782

J Neurol Neurosurg Psychiatry 2000;68:782–786

SHORT REPORT

Intact verbal description of letters with diminished
awareness of their forms
Kyoko Suzuki, Atsushi Yamadori

Section of
Neuropsychology,
Division of Disability
Science, Tohoku
University Graduate
School of Medicine,
2–1 Seiryo-machi,
Aoba-ku, Sendai
980–8575, Japan
K Suzuki
A Yamadori

Abstract
Visual processing and its conscious
awareness can be dissociated. To examine
the extent of dissociation between ability
to read characters or words and to be consciously aware of their forms, reading
ability and conscious awareness for characters were examined using a tachistoscope in an alexic patient. A right handed
woman with 14 years of education presented with incomplete right hemianopia,
alexia with kanji (ideogram) agraphia,
anomia, and amnesia. Brain MRI disclosed cerebral infarction limited to the
left lower bank of the calcarine fissure,
lingual and parahippocampal gyri, and an
old infarction in the right medial frontal
lobe. Tachistoscopic examination disclosed that she could read characters
aloud in the right lower hemifield when
she was not clearly aware of their forms
and only noted their presence vaguely.
Although her performance in reading
kanji was better in the left than the right
field, she could read kana (phonogram)
characters and Arabic numerals equally
well in both fields. By contrast, she
claimed that she saw only a flash of light in
61% of trials and noticed vague forms of
stimuli in 36% of trials. She never recognised a form of a letter in the right lower
field precisely. She performed judgment
tasks better in the left than right lower
hemifield where she had to judge whether
two kana characters were the same or different. Although dissociation between
performance of visual recognition tasks
and conscious awareness of the visual
experience was found in patients with
blindsight or residual vision, reading (verbal identification) of characters without
clear awareness of their forms has not
been reported in clinical cases. Diminished awareness of forms in our patient
may reflect incomplete input to the extrastriate cortex.

Correspondence to:
Dr K Suzuki
kyon@mail.cc.tohoku.ac.jp

Keywords: blindsight; alexia; consciousness; letter
discrimination

Received 19 August 1999
and in revised form
23 December 1999
Accepted 5 January 2000

Dissociation between a cognitive processing
and conscious awareness of the processing is

(J Neurol Neurosurg Psychiatry 2000;68:782–786)

one of the stimulating topics of neurology, but
neural mechanisms underlying the conscious
awareness remained unsolved.1 2 This dissociation was most often reported in visual processing. For example, lesions aVecting the primary
visual cortex (V1) can uncouple visual discrimination and awareness. A patient with the
V1 lesion sometimes showed discrimination of
visual stimuli without conscious awareness—
that is, blindsight.3–6 In addition, recent studies
reported residual vision that was not always
associated with clear awareness of stimuli in
patients with striatal lesions.7–12 In these
studies, awareness for visual stimuli was examined by methods which require minimal verbal
expression, such as forced choice responses
about a property or yes/no detection paradigm.
On the other hand, verbal identification of
stimuli without clear awareness of their forms
has not been reported in clinical cases. We
report on a patient with alexia who could read
characters aloud presented to the right lower
quadrant field without clear consciousness of
their forms and we attempt to elucidate neural
mechanisms of conscious awareness.
Case report
A 48 year old right handed woman with 14
years of education was admitted to a hospital
because of an inability to read. The patient had
experienced transient weakness of her right leg
3 years before and at the same time an
aneurysm of the anterior communicating
artery was incidentally found and clipped. One
and half months later, the patient was referred
to our hospital for rehabilitation. Neurological
examination on admission showed incomplete
right homonymous hemianopia, slight right
hemiparesis, alexia, anomia, and amnesia.
Other cranial nerves and cerebellar function
were intact. Deep tendon reflexes were symmetric without pathological reflexes. There was
no visual agnosia or prosopagnosia. A Humphrey visual analyser demonstrated right homonymous hemianopia sparing a part of the
lower medial field (fig 1). Corrected visual
acuity was normal. Brain MRI showed a
cerebral infarction in the left lingual and parahippocampal gyri and a part of the splenium,
and an old lesion in the right medial frontal
area associated with the previous clipping procedure (fig 2). Blood flow measured with 123IIMP single photon emission tomography

