Neurop~ychobgq

Vol. 21, No

6, pp. 699-704

0028

1983

3932/83$3.00+0.00

c 1983 PergamonPressLtd

PrInted
I"GreatBnta~n.

NOTE
“LATE”

RECOVERY OF THE RIGHT EAR DICHOTIC SCORE FOLLOWING
CEREBROVASCULAR
ACCIDENT: A CASE REPORT

Hennepin

NANCY

NICCUM*

County

Medical

and ALAN B. RUBENS
Center,

(Accqtrd

Minneapolis,

3 May

MN, USA

1983)

Abstract-Late
recovery of the right car score on a digit dichotic listening test was observed in a 45yr-old female patient. The right ear score was at chance levels of accuracy through the ninth month
post-onset of a cerebrovascular
accident and then improved dramatically
to 67 “/, correct by month
12. Possible bases for this pattern of performance
are discussed

INTRODUCTION
THE EVOLUTION of performance
on dichotic listening tests for patients recovering from aphasia has been the focus of
a great deal of interest in recent years. Most investigators
have been primarily interested in changes that occur
during the first 336 months post-onset
of symptoms.
Reasons for interest in this initial phase of recovery vary
depending
upon which of two common interpretations
of dichotic listening scores is adopted by a particular
investigator.
One interpretation
of the dichotic scores maintains that the direction and magnitude of the asymmetry between
ears reflect hemispheric
dominance
for language processing.
When this interpretation
is adopted for aphasic
subjects, the investigators
are often interested in determining whether language recovery is mediated by transfer of
dominance to the right hemisphere or by reorganization
of function in the left hemisphere [I, 3,581. Johnson et al.
[3] pointed out that “the greater portion of language recovery usually takes place in the first six months following
aphasia onset” (p. 127) and thus any changes in language dominance that mediate recovery might also be expected
to occur during this time. They in fact found that “increases
in the magnitude
of language
improvement
accompanied
increases in the magnitude of the LEP [left ear preference]”
(p. 127) and this finding was interpreted
as evidence that the right hemisphere was mediating language recovery. However, the relationship
between LEP
and the degree of language recovery was only significant for patients who were less than 6 months post-onset.
The other interpretation
of dichotic listening scores observed for aphasic patients is that the scores reflect “lesion
effects”. This interpretation
assumes that lesions of the auditory pathways can result in degradation
of the signal
that may, as SCHULHOFF and GCIODGLASS [9] stated, “interact
with and possibly override the premorbid
ear
asymmetry so that dominance can no longer be inferred” (p. 157). Changes in the dichotic listening scores might
also be expected to be most pronounced
during the first months post-onset of symptoms under the lesion effect
interpretation
since the majority of physiological recovery is thought to occur during this time [4]. However, we will
describe a case in which dramatic changes in dichotic listening performance
were observed more than 9 months after
a cerebrovascular
accident that resulted in aphasia.

METHOD
The patient was a 45-yr-old, right-handed,
white female with a high-school education and no history of a prior
neurological
event. Etiology of the present illness was cerebrovascular
accident. The patient exhibited right
hemiplegia and a non-fluent aphasia soon after admission. She was seen by us at monthly intervals from 1 to 6
months post-onset
of symptoms and again at months 9. 12, 15 and 24 (only a limited subset of the tests was
*To whom correspondence
U.S.A.

should

be addressed

at: 1626 Adams

Street Northeast,

Minneapolis,

MN 55413.

NOTE

700

completed at months 15 and 24). She exhibited a right superior homonymous
quadrantanopsia
at month I. but
visual fields were normal on subsequent months. The hemiparesis, greater in the arm than the leg, persisted over the
12-month period of evaluation, with some proximal improvement.
A moderate-to-mild
right-sided hypesthesia was
also present on all examinations.
Position sensation was intact, but graphesthesia
and stereognosis were severely-tomildly impaired in the right hand throughout
testing.
A schematic representation
of the lesion location for this patient is shown together with four cuts from the
computerized
tomographic
(CT) scan in Fig. I. The lesion included almost the entire insula and white matter
subjacent to it. It extended medially into portions of the putamen, globus pallidus, internal capsule and the midportion of the callosal/corona
radiations. Lateral extension to the cortical surface was noted in three locations: the
frontal operculum, the suprasylvian portion of the supramarginal
gyrus, and in what appeared to be Heschl’s gyrus
on the superior temporal surface.
Stimuli

