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J Am Acad Audiol 15:133–151 (2004)

Central Deafness Associated with a
Midbrain Lesion
Frank E. Musiek*
Lori Charette†
Diantha Morse‡
Jane A. Baran§

Abstract
Central deafness has been linked historically to bihemispheric involvement of
the temporal lobe, with more recent findings suggesting that compromise of
other cortical and subcortical structures can also result in this disorder. The
present investigation extends our understanding of the potential anatomical
correlates to central deafness by demonstrating that bilateral involvement of
an auditory structure within the midbrain can additionally result in this condition. Our subject was a 21-year-old male with a subarachnoid bleed affecting
both inferior colliculi. Significant auditory deficits were noted for the middle
and late auditory evoked potentials, while electrophysiologic measures of the
periphery indicated normal function. The patient was enrolled in a rehabilitation program for approximately 14 weeks. Although initially unresponsive to
sounds, the patient regained most of his auditory abilities during the 10 months
he was followed. This case documents the range of auditory deficits that may
be associated with damage to the inferior colliculi, and it profiles a hierarchical recovery of auditory function consistent with test findings.
Key Words: Auditory evoked potentials, auditory processing disorder, central auditory disorders, central deafness, inferior colliculus
Abbreviations: ABR = auditory brainstem response; ALD = assistive listening device; CT = computerized tomography; DL = difference limen; DPOAE =
distortion product otoacoustic emissions; MLR = middle latency response;
MRI = magnetic resonance imaging
Sumario
La sordera central ha sido históricamente relacionada con el compromiso bihemisférico del lóbulo temporal, aunque hallazgos más recientes sugieren
también que el compromiso adicional de otras estructuras corticales y subcorticales pueden producir este trastorno. La presente investigación amplia
nuestro conocimiento sobre la correlación anatómica potencial en la sordera
central, demostrando que el compromiso bilateral de una estructura auditiva
dentro del mesencéfalo puede también resultar en esta condición. Nuestro
sujeto fue un hombre de 21 años de edad con un sangrado sub-aracnoideo
que afectó ambos colículos inferiores. Una deficiencia auditiva significativa
fue notada en los potenciales evocados auditivos tardíos y de latencia media,
mientras las mediciones electrofisiológicas periféricas mostraron una función
normal. El paciente fue inscrito en un programa de rehabilitación durante 14
semanas. Aunque con una falta inicial de respuesta a sonidos, el paciente

†

*Department of Communication Sciences, Neuroaudiology Lab, University of Connecticut, Storrs, Connecticut; Gaylord
‡
§
Hospital, Wallingford, Connecticut; Meriden, Connecticut; Department of Communication Disorders, University of Massachusetts,
Amherst, Massachusetts
Reprint requests: Frank E. Musiek, Ph.D., Professor, Department of Communication Sciences, 850 Bolton Road, Unit 1085,
Storrs, CT 06269-1085; Phone: 860-486-3166; E-mail: frank.musiek@uconn.edu

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Journal of the American Academy of Audiology/Volume 15, Number 2, 2004

recuperó la mayor parte de sus capacidades auditivas a lo largo de 10 meses
de seguimiento. Este caso documenta el rango de deficiencias auditivas que
pueden asociarse con una lesión en los colículos inferiores, y brinda un perfil
jerárquico de recuperación de la función auditiva, consistente con los hallazgos en las evaluaciones.

Palabras Clave: Potenciales evocados auditivos, trastorno de procesamiento
auditivo, trastornos auditivos centrales, sordera central, colículo inferior

Abreviaturas: ABR = respuestas auditivas del tallo cerebral; ALD = dispositivo de ayuda auditiva; CT = tomografía computarizada; DL = umbral diferencial;
DPOAE = emisiones otoacústicas por productos de distorsión; MLR = respuestas de latencia media; MRI = imágenes por resonancia magnética

C

entral deafness is a relatively rare
disorder but one that, if appropriately
defined and investigated, can add
much to our understanding of the specific
anatomical structures within the human
brain that are involved in the processing of
auditory stimuli. Much of what is currently
known about the functioning of the central
auditory nervous system (CANS) has been
gleaned from studies of patients with
documented lesions of the brain (Damasio
and Damasio, 1989). Investigations that
correlate specific auditory deficits with known
lesion sites serve to establish clear links
between auditory functions and their
anatomical correlates. Although significant
advances have been made on this front, the
exact structures that compromise the CANS
in humans have not been completely
delineated. This is particularly true of the
cortical and subcortical structures that
support hearing. Additional studies of
patients with CANS damage are needed to
build upon the existing knowledge base that
details the neural substrate involved in
hearing and hearing disorders, and patients
with central deafness provide unique
opportunities to add to this knowledge base.
Individuals with central deafness often
present with a rather dramatic auditory
deficit that is not commonly observed in other

134

patients with CANS compromise. Most
notably, these patients often demonstrate
inconsistent or no responses to sound (Hood
et al, 1994; Musiek et al, 1994; Murray and
Fields, 2001). Upon initial assessment, these
patients may appear to have a peripheral
hearing loss since pure-tone testing typically
reveals a severe to profound hearing loss—
a finding more commonly associated with
compromise of the peripheral hearing system.
However, if objective test measures of
peripheral function are administered,
compromise of the periphery is often ruled
out, and central auditory system involvement
is suggested. With additional testing (e.g.,
middle and late auditory evoked potentials),
the CANS involvement can be documented.
Unfortunately, if such testing is not
undertaken, then the central origin of the
hearing loss is likely to remain unidentified.
To date there have been a number of
case studies reported in the literature that
have clearly implicated bihemispheric
involvement of Heschl’s gyrus as the likely
origin of the auditory deficits noted in many
patients with central deafness (see Musiek
and Lee, 1998). In their review of 33 cases of
patients with central deafness, Musiek and
Lee (1998) found that bihemispheric
involvement of the temporal lobe was a
common finding in most of these cases. This

