Bilateral cochlear implantation and Phase-Lock Speech Coding (PLS), a pilot study

Cochlear implantation is the primary therapy for profound deafness. A cochlear
implant provides hearing by direct electrical stimulation of the auditory
nerve. The translation from the acoustic sound, recorded by the implant*s
microphone, to the electrical stimulus for the nerve is called the speech
coding strategy. Several studies indicate that bilateral cochlear implantation,
i.e. an implant in each ear, may provide significant advantages over
single-sided implantation. These advantages are (1) a better ability to
localize a sound source and (2) better speech understanding in listening
situations with multiple interfering sound sources. These advantages are
limited, presumably due to inherent limitations of the current speech coding
strategies.

The ENT clinic in Groningen has developed a new speech coding strategy:
phase-lock speech (PLS) coding. This strategy distinguishes from existing
strategies by the explicit coding of acoustic fine-structure. In normal hearing
subjects, the advantages of binaural hearing depend in part on neural coding of
acoustic fine-structure. It is hypothesized that PLS coding improves binaural
hearing advantages over existing speech coding strategies by specifically
coding the acoustic fine-structure. It is the primary goal of this project to
test this hypothesis.

This is an exploratory pilot study, in which the hypothesis is tested by
extensive binaural hearing tests.

Subjects receive a second cochlear implant.

Subjects will undergo a second cochlear implantant surgery, followed by
adjustment of the implant and hearing training. These procedures will be
identical to the first implantation and are part of the standard medical care.
Thus, subjects are familiar with the procedures. Surgical risks are identical
to those of the first implant: (1) peri- and post-surgical infection, (2)
dizziness and vertigo, (3) tinnitus, (4) loss of residual acoustic hearing
function, if existing. The loss of residual hearing is usually compensated for
by the cochlear implant. One month after surgery, the second implant will be
adjusted using standard audiological procedures and using a standard speech
coding strategy. After 3 and 6 months, the effect of bilateral implantation
with the standard strategy will be tested. Then, the PLS strategy will be
installed on the implant hardware. It*s effect will be tested immediately.
Next, after one, and three months, binaural hearing with the PLS strategy is
evaluated. Finally, subjects are re-adjusted to the standard strategy, which
will be evaluated again after 3 months. Each audiometric testing session will
last approximately 4 hours (including breaks).