and procedures

Stimuli included in thedichotic
test were the numbers l-6. Tokens, spoken by a male talker, weredigitizedand
the
onset of energy in the digitized waveforms was used as the reference for aligning stimuli within pairs. Thirty different
pairs of stimuli were created by combining each of the six digits with the other five in the two possible stimulus-tochannel orientations.
The dichotic digit test and the Neurosensory
Center Comprehensive
Examination
for Aphasia (NCCEA) were
given each month. The Boston Diagnostic Aphasia Examination
(BDAE) was administered
at months I, 3,6,9, 12
and 15. Dichotic tests were given in a sound-treated
booth (Korfund, Noiseguard) and the stimuli were presented at
80 dB SPL bilaterally. The monotic conditions consisted of the identification
of 30 stimuli/ear and the order in
which ears were tested was alternated across months. The dichotic conditions consisted of the identification
of 60
pairs of stimuli. Channel-to-ear
orientations
were counterbalanced
across months and reversed after the first 30
pairs within months.

RESULTS
Audiometric
tests revealed bilaterally symmetrical thresholds (within IO dB) within the normal range of hearing
for pure tones at the octave frequencies 25&4000 Hz and for spondaic words. Language tests revealed a severe
impairment at month 1.The patient had almost no spontaneous
speech at that time and auditory comprehension
was also moderately impaired. The patient was classified as having a mixed anterior aphasia at that time. Table 1
shows percentile scores for the Token Test and the sentence repetition subtest of the NCCEA along with the mean
z-scores for auditory comprehension
and phrase repetition on the BDAE. Auditory comprehension
improved
dramatically by month 2 and had returned to near normal levels by month 4. Sentence repetition remained severelyto-moderately
impaired throughout
testing. Although spontaneous
speech was still severely limited at month 3, the
patient was fluent. She was rated on the BDAE profile of speech characteristics
as having a phrase length of 5. with
frequent paraphasias
and near-normal
sentence intonation
and articulation.
The pattern of performance
on the
language tests after month 1 was thus felt to be consistent with the diagnosis of conduction
aphasia.
Table 1. Performance
levels on the Token Test and the sentence repetition
in percenttle scores, and performance
levels on the auditory comprehension
the BDAE are shown as mean z-scores
Months

NCCEA: percentiles
Token Test
Sentence repetron
BDAE: mean z-scores
Auditory comprehension
Phrase repetition

subtest of the NCCEA
and phrase repetition

are shown
subtests of

post-onset

1

2

3

4

5

6

9

12

15

2
2

55
6

56
13

70
16

71
16

72
13

78
13

90f
41

YOf
33

t-o.89
-0.91

f0.98
+0.09

-0.09
+0.41

+ I .05
+ 0.09

PO.65
- I .06

f0.66
-0.57

Monotic scores on the digit test were slightly reduced for both ears at months I and 2 (left edr = 93 and X3 ‘>,, rtght
ear= 77 and X7 90 respectively), but were at a ceiling in all subsequent months. The dichotic scores on the digit test
are shown in Fig. 2. The left ear (LE) dichotic score approached
monotic accuracy levels in all months. The right ear
(RE) score was at chance level through month 9. but unlike any other patient we have tested, improved dramatically
to 67’s, correct at month 12. This improvement
was replicated at 15 and 24 months post-onset. Although the right
ear score did not improve above chance levels until month 12, the patient indicated in earlier months that she was
able to detect the presence of a different stimulus in the right ear.

701

FIG. I. Two sections from the CT-scan are shown in panels A and B. Low attenuation
in the insular
region and extension to the cortical convexity on the superior temporal surface can be seen in these
sections. Panels C and D are sagittal reconstructions.
The low attenuation
that extended to the
cortical convexity in panel B is inferior to the Sylvian fissure and appears to involve Heschl’s gyrus.
The low attenuation
at the tip of the Sylvian fissure involves the supramarginal
gyrus above the plane
of the section shown in panel B. A schematic representation
of the lesion locations is shown on the
right. Diagonal lines indicate areas with lateral extension to the cortical surface and gray shading
indicates involvement of the insula and subjacent deep structures.

NOTE

703

OC

I
Months

FIG. 2. Changes

in the right (0)

Post - Onset

and left ( x ) ear scores over time on the digit dichotic

test.