783

Intact verbal description of letters with diminished awareness of their forms

(SPECT) showed a decrease in blood flow in
the territory of the left posterior cerebral artery
and in the right medial frontal lobe. A whole
head magnetometer combined with MRI
showed a visual evoked field (P100m response)
–30

–20

–10

0

10

20

30

–30

in the right medial occipital lobe corresponding
to the stimuli in the left visual field, but no clear
responses to those in the right visual field. The
following neuropsychological evaluation was
performed during the next 2 months. All
–20

–10

0

10

20

30

0

–30

Figure 1
field.

Visual fields assessed with a Humphrey visual analyser showing right homonymous hemianopia with spared region in the right medial lower

Figure 2

T1 weighted MR images demonstrated cerebral infarction in the left striate, lingual, and parahippocampal gyri and a part of the splenium.

30

784

Suzuki, Yamadori

experimental investigations were performed in
compliance with the relevant laws and institutional guidelines. She gave informed consent
before the examination.
READING ABILITY AND AWARENESS RESPONSES

Systematic neuropsychological examination
was performed to show the nature of her deficits. She was alert, cooperative, and fully
oriented all the time. Language was evaluated
by the standard language test for aphasia in
Japanese (SLTA), which was developed to
examine various aspects of language ability for
native Japanese speakers and has been used as
a standard test for more than 20 years in Japan.
Her overall performance on the SLTA was
normal except for anomia and severe alexia
with kanji (ideogram) agraphia. Her verbal
utterances were fluent without any paraphasia.
Her comprehension of spoken speech and repetition was good. She made seven errors out of
20 in confrontation naming. Writing was
preserved for two types of hiragana (phonogram) and simple kanji characters but not for
complex kanji characters. We defined simple
kanji characters as those learnt by 9 years of age
at a primary school, most of which consist of
less than seven or eight strokes. She was significantly impaired in the reading aloud and reading comprehension subtests. In the reading
aloud task, she made three errors out of 10 for
kana and kanji words and two errors for Arabic
numerals. She used letter by letter strategy and
her time for reading was prolonged as the
number of characters increased. In the
Wechsler adult intelligence scale-revised, her
verbal IQ was 94, and her performance IQ was
62. A substantial memory deficit was evidenced on the Wechsler memory scale-revised.
The patient had a verbal memory index of 58,
a visual memory index of 92, and a general
memory index of 61. In summary, her
neuropsychological impairment included
alexia characterised by letter by letter reading,
mild agraphia for kanji, anomia, and amnesia
for verbal material. Her ability to read hiragana
and kanji words had not changed markedly
Tachistoscopic examination and awareness responses in each visual field

Task 1: Pointing
Kana letters
Kanji letters
Arabic numerals
Kana words
Objects
Colours
Patterns†
Task 2: Judgement of Kana letters*
Awareness responses**
Unaware: no feeling of something being there
Vague: a feeling of a flash of light
Vague recognition of the form
Aware: certain of the form
Task 3: Read aloud
Kana letters
Kanji letters**
Arabic numerals
Total correct responses
Awareness responses**
Unaware: no feeling of something being there
Vague: a feeling of a flash of light
Vague recognition of the form
Aware: certain of the form

L lower quadrant field

R lower quadrant field

25/32
28/32
27/32
4/8
8/8
2/8
7/8
22/24

23/32
25/32
26/32
5/8
4/8
4/8
5/8
15/24

0/24 (0.0%)
0/24 (0.0%)
2/24 (50.0%)
22/24 (95.5%)

0/24 (0.0%)‡
17/24 (58.8%)
7/24 (71.4%)
0/24 (0.0%)

23/24
22/24
11/24
56/72

21/24
13/24
17/24
51/72

0/72
0/72
5/72 (20.0%)
67/72 (82.1%)