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observation lends some support to the
commonly held notion that damage to the
primary auditory areas (i.e., Heschl’s gyrus)
of both hemispheres must be present in order
for the auditory deficits typically associated
with this condition to be present. Although
bihemispheric temporal lobe compromise was
a common finding in the cases reviewed by
Musiek and Lee, this site of lesion was not
reported for all of the cases reviewed. Thus,
the possibility of other lesion sites must be
entertained. In addition, their review of the
lesion sites for the 33 patients included in
their analysis indicated that multiple sites of
lesion were involved in nearly every case,
with other lesion sites including subcortical
structures, the parietal lobe, the frontal lobe,
the basal ganglion, the medial geniculate
body, and even the pons. With multiple sites
of lesions, it is difficult to determine which
site, or combination of sites, may have
contributed to the central deafness.
One of the challenges in considering the
available data on cases with central deafness
is lack of consistency in the terminology used.
Investigators have used a number of terms
to describe their patients, including “central
deafness,” “cortical deafness,” “auditory
agnosia,” and “word deafness,” and in many
cases the use of these terms have not been
defined fully. For example, “word deafness”
has been used to describe a condition wherein
patients are unable to recognize words, but
the ability to perceive other auditory abilities
is not necessarily addressed, leaving the
reader uncertain as to the status of this
auditory skill in many of the patients studied.
On the other hand, “central deafness” has
been used to describe patients with a variety
of symptoms and test findings, including
those that demonstrate a complete lack of
response to sounds of any type (including
speech), as well as others who show some
reductions in hearing sensitivity (hence, not
deaf in a strict interpretation), but who show
inordinately poor speech recognition abilities
or other auditory processing abilities that
cannot be accounted for solely on the basis of
the noted reduction of hearing sensitivity.
For our purpose we have chosen to use
the term “central deafness” to refer to a
condition in which the following
characteristics are noted: (1) pure-tone
thresholds may be absent or they may show
severe decrements in hearing sensitivity that
do not have an origin in the peripheral

hearing system (this may change over time);
(2) speech intelligibility is likely to be severely
affected by the apparent compromise of
hearing sensitivity, and the extent of the
speech recognition deficit may be more severe
than would have been predicted based upon
a consideration of the pure-tone thresholds;
(3) objective measures of peripheral and
brainstem functions are normal unless the
brainstem is involved and contributing to
the central deficit; and (4) evoked potentials
that assess electrophysiological responses
that originate in the cortex or the radiations
to the auditory cortex show abnormalities.
As alluded to above, the current lack of
specification of the anatomy of central
deafness can be attributed to a number of
factors. These include the following factors:
(1) lesions are seldom specific to structures
of interest, (2) radiological evidence in the
past has not been exact enough to define the
boundaries of damage in auditory system,
(3) semantic differences in the terminology
used to describe central deafness have
precluded precise comparison of the data
since it is difficult to define the patient
populations in many cases, and (4) the use of
limited audiologic testing in many
investigations may have resulted in less than
a complete elucidation of the nature and the
full extent of the auditory deficits in many of
the patients studied. Fortunately, recent
advances in radiological imaging techniques
now permit more careful specification of the
location and precise boundaries of lesions
within the CANS, and developments in the
area of electrophysiologic assessments have
contributed to the ability of the audiologist
to document auditory deficits arising from
cortical and subcortical structures.
A careful review of anatomy of central
auditory deafness based upon the available
(but qualified) empirical and hypothetical
data would argue against the primary
auditory areas as being the only auditory
regions that could precipitate central auditory
deafness (see Musiek and Lee, 1998; Samson
et al, 2001). Other cases, with little or no
documented involvement of the temporal
lobes, have shown that central deafness can
result from compromise associated with
bilateral infarcts of the insula (Habib et al,
1995), bleeds of the putamen (Nishioka et al,
1993; Makino et al, 1998; Wakabayshi et al,
1999; Taniwaki et al, 2000), third ventricle
hydrocephalus affecting the thalamocortical

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Journal of the American Academy of Audiology/Volume 15, Number 2, 2004

pathways (Shivashankar et al, 2001),
bilateral medial geniculate body involvement
associated with a tentorial meningioma
(Karibe et al, 2000), arteriovenous
malformation embolization involving the
inferior colliculi (Vitte et al, 2002), and inferior
colliculi destruction and medical geniculate
body degeneration associated with a pineal
body tumor (Masuda et al, 2000). The present
case adds to the growing body of evidence that
indicates that compromise of auditory
structures outside of the primary cortical
areas can result in central deafness.
CASE REPORT

History
This is a report of a 21-year-old college
student, who had been in good health with no
problems in hearing prior to the time of the
medical condition that is described below.
He was sent from the college to a local
hospital because of severe headaches and
vomiting. During his short stay at the local
hospital, he became unresponsive and was
transferred to a large tertiary care hospital.
At the second hospital, he became somewhat
more responsive, but he was combative and
nonverbal. Key observations at this time
included unequal and minimally responsive
pupils and purposeful movements to noxious
stimuli; however, the patient did not follow
commands and was totally unresponsive to
verbal stimuli. A computerized tomography
(CT) scan at this time showed a subarachnoid
bleed. Soon after admission, a diagnosis of
Neisseria meningitis was rendered. This rare
type of meningitis, to our understanding, can
result in accompanying vascular lesions.
During the first two weeks following his
medical incident, the patient improved on
most fronts. He started vocalizing and saying
a few words, which were used appropriately
the majority of the time. He was able to move
all extremities appropriately and
purposefully, and his mental status was
improving. He communicated by writing on
a pad, which he did reasonably well; however,
he remained unresponsive to all sounds. He
was soon transferred to a rehabilitation
hospital and shortly after the transfer became
an outpatient. As an outpatient, he was seen
over the next five months for audiological
follow-up and auditory therapy as his main

136

problem over this period of time was his
hearing loss.
From a medical standpoint, the patient
improved markedly over the first six weeks
of his outpatient treatment, and there were
no major concerns in this regard. However,
he continued to be seen for audiological followup following his discharge so that any
additional changes in his auditory function
could be monitored. His schedule of
audiological testing included a number of
evaluations that were completed over the
first two months immediately following his
medical incident, and then subsequent to
this he was seen only periodically. The data
reported in this study documents the results
of most of the formal audiological evaluations
that were completed over a 10-month period.
Because the patient became fatigued quickly,
especially during the initial six weeks, he
had to be brought back for repeated visits at
various times to complete his audiological
evaluations. In addition, the amount of time
available for testing was often limited due to
a variety of circumstances. Hence, the
timelines for testing are not quite as
congruent as we would have liked, nor are the
evaluations as extensive and complete in all
cases as would have been desired.
Magnetic Resonance Imaging (MRI)
At the beginning of his third week in the
hospital, an MRI was performed. The MRI
showed infarcts at the superior left
cerebellum/occipital lobe and the left inferior
temporal lobe. Neither of these regions is
considered “auditory.” However, in the
midbrain, both inferior colliculi were almost
totally infarcted with some spread of the
compromise into the inferior aspect of the
superior colliculi (see Figures 1a, 1b, and
1c). A more specific radiologic interpretation
indicated that perhaps there was less
involvement in the anterior or ventral aspects
of the colliculi than in the posterior aspect of
the colliculi.
Informal Observations on Hearing
As mentioned earlier, hospital personnel
working with this young man noted no
response to any sound on the part of this
patient for the best part of the first week of
his hospitalization. Commencing toward the
end of the first week of his hospital stay, and

