochlear length
and determination of intracochlear electrode location relative to standardized cochlear
landmarks can be produced. These data are then utilized to create individualized
frequency allocation tables relevant to the actual physical location of CI electrode
contacts.
In this study, FPCT imaging, 3D curved MPR, and applied mathematics are used to quantify
the difference between theoretical and actual electrode contact placement with respect to
pitch-place mapping. Previous results have revealed significant deviations between
predicted and programmed characteristic frequencies, which are relevant for accurate
speech, pitch, and music perception. The goal of the study is to gather FPCT scans on a
cohort of 20 new CI recipients, and characterize the impact of long-term (1 year)
personalized pitch-place maps on a battery of speech and music metrics. The performance
with the FPCT-based programs will then be compared to performance using the manufacturer
default settings.
The novel aspect of this study involves working with newly implanted CI recipients and
programming these patients with custom CT-based programs. More specifically, CT-based
programs will be given to new CI recipients before any acclimation or programming of
clinical default maps occur. This differentiates the study from prior ones, as CT-based
programming has only been investigated in populations who have already used clinical
default maps for some substantial period of time (e.g. for 3 months, 5 years, etc.).
Participants will participate in a series of testing sessions to evaluate their speech
and music perception abilities over the course of the study. At the end of the study,
participants will be allowed to keep their preferred listening programs (i.e.,
experimental and/or default program).
The researcher team hypothesizes that bypassing the use of a clinical-based map is
imperative to fully understanding the effects of CT-based programming, as those who have
already used clinical default programs demonstrate much higher degrees of place-pitch
mismatch at baseline. By providing a new CI recipient with a custom CT-based program on
their very first day of electrical hearing (CI activation), there is a unique and novel
opportunity to minimize pitch-place mismatch from the outset, and to bypass the period of
time that the vast majority of CI recipients have when first adapting to a clinical
default program.