DISCUSSION
The only change in dichotic listening performance
observed for this patient during the first 9 months post-onset of
aphasia was an increase in the LE score between months 2 and 3. This improvement mirrored the patient’s ability to
accurately identify the digits in the monotic conditions, and thus probably was not a dichoticchangeattributable
to
a shift in cerebral dominance
for language.
A dramatic change in performance
on the dichotic digit test did occur between months 9 and 12. The RE score
improved from chance levels of accuracy at month 9 to 67 % correct at month 12, and this improvement
was
replicated at months 15 and 24. As pointed out in the introduction,
both “dominance
effect” and “lesion effect”
interpretations
would seem to predict that the major changes in dichotic listening performance
should occur during
the first 3-6 months post-onset
of symptoms, and thus performance
for “chronic”
aphasic patients should be
relatively constant. Therefore it is of interest to speculate about the basis of the “late” recovery of the RE score
observed for this patient.
First, however, we should point out that although the RE score did not change appreciably
during the first 9
months, gradual recovery of the neurological
substrate could still have been taking place. We in fact have evidence
in the form of a subjective report by the patient that some recovery had occurred as early as month 3. The patient
seemed surprised to hear two stimuli in the dichotic condition in that month and indicated that she thought the
examiner had been “lying” on previous months regarding the presence of two different numbers. Thus it seems that
the dichotic pairs were initially perceived as a single number. That perception changed to the point where a second
number could be detected but could not be identified, and finally improved to the point where the patient could
correctly identify the second number on two-thirds of the pairs. The dramatic improvement
that occurred between
months 9 and 12 may have represented a “threshold effect”, that is. the improvement
in the integrity of the RE
signal may not havecrossed
the “threshold ofspeech intelligibility” until after month 9. Thus it is impossible to infer
from the data whether the underlying process was continuous
or discontinuous.
The hypothesis
that RE performance
reflects the integrity of the RE signal falls within a “lesion effect”
interpretation
of dichotic listening. Under this interpretation
it is surprising that the RE ever did exceed a score of
approximately
SO’?;,correct. We have indicated in previous reports that chronic patients with CT-scan evidence of
involvement of the geniculo-cortical
system do not obtain RE scores on our digit dichotic test of greater than SO”,
correct [6. 71. However. this patient appeared to have a very unusual lesion such that the temporal lobe component
was restricted almost entirely to the region of Heschl’s gyrus.
This pattern of performance could be accounted for in a variety of ways within a lesion effect interpretation.
First,
it is possible that our reading of the CT-scan was incorrect and that the primary auditory cortex was spared. One
would then have to speculate that a dysfunction
of the geniculo-cortical
system, caused by the proximity of the
lesion, persisted through
month 9. Second, if Heschl‘s gyrus was only partially lesioned or if contralateral
connections
exist from the RE to “surrounding
auditory cortex” 121. then a portion of the auditory fibers could
have been spared. Both physiological
recovery and considerable
recovery of auditory processing abilities may have
been necessary before the patient could accurately
identify the meager remaining contralateral
input. A third
possibility is that the patient’s improving linguistic abilities may have enabled her to correctly identify the RE signal
that traveled ipsilaterally to the right hemisphere and then may have been transferred
to the left hemisphere via
callosal connections (as is thought to occur for the LE signal in non-brain-damaged
listeners). Finally, it is possible
that some functional regeneration
occurred in the geniculo-temporal
system. This conceivably could have taken

704

NOTE

place by virtue of gradual regeneration
or collateral sprouting
[IO] in partially spared auditory cortex or by
remyelination
of the geniculo-temporal
pathway.
The dominance effect interpretation
of dichotic listening performance
cannot account for the present findings.
The evolution of scores for the two ears or for the ear advantage was clearly not related to language performance.
If
such a relationship
had existed, then we should have observed dramatic recovery of language function between
months 2 and 3 and/or between months 9 and 12. Inspection of the data presented in Table I, however, indicates
that this was clearly not the case. The patient’s auditory comprehension
had returned to near-normal
levels prior to
6 months post-onset
of symptoms. One of the largest changes in auditory comprehension
that was observed
occurred between months 1 and 2, a period during which dichotic performance
did not change appreciably.
We do not know whether recovery occurs this late in other modalities. Detailed long-term recovery studies in
humans have not been reported for the somatosensory
or visual systems, and thus it is possible that such recovery
may in fact occur. The documentation
of recovery patterns in the auditory system is important because it points to
time post-onset as being a critical variable in dichotic listening studies involving brain-damaged
populations.
and it
eventually may help us to understand
the nature and time course of physiological
recovery from a stroke.
Ackno~L,/e~~emrnfs~~This research was supported by NINCDS Contract NOI-NS-237X. The authors would like to
thank DAVID S. KNOPMAN and DCWGLAS YOCK for their comments regarding the CT-scan and OLA A. SELNESfor his
contributions
concerning interpretation
of data from the language tests.

REFERENCES
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Lunq. 10, 145-~151, 1980.
2. GALABURDA, A. and SANIDES, F. Cytoarchitectonic
organization
of the human auditory cortex. J. camp.
Neural. 190, 597-610, 1980.
3. JOHNSON, J. P., SOMMERS,R. K. and WEIDNER, W. E. Dichotic ear preference in aphasia. .I. Speech Hew. Res. 20,
116-129, 1977.
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