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Figure 1. Top: a transverse MRI view showing the
involvement of both inferior colliculi (arrows), as
well as the left lateral aspect of the cerebellum. It
appears that there may be slightly greater area
involvement for the right inferior colliculus compared to the left. Middle: a mid saggital MRI showing the involvement of the inferior colliculus (arrow).
Bottom: a human brain specimen that emphasizes
a posterior view of the pons, midbrain, and thalamus.
The area inside the dashed box reflects the authors’
interpretation of the involved anatomy in this study’s
subject. The region of involvement encompasses both
inferior colliculi and the inferior fringe of the superior colliculi. Key: 1 = inferior colliculus, 2 = superior
colliculus, 3 = brachium of the inferior colliculus, 4
= medial geniculate bodies, 5 = fourth ventricle, 6 =
cochlear nucleus area. Courtesy of W. T. Mosenthal
and F. E. Musiek.

continuing for several weeks thereafter, the
patient claimed he heard a certain sound,
yet other people in the room with him did not
hear the sound. Beginning in his second
week, the patient acknowledged hearing some
sounds in his environment that were actually
present, but he could not identify the exact
nature and/or the source of these sounds. It
appeared that the sounds that were heard
were relatively loud and of a broad spectrum.
By the third week of his hospital stay, definite
improvements in hearing were noted. The
patient could hear voices, but he could not
understand anything that was being said to
him. He stated that “voices don’t [didn’t]
sound like voices.” He was speaking often, but
hospital personnel noticed that his voice was
monotone. Listening was a strain, and it
fatigued him to the point where he often
complained about it. He continued to hear
environmental sounds, such as a dish being
dropped and water running from a faucet, and
he seemed to be able to discern loud sounds
from soft sounds. However, he continued to
be inconsistent in his identification of the
source(s) of environmental sounds. The
patient additionally complained of extreme
difficulty listening to people speak whenever
background noises were present. At this point
in his recovery, he was able to read slowly, and
this skill has continued to improve over time.
In the fourth week post–medical incident,
the patient reported that he felt his hearing
was improving. He could hear voices on TV
but could not understand what was being
said. In general, the patient knew when
people were speaking but could not follow
speech on a consistent basis. He stated that
riding in a car was a difficult situation
because everything was too loud. He was
identifying more environmental sounds and
was encouraged when he identified the
clicking of high heels caused by someone
walking on a hard floor. There remained
some disassociation between what the patient
believed he heard and what sounds were
actually present in his environment. He
claimed to be able to hear women’s voices
better than men’s, and he reported that he
could hear parts of his girlfriend’s voice on the
phone. During this time period, the patient
began to experience bilateral tinnitus (ringing
type sound), which he reported was worse in
the morning than later in the day.
In the time period from about 5 through
12 weeks, the patient’s hearing continued to

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Journal of the American Academy of Audiology/Volume 15, Number 2, 2004

show steady improvement. He could now
understand several words, and this ability
gradually improved over time but was highly
dependent on the patient’s being located in
a quiet environment. Background noise, even
if of a low intensity (e.g., noise generated by
a small fan), caused considerable problems in
his understanding of speech. He noted that
he heard better when he was actively
participating in a conversation compared to
when he was listening passively. He reported
that speech seemed muffled and described his
listening experiences as if he were listening
to speech over a two-way radio transmitter.
He could hear birds chirp but described the
chirping of the birds as having a “robotic”
quality. His therapist noted that his voice
was softer at this time, and possibly less
monotone.
In the post–hospital admission period
from 12 weeks to 10 months, the patient was
seen only a few times formally. His ability to
understand speech in quiet continued to
improve, and he was able to follow most
conversations. Complex and similar sounding
words remained difficult for him to correctly
interpret and discriminate, and background
noise continued to be a major detriment to his
accurate understanding of speech. The
patient’s confidence in communication
improved considerably over this period of
time, and at this point in his recovery he
had gone back to college and appeared to be
doing
satisfactorily
with
some
accommodations such as preferential seating.
As part of his rehabilitation program, the
patient had been provided an assistive
listening device (ALD), which provided some
assistance; however, there was some
reluctance on the part of the patient to use
it consistently as he did not want to become
dependent upon the device. The patient was
motivated to act as if he has no problem at
all and therefore downplayed use of the ALD,
as well as some of the academic
accommodations that were recommended.
His auditory behavior at 10 months after his
medical incident was similar to that of an
individual with a moderately severe highfrequency hearing loss. However, background
noise continued to be a major problem, more
so than would be expected for a person with
only a moderately severe high-frequency
sensorineural hearing loss.

138

PROCEDURES

Pure-Tone and Speech Audiometry
All audiological tests were conducted in
sound-treated rooms. Conventional pure-tone
air- and bone-conduction threshold techniques
were used to establish hearing thresholds
for this patient; however, at times these had
to be modified to accommodate the patient’s
needs. Spondee thresholds were obtained on
some occasions using only a small subset of
spondees as indicated in the test results
section. Speech recognition measures were
conducted using the Northwestern University
Test Number Six (NU-6). Speech audiometry
was carried out using monitored live voice
procedures as this mode of presentation
seemed most clinically feasible particularly
during the early evaluations of the patient’s
hearing.
Immittance Audiometry
Tympanograms and acoustic reflexes
were derived in a conventional manner using
a GSI 1733 middle-ear analyzer. Acoustic
reflexes were measured both ipsilaterally
and contralaterally at 500, 1000, and 2000 Hz.
Otoacoustic Emissions
Distortion product otoacoustic emissions
(DPOAEs) were derived for this patient.
Levels (L1, L2) were 65 dB SPL and 55 dB
SPL, and the f1 to f2 ratio was 1.2. The left
ear DPOAEs were measured for frequencies
from 600 to 8000 Hz, and the right ear for
frequencies from 800 to 8000 Hz (the lower
frequencies could not be measured in the
right ear due to the presence of excessive
noise at these frequencies). Four distortion
products per octave were obtained for each ear
(see Smurzynski, 1994 for details of this
procedure).
Auditory Brainstem Response (ABR)
All ABR testing was conducted using 100
µsec clicks presented through TDH-39
earphones to each ear independently at 85 dB
nHL at a rate of 15.7 clicks per second unless
otherwise noted. Neuroelectrical activity was
recorded from electrodes attached to the high
forehead and each earlobe (one reference and

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one ground) and averaged over 2000 trials.
Impedance across the electrodes was
maintained at less than 5 kohm. Filter bands
for the ABR were set at 150 to 3000 Hz with
a 12 dB per octave roll-off. Responses were
analyzed over a 10 msec time period.
Middle Latency Evoked Response
(MLR)
The MLR was obtained using 100 µsec
clicks presented through TDH-39 earphones
at 70 dB nHL at a rate of 8.7 clicks per second
for each ear. For the initial test session,
electrodes were placed at Cz and referred to
either A1 and A2; however, all subsequent
MLR recordings were conducted with
electrodes at Cz, C5, and C6 with the same
references. Impedance across the electrode
array was maintained at less than 5 kohm.
In all cases the reference electrode was on the
side of the head that was receiving the click
stimulus. There were 800 accepted trials
conducted for each run, and filtering was 20
to 1500 Hz with a 12 dB per octave roll-off.
The time period for analysis was 70 msec.
P300 Potential
The P300 was conducted in each ear
using an odd-ball paradigm with 1000 Hz
and 2000 Hz tones representing the frequent
and rare stimuli, respectively. These tones
had a 10 msec rise and fall time and a 20 msec
plateau and were presented at 70 dB nHL
through TDH-39 earphones at a rate of 1.2
stimuli per second. Electrical activity from the
scalp was picked up by electrodes placed at
Fz, Cz, and Pz. Stimuli presentation rates
were set at 80% for the frequent stimulus and
20% for the rare stimulus, and the total
number of stimuli to be accepted during each
run was fixed at 300. Impedance across
electrodes was less than 5 kohm. Filtering
was set at 1 to 30 Hz with a 12 dB per octave
roll-off. The time window was 800 msec. The
patient had to count the number of rare
stimuli and report this number at the end of
each run (a score of >80% correct behavioral
counting performance was required for the
acceptance of an electrophysiological
response). Responses from the rare and
frequent stimuli were averaged separately.
The frequent stimuli yielded late potentials
N1 and P2, and the rare stimuli provided
N1, P2, and P300 waves for analysis.

Intensity Discrimination
Intensity discrimination testing was
conducted in each ear for three frequencies
(500, 1000, and 2000 Hz). Each test stimuli
consisted of the presentation of two tones
that were delivered at either the same
intensity level or at different intensity levels,
and the patient was asked to indicate if the
tones were the same or different in loudness.
Each tone was 500 msec tones in duration
with a 40 msec rise-fall time, and the
interstimulus interval between the two
successive tones was approximately 1 sec in
duration. Trials of equal versus different
intensities were presented at random. The
reference presentation level was fixed at 50
dB HL; thus, in each test stimuli, one of the
tones was presented at this intensity level
while the second tone was varied for the
purpose of identifying the smallest intensity
difference that the patient could recognize.
The patient was required to achieve two out
of three correct judgments at a particular
intensity difference before going further. This
procedure was repeated several times, and
the average of difference limens (DLs)
obtained was computed. At times this
procedure had to be modified to accommodate
the patient. For example, on some days, more
practice items with large DLs were provided
and/or the presentation approach was slightly
changed to allow a better orientation toward
the test.
TEST RESULTS

Basic Audiological Evaluation
The first formal audiological evaluation
was performed about two and one-half weeks
after admission. At this point, the patient’s
hearing had already improved considerably
from the first week; however, in spite of this
noted improvement in hearing, pure-tone
thresholds were difficult to obtain, especially
at the low frequencies with a frequent
occurrence of false positives. This difficulty
with the assessment of pure-tone sensitivity
continued for most of the early evaluations,
and to a lesser degree for later evaluations.
One of the factors that contributed to the
difficulty with determining thresholds for
pure tones was that the patient noted little
or no tonality in the stimuli; hence, the sounds

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Journal of the American Academy of Audiology/Volume 15, Number 2, 2004

Figure 2. The initial audiogram and acoustic reflex
test results for a 21-year-old male with bilateral
involvement of the inferior colliculi. Spondee thresholds and speech recognition could not be tested (CNT)
for either ear (AU) at this time. Key: X, O = left and
right ears, [ ] = bone conduction right and left sides,
DNT = did not test, AU = both left and right ears, CNT
= could not test, bone conduction was not tested at
250 Hz.

were not distinctive. This was particularly
problematic during the first few evaluations,
especially for low frequencies and the right
ear. Another factor that was likely to have
affected his performance during this initial
evaluation, as well as in other subsequent
evaluations, was the difficultly that the
patient reported in maintaining his attention.
At the time of his initial evaluation, a severe
low-frequency sensorineural loss, rising to a
mild to moderate loss, was indicated
bilaterally (Figure 2). Speech audiometry
could not be obtained during this evaluation
for either ear, but tympanograms were of
normal pressure, compliance, and shape
bilaterally. Ipsilateral and contralateral
acoustic reflex thresholds were grossly within
the normal range for absolute threshold
levels for both ears, but these thresholds
were at reduced sensation levels in reference
to pure-tone thresholds for both ears at 500,
1000, and 2000 Hz.

140

Figure 3. An audiogram showing pure-tone thresholds, spondee thresholds for selected spondees, speech
recognition scores, and acoustic reflex findings. These
results were obtained at approximately three and onehalf weeks following the patient’s hospitalization.

The next formal evaluation was
performed at three and one-half weeks. As can
be seen in Figure 3, there was a definite
improvement in the hearing thresholds for
both ears. Spondee thresholds were obtained
bilaterally for the first time using selected
spondees; however, these thresholds were
elevated and in poor agreement with the
pure-tone averages for both ears. Speech
recognition could not be tested at this time
as the patient could not understand even the
carrier phrase. Acoustic reflex and
tympanometric test results remained normal
bilaterally.
The next audiological assessment was
conducted at five weeks (Figure 4), and
although it showed improvement at the mid
and high frequencies, the low frequencies
were difficult to assess. There was so much
variability in performance at the low
frequencies for the right ear that thresholds
could not be established. The patient claimed
that the low-frequency tones (especially for
the right ear) “sounded like the wind blowing
tall grass in a field.” Speech recognition could

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Figure 4. An audiogram and speech recognition
results at five weeks. The “?*” indicates the “best
guess” thresholds for the right ear at these frequencies as threshold criteria could not be achieved at this
time due to variability in responses and fatigue on the
part of the patient.

Figure 5. An audiogram, spondee thresholds, and
speech recognition scores for each ear and in the binaural (Bin.) condition obtained at 10 weeks.

not be tested. The patient became very
fatigued during this evaluation, and his
motivation was dwindling.
The next audiogram was at 10 weeks
(Figure 5). Pure-tone thresholds had
improved to close to normal bilaterally at
this time and were in good agreement with
the spondee thresholds bilaterally. At this
evaluation, speech recognition could be tested
for both ears and in a binaural (diotic)
condition for which the best score was
obtained. At approximately five months,
speech recognition had improved into the
80% range bilaterally as informal
assessments during his rehabilitation period
were conducted. He was discharged from
therapy at five months. At 10 months he was
seen for assessment and showed essentially
a normal audiogram and speech testing
(Figure 6). As mentioned earlier, however,
he continued to experience difficulty with
background noise.
Otoacoustic Emissions
Figure 6. An audiogram at 10 months with spondee
thresholds and speech recognition scores.

Distortion product otoacoustic emissions
were administered approximately four weeks

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Journal of the American Academy of Audiology/Volume 15, Number 2, 2004

Figure 7. DPOAEs responses for the left and right ears. The heavy solid line is the patient’s DPOAE levels;
the thin solid line is the patient’s noise floor; the dashed line is the average noise floor; and the dotted line and
dashed/dotted lines are 10th and 90th percentiles.

after hospital admission. The left ear results
were essentially normal for absolute DPOAE
levels and DPOAE to noise floor
measurements for frequencies 600 through
6000 Hz (Figure 7), whereas the right ear
results were at normal absolute levels from
800 through 2000 Hz, but at abnormal levels
for the higher frequencies tested (Figure 7).
The right ear DPOAE to noise floor
measurements were grossly normal for all
test frequencies (800 through 6000 Hz). The
patient was anxious and tense during this
evaluation, and reliable measurements could
not be made below 800 Hz due to excess noise.

Middle Latency Response (MLR)
The initial MLR was conducted at three
and one-half weeks and showed no readable
response for either ear (Figure 9). A second
MLR derived one week later again revealed
no repeatable responses for either ear. The
first follow-up MLR that showed a notable
change was derived at 24 weeks (Figure 10).
At this time, a meager Pa wave began to
emerge at essentially normal latencies for
both ears across all electrode sites. It was
difficult to determine if an Na wave was
present at this time, but it seems doubtful.

Auditory Brainstem Response (ABR)
The initial ABR was performed at three
and one-half weeks and showed normal waves
I, II, and III bilaterally. It appeared that the
IV-V complex was compromised for both ears.
It is possible that wave IV could be normal,
but the amplitude and morphology of V is not
as would be expected for either ear (Musiek
and Lee, 1995). The amplitude of the IV-V
complex is less than half the amplitude of
wave I bilaterally. This abnormal V-I
amplitude ratio highlights the compromise of
the IV-V complex (Musiek and Lee, 1995). The
ABR was evaluated several times over the
recovery period up to 10 months but remained
essentially the same as shown in Figure 8.
Figure 8. The initial ABR.

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Figure 9. The initial MLR.

Figure 10. An MLR obtained at 24 weeks.

The Nb and Pb waves were absent. At 10
months, the MLR was more noisy but showed
similar responses to those noted at 24 weeks.

paradigm) showed no readable responses at
four weeks (Figure 11). An evaluation at 9
weeks showed a P300 emerging for both ears
across all electrode sites (Figure 12). The P300
was within the normal latency range for the left
ear stimulation but was extended for the right
ear stimulation. The P2 also began to emerge,
though attenuated, at Fz and Cz electrode
sites for both ears. The latency of P2 was
extended (240 msec), and an N1 was not seen
for any recording site at nine weeks. At 10
months, the P300 increased in amplitude and
decreased slightly in latency across the Pz and
Cz electrode sites for both ears. The N1 and P2
for both ears remained essentially the same for
Fz and Cz electrode sites; however, at 10
months a P2 emerged for the Pz electrode
position (Figure 13).

P300 Potentials
The P300 as well as the N1 and P2 late
potentials (as derived using an odd-ball

Intensity Discrimination

Figure 11. The initial findings for the P300 as well
as late auditory evoked potentials (N1 and P2).

Intensity discrimination was measured
at 5 and 11 weeks. As depicted in Figure 14,
there was considerable improvement in
intensity discrimination over this period of
time. The right ear, which was the ear with
poorer performance at five weeks, improved
more than the left ear. At five weeks, the
right ear could not be assessed due to too
great of a hearing loss. The patient performed
better in the binaural condition for both test
sessions (Figure 14). The cut-off for normal

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Journal of the American Academy of Audiology/Volume 15, Number 2, 2004

Right Ear

Left Ear

Figure 12. Left and right ear results for the P300 and late auditory evoked potentials at nine weeks.

performance on this task is 2 dB for both
monaural and binaural presentations.
REHABILITION PROGRAM

T

h e au r al r eh abilitati on p rogra m
commenced approximately one month
after hospital admission and continued on
a consistent basis for about four and onehalf months. Individual therapy sessions
were held once per week for one to one and
one-quarter hours, and the patient’s
performance on the various therapy tasks

Left Ear

outlined below was monitored throughout
this period. Task difficulty was governed to
be in the moderate range so that overall the
tasks were not too demanding or too easy
and the patient was either directly or
indirectly provided feedback as to his
performance during training procedures.
The p a t ient wa s a lso given t herap y
assignments to complete at home. These
includ ed such a ct ivit ies a s a ud it o r y
directives, discrimination tasks, and
critically listening to music. The description
of the formal therapy has been divided into

Right Ear

Figure 13. Left and right ear results for the P300 and late auditory evoked potentials at 10 months.

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Midtherapy Sessions (with and
without Visual Cues)

Figure 14. The intensity DL derived at 500, 1000, and
2000 Hz in each ear at 5 weeks and at 11 weeks. At
5 weeks the DL at 500 Hz could not be recorded for
the right ear.

three time periods; early (approximately
the first month), mid (approximately the
next two months), and late (approximately
the last month and a half).
Early Therapy Sessions (with Visual
Cues)
One of the first therapy goals was to
work on the patient’s vocal intonation as the
patient’s voice was monotone. Early therapy
activities additionally focused on having
the patient respond appropriately to
fundamental questions about himself.
Therapy on identifying and discriminating
speech and environmental sounds was a
major component of this therapy period.
The patient was asked to make judgments
as to intensity differences between and/or
among sounds both in formal and informal
paradigms. In addition there was some
work on speech reading and emphasizing
the use of visual cues. Much therapy was
centered around multimodality stimulation
and associating cues across different
modalities.

In this therapy period, the patient was
asked to identify familiar voices and to try to
discriminate male from female voices. Work
was continued on identifying and
discriminating environmental sounds that, for
the most part, were tape recordings that
provided a wide variety of acoustic stimuli.
Since the patient liked popular music, some
therapy procedures centered around
identifying songs and their artists. The
patient also spent time repeating sentences
that were presented to him in the presence
of background noise that was varied in
terms of noise type and level. Toward the
end of this therapy period, auditory training
consisted of identifying vowels, blends, and
consonants using Sloan’s (1986) materials.
Discriminating homophonous words and
contrasting nonsense words with real words
in both monaural and binaural listening
conditions was also conducted. The patient
was asked to read aloud and listen to himself,
and intensity discrimination tasks were
continued. Finally, a portion of the therapy
time was often devoted to work on one-, two-,
and three-step auditory directives.
Late Therapy Sessions (with and
without Visual Cues)
At this point, the patient had made
considerable improvement, and, accordingly,
the tasks were made more challenging.
Discrimination tasks with similar sounding
phonemes, consonant-vowels (CVs), vowelconsonants (VCs), and homophonous words
became a major focus in therapy.
Identification tasks involving the presentation
of words and sentences in noise were
continued, and the patient was also asked to
identify and correct words that were
purposely distorted in a sentence. The patient
claimed he had difficulty in group discussions
recognizing when he was being spoken to
and responding appropriately. He was
provided training on using visual cues in
these situations to help him determine when
he was expected to be part of the conversation.
An assistive listening device (ALD) was
introduced, and although the patient
experienced some success with this device, he
was not in favor of its long-term use. Shortly
after the formal therapy sessions ended, the

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Journal of the American Academy of Audiology/Volume 15, Number 2, 2004

patient went back to college with an ALD. He
was also provided a note taker for his classes.
DISCUSSION

C

ases of central deafness are indeed a
rarity. Usually most cases of central
deafness involve vascular damage to the
primary auditory area in both cortices
(Musiek and Lee, 1998). Even more unusual
is central deafness associated with lesions of
the brainstem or subcortex. Unlike the
majority of cases of central deafness that
result from bilateral auditory cortex lesions,
this case had healthy (auditory) cortical and
subcortical substrate. In this case, the
auditory deficits noted were most likely
related to impulse disruption arising at the
midbrain level, which deprived the cortex of
appropriate neural input from both sides of
the midbrain. This case is one that showed
recovery of many, but not all, higher-level
hearing processes. By following this patient
for 10 months, information as to the nature
of the recovery process was gained.
Informal and Formal Observations of
Hearing: Course of Recovery

We believe there is a strong possibility
that this patient may have been totally
centrally deaf during the first week to week
and a half post–admission to the hospital.
Hospital personnel reported that the patient
was unresponsive to acoustic stimuli during
this period of time. By the time the first
hearing test was completed at two and onehalf weeks, the patient had recovered
considerable hearing ability, but he remained
essentially word deaf throughout the first
month following his medical incident. Suffice
it to say, the involvement of the inferior
colliculi created a major deficit across all
aspects of hearing.
The informal observations of this
patient’s hearing recovery reflected a logical
progression, which began with the return of
the ability to perceive simple sounds and
increased to the perception of more complex
sounds (speech). Initially the patient could not
detect any sounds; however, within the first
week he could detect sounds but could not
identify them. The detection and subsequent
identification of simple environmental sounds
was followed by the recognition of more
complex and less familiar acoustic stimuli. By

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10 weeks post–hospital admission, the patient
could communicate reasonably well when
visual cues were optimized, and the acoustic
environment was ideal. The patient’s
improvement for hearing in poor acoustic
(noisy) environments was minimal in the
first few weeks after his medical incident, and
even at 10 months this continued to be a
major problem for this patient.
Formal audiological testing showed a
similar progression of recovery. The simplest
stimuli, pure tones, were the first to show
progress in the recovery process and ended
up in the normal range bilaterally. The
spondee thresholds eventually progressed to
within the normal range, as did speech
recognition ability although the latter did
require more time. The evoked potentials,
other than the ABR, showed improvement
over time. However, none of the evoked
potentials recovered to normal status. This
progression of regaining auditory perception
for simple and then more complex processes
is consistent with what has been reported
previously in the literature for patients
recovering from CANS damage (Mendez and
Geehan, 1988; Nishioka et al, 1993; Musiek
et al, 1994). The more complex the acoustic
stimulus, the more neural substrate is
needed. This has been well demonstrated in
dichotic listening paradigms in people with
temporal lobe damage (Kimura, 1961). In
cases of central deafness, neural damage is
extensive, and recovery of sufficient neural
substrate to support complex processing
requires an extended period of time (Mendez
and Geehan, 1988).
This case opposes the classic concept
that central auditory lesions do not affect
pure-tone thresholds. This case and other
studies on both humans and animals
demonstrate that central auditory
involvement can result in the reduction of
pure-tone sensitivity (Heffner and Heffner,
1986; Musiek et al, 1994; Murray and Fields,
2001). Whether or not pure-tone sensitivity
is affected by central auditory involvement
depends on the site and size of the lesion
and how soon the hearing sensitivity is
measured after the damage occurred (see
Heffner and Heffner, 1986).
An interesting observation made on this
patient, especially early on in the recovery
process, was that he would think that he
heard sounds that really did not exist. This
behavior has been seen in centrally deaf

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patients before (Musiek et al, 1994). We
cannot be sure if this phenomenon occurs
because the sounds are imagined in some
manner, such as an auditory illusion or
hallucination, or whether they are the result
of some other psychophysiological phenomenon.
Nonetheless, the patient genuinely believed the
sound(s) was indeed present in his
environment. The incidence of this
misinterpretation or illusion of sound appeared
to decrease as the patient’s hearing improved.
Anatomy and the MRI
This case is one that has some rather
specific neuroanatomy. Although there were
lesions in other areas of the brain, the only
significant auditory involvement was at the
right and left inferior colliculi. There may
have been some “minor” involvement in the
more caudal aspects of the superior colliculi,
which may have some auditory function. It
has been demonstrated that in some animal
species the superior colliculus may have some
auditory fibers. These, however, are in the
minority (Irvine, 1986). Therefore, the lesion
site in this case is one that is quite specific,
which helps in determining the role of the
inferior colliculus on the various aspects of
hearing function studied in the present
investigation.
Close inspection of the MRIs may indicate
that there was less damage at the more
anterior aspect of the colliculi. If this was in
fact the case, it may explain why there was
better hearing at the high frequencies than
at the low frequencies. The tonotopic
arrangement of the inferior colliculus has
been shown to progress from high to low
frequencies in a posterior to anterior manner,
with high frequencies located deep in the
midbrain (Merzenich and Reid, 1974). If the
deep substrate was damaged less, it may
have allowed the coding and progression of
the high-frequency stimuli up the remainder
of the auditory pathway. The severe damage
to the low-frequency region of the inferior
colliculus may have prohibited frequency
coding at this level and may have also either
stopped or disrupted the rostral flow of lowfrequency impulses to the thalamo-cortical
tract. This may also explain why the patient
reported during testing that the lowfrequency pure tones did not sound tonal.

Auditory Evoked Potentials
Major damage to the inferior colliculus
poses a situation that is of interest to the ABR,
MLR, and late potentials. It was once thought
that the inferior colliculus was the major
generator of the ABR wave V. Studies on
humans during neurosurgery changed this
thinking (Moller, 1983; Moller et al, 1995).
Current thinking is that wave V may have a
slight contribution from the inferior colliculus,
but that it is primarily generated by the
lateral lemniscus (see Hall, 1992). This case
adds information to what is currently known
about the wave V generator site. The
radiology shows that the damage was limited
to the inferior colliculus and possibly the
inferior portion of the superior colliculus but
that the pons was spared in this patient.
Although wave V is present, it is clear that
the waveform morphology is somewhat
compromised. This finding was repeated a
number of times. Therefore, it appears that
in this patient wave V may have some
contribution from the inferior colliculus in
addition to contributions from neural
structures located more caudally. The ABR IVV complex is clearly distorted in spite of the
fact that wave IV can be discerned from wave
V. In addition, the IV-V complex is
significantly smaller in amplitude than wave
I in both ears. This finding has often been
considered an indicator of a brainstem or
retrocochlear lesion (Musiek and Lee, 1995).
The early waves of the ABR are normal
bilaterally indicating good neural integrity in
the region of the caudal pons.
It is interesting to note that the ABR
waveform did not change over time and hence
did not reflect the improvement noted in the
patient’s behavioral hearing. This
disassociation may be related to several
factors. The auditory fibers in this area
(midbrain) may have recovered to some
degree and rerouted themselves around the
damaged area, or new fibers may have been
recruited to assume some of the functions of
the damaged neurons. It has been shown
that the inferior colliculus has the ability to
reorganize rather quickly when deprived of
peripheral input (Wang et al, 1996). In this
patient, this new or recovered neural
substrate may have supported the processes
necessary for the improvements noted in his
auditory behaviors but not have achieved
the neural synchrony or dipole orientation

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Journal of the American Academy of Audiology/Volume 15, Number 2, 2004

necessary to generate a normal ABR wave V.
We also know there is not a direct relationship
between behavioral hearing and the ABR
(Worthington and Peters, 1980). Hence,
behavioral changes may be reflected in
different measures than the ABR. The ABR is
dependent on neural synchrony, and perhaps
the fibers responsible for this synchrony did
not change but, rather, the change may have
occurred in neural substrate not involved
directly in the generation of the ABR.
The MLR that was recorded at three and
one-half weeks showed no readable response
for either ear at the Cz recording site. At 24
weeks there clearly was some recovery of the
MLR with the Pa wave visibly discernable for
both ears and across three electrode sites
(Cz, C5, C6). The tracings from the right ear
appeared to be slightly more synchronous
than those derived from left ear stimulation.
Although there was some definite recovery at
24 weeks in the MLR waveform morphology,
it did not continue to improve noticeably
beyond this time as waveforms at 10 months
were similar to those noted at 24 weeks. The
improvement in the MLR waves would again
support the notion that synchronous impulses
began making their way to the thalamocortical regions of the brain (see Kraus et al,
1994). In the initial MLR, this may not have
been the case. Again, the neural pathways in
the midbrain may have recovered or been
reorganized to allow synchronous impulses to
reach the generators of the MLR. Without
some form of recovery or auditory plasticity
occurring, it appears that bilateral damage
to the inferior colliculus may preclude
recording an MLR. Besides the auditory
thalamo-cortical pathways, the MLR
waveform may be dependent on the reticular
formation (see Kraus et al, 1994). Therefore,
it may be possible that compromise or a
“shutting down” of the reticular formation
may have compromised the MLR. There was
no asymmetry for the MLR waveforms across
electrode sites, indicating that the “effect”
was bilateral. This is consistent with the
lesion site being bilateral and symmetrical.
It is also interesting to note that the MLR
improved without any change in the ABR
late waves (IV-V). Therefore, one might
conclude that the MLR change was not
dependent on the same subcortical/brainstem
substrate as the ABR at least in this case. In
this regard, it has been shown previously

148

that an MLR can be present with an absent
ABR (Squires and Hecox, 1983).
The P300 as well as the N1 and P2 late
potentials were absent at the Cz recording site
at the initial evaluation, and there was
essentially no difference between the frequent
and rare waveforms. However, at nine weeks
the P300 did emerge along with rather
meager N1 and P2 complexes across all
electrode sites for both ears. The late
potentials all appeared to be delayed in
absolute latency. As with the MLR, these
late evoked potentials may have initially
been absent due to the lack of synchronous
input secondary to severe bilateral CANS
damage at the midbrain level. The emergence
of the N1, P2, and P300 potentials at nine
weeks may indicate (as with the MLR) the
reestablishment of a functional neural
pathway in the midbrain that could provide
synchronous input to the subcortex and
cortex. It seems important to point out that
without this “reestablished pathway,”
whether it is associated with recovery,
plasticity, or some other phenomenon, there
would be no cortical or event-related
potentials. What this suggests is that the
disruption of neural impulses at the level of
the midbrain can deprive the cortex of the
necessary input needed to generate its
potentials. It additionally suggests that there
is no other major pathway from the brainstem
to cortex other than that which courses
through the inferior colliculi that can provide
the synchronous input to the subcortical and
cortical pathways needed to generate the
middle and late potentials.
As with the MLR, it has been reported
that late evoked potentials can be obtained
even when the ABR is absent or severely
compromised (Squires and Hecox, 1983).
However, in these cases one must entertain
the possibility that there may have been
some plasticity factors involved (as discussed
earlier) and that perhaps even with an absent
ABR the inferior colliculus could have been
sufficiently intact to conduct the neural
impulses required for the generation of the
late potentials. It is well known that the
inferior colliculus is the main synaptic station
of the brainstem pathway and that when it
is severely damaged input to the next level
will be drastically reduced (van Noort, 1969).
It is reasonable to assume that since the
inferior colliculus is larger than any of the
more caudal auditory brainstem nuclei and

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since most of the ascending fibers from the
more caudal nuclei synapse at the inferior
colliculus, damage to the inferior colliculus
would have a greater effect on input to the
cortex than damage to the lower brainstem
structures (see Pickles, 1988 for review).
Given this scenario, it is logical to assume that
inferior colliculus damage of a severe degree
would have greater influence on the
propagation of mid and late potentials than
the lack of an ABR. Hence, it is our belief that
the mid and late potentials (and other
auditory processing at cortical levels) are
highly dependent on the integrity of the
inferior colliculi and that if CANS function at
this level had not improved in this patient
over time that the mid and late potentials
would have remained absent throughout the
period that this individual was followed.
The lack of “normal” auditory evoked
potentials at 10 months was more consistent
with the patient’s symptoms than were the
results of basic pure-tone and speech testing.
The patient still had problems hearing in
noise and in other complex listening
environments. It could be that the evoked
potentials and listening in noisy backgrounds
required a level of auditory processing
sophistication not yet supported by a partially
recovered neural substrate. These findings
clearly support the importance of using
electrophysiologic measures to document
auditory difficulties in many patients with
CANS involvement.
Intensity Discrimination
Intensity discrimination was measured
at five and 11 weeks. At five weeks the right
ear could not be tested due to poor threshold
sensitivity and inconsistent responses at the
frequencies tested (500, 1000, 2000 Hz). At
11 weeks, there was a rather marked
improvement in the patient’s performance
at all frequencies, with the most significant
change noted at 2000 Hz. In addition, a clear
binaural advantage for the intensity
discrimination task was observed. A similar
binaural advantage was also noted during
speech recognition testing in this patient, as
well as in other centrally deaf subjects
(Musiek et al, 1994). At 11 weeks, the patient’s
intensity discrimination, although noticeably
improved, was not normal, and this may
have been the key reason why the speech
recognition scores remained poor at this time.

We believe there is a relationship among
abnormal difference limens (DLs) for intensity
and frequency and poor speech recognition
scores. If the intensity (or frequency)
discrimination is so poor that one cannot
recognize changes in intensity (or spectral
information) from phoneme to phoneme, then
speech perception will suffer. Cranford and
colleagues (1982) in an investigation of
patients with temporal lobe lesions showed
increased DLs for frequency in ears that also
demonstrated reduced speech recognition
scores. This was especially evident when the
tone duration used in the DL test was
relatively brief. We also know of at least one
previous case of a patient with word deafness
in which the DLs for frequency were found
to be extremely large (Musiek et al, 1994). At
this time it is not possible for us to indicate
whether this is a common finding in patients
with central deafness since few of the previous
investigations reported in the literature have
undertaken this type of assessment. With
additional testing, a clear relationship
between intensity and frequency
discrimination abilities and speech
recognition performance may be documented.
Rehabilitation
The rehabilitation program for this
patient focused primarily on auditory training
with some work on language use and the
utilization of visual cues. It is difficult to
know how much of a roll the therapy played
in this patient’s auditory improvement.
Certainly much of the patient’s progress was
related to spontaneous recovery given the
time period over which most of the progress
was made. However, it is known that recovery
can often be enhanced by stimulation and by
presenting tasks to the central nervous
system that challenge it (see Musiek and
Berge, 1998, for review). It is therefore likely
that the patient’s improvement was positively
affected by the therapy activities in which he
participated. The patient’s progress in
therapy is reflected by the increased
sophistication in the tasks from the beginning
to the end of the formal sessions. At the
beginning, the patient’s identification and
discrimination had to do with gross, highly
different environmental sounds. At the end
of therapy he was working on differentiating
words, phonemes, and CVs that were highly
similar in their phonetic features. There is

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evidence that auditory training can improve
auditory abilities related to discrimination
and temporal processing (Recanzone et al,
1993; Kraus et al, 1995a, 1995b; Tallal et al,
1996), as well as other higher-level linguistic
processes. Therefore, it seems likely that the
therapy did make a contribution to this
patient’s recovery.
SUMMARY

T

here are a number of key observations
from this study that may be of interest to
the clinician and investigator. To our
knowledge, this is the first report of a case of
central deafness associated with damage to
both inferior colliculi. The audiological testing
of this patient demonstrated a wide range of
auditory deficits associated with profound
damage to both inferior colliculi. These
findings were consistent, for the most part,
with those noted for other cases with central
deafness originating from other structures
located more rostrally within the central
auditory nervous system. The most notable
difference was the observation of
abnormalities of wave V of the ABR. Although
such abnormalities would not be expected in
cases with compromise of cortical or
subcortical structures, these abnormalities
would also not have been predicted for the
present case based upon our current
understanding of the generator sites for the
ABR waves (Moeller, 1983). This finding
suggests that at least in this case the inferior
colliculus contributes to some degree to the
generation of wave V of the ABR. Also of
interest in this case was the observation of
a hierarchical course of recovery with the
patient demonstrating the ability to process
simple acoustic stimuli and tasks before he
could process auditory functions related to
more complex acoustic stimuli and tasks.
Unlike his performance on pure-tone, spondee
threshold and speech recognition testing, his
performance on other tests such as auditory
evoked potentials and intensity
discrimination did not recover to normal
values at 10 months. This may indicate a
disassociation in the physiologic bases of
these different types of tests and/or that
these types of tests have a different level of
processing sophistication. Finally, this case
adds to the growing body of evidence that
central auditory involvement can affect puretone sensitivity.

150

Acknowledgment. A special thanks to Michele
Abrams, Rosemarie Russo Ghezzi, Arlene Schwartz,
Paula Bacolini, Alyse Sicklick, Jacek Smurzynski,
and the Hitchcock Foundation for help and support
with this study.

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