2/72 (0.0%)‡
44/72 (70.5%)
26/72 (76.9%)
0/72

*p<0.05; **p<0.005. †Meaningless patterns with several straight and curved lines.

during her stay, as confirmed by comparable
results of a shortened version of reading tests
performed in the 6th and 10th week.
We further investigated her reading ability in
both visual hemifields to clarify her visual recognition and conscious awareness for it in the
9th week postonset (table). Tachistoscopic
examination required the patient to sit 50 cm
away from a high resolution red-green-blue
colour monitor of a Power MacIntosh 6200/75
computer, with her eyes aligned with a fixation
cross in the middle of the screen. An examiner
always monitored her eyes to ensure that she
was fixating the cross during stimulus presentation. A stimulus, the width of which was a
visual angle of 1 to 2 degrees, appeared for 100
ms in the right or left lower visual field at a
visual angle of 2 to 3 degrees from the vertical
meridian. Thus stimuli were presented in the
area where visual stimuli with increased
luminance, about 10 dB above those in the
intact left visual field, could be detected. Her
ability to match, discriminate, and read stimuli
was examined. Seven types of stimuli were used
for matching; one hiragana letter, one kanji letter that corresponded to a concrete word, one
or a pair of Arabic numerals, a hiragana word
that consisted of two characters and corresponded to the same concrete word as the kanji
letter stimulus, a line drawing of an object, colour, and a meaningless pattern with several
straight and curved lines. The complexity of
meaningless patterns was almost equal to that
of kanji characters. She was asked to point to
the same one as a stimulus out of eight items
from the same category just after the stimulus
presentation (task 1). Discriminative function
was also measured in which the patient was
asked whether two kana characters vertically
presented in one lower field were same or
diVerent (task 2). Her ability to read characters
was examined using three types of stimuli: kanji
characters, kana characters, and Arabic numerals. She was requested to read a letter aloud just
after the stimulus presentation (task 3). During
tasks 2 and 3, she was asked what she saw and
how clear the stimulus was and she answered
orally. There were 48 trials for each type of
stimulus, randomly presented in both visual
fields (half of the trials in each field) in tasks 2
and 3. Task 3 was repeated on two separate
days to confirm the reproducibility of the data.
In task 1, her performance on matching for
each stimulus group was not significantly
diVerent between two lower quadrant fields (÷2,
p>0.05). In task 2, judging ability in both visual
fields was diVerent from each other (÷2,
p<0.05). Her awareness responses for stimuli
in the right lower visual field were, however,
more significantly impaired compared with
those in the left lower field (Mann-Whitney
test, p<0.005). In 17 out of 24 trials, she
denied having seen any form but said that she
saw a flash of light in the right field. In task 3,
although reading kanji characters was significantly impaired in the right lower visual field
(÷2, p<0.005), she could read kana characters
and Arabic numerals at the same level in both
visual fields (÷2, p>0.05; table). By contrast, she
declared that she saw only a flash of light in 44

Intact verbal description of letters with diminished awareness of their forms

out of 72 trials although she read them aloud
correctly in 70% of trials. Her awareness
responses for stimuli in the right lower visual
field were significantly lower than those in the
left lower field (Mann-Whitney test, p< 0.005).
She often declared that she could not understand how it was possible for her to read the
letter aloud when she saw only a flash of light.
The ratio of correct responses in the right lower
field was not diVerent between the trials when
she saw only a flash of light and those when she
was aware of vague forms of characters.
Discussion
The present data demonstrate a clear dissociation between our patient’s ability to read characters and her ability to be aware of their forms.
She was able to extract “verbal” information of
a stimulus without clear awareness of its intrinsic visual information—that is, form. We think
that this is the first clinical report that processing of complex visual pattern-like characters
can occur without clear visual awareness of
their form. Dissociation between visual awareness and visual recognition was reported in
normal volunteers by modulating stimuli.
Adams showed that with very brief, masked
presentation subjects could identify orthographic stimuli without being able to report
accurately the case or font of their
presentation.13 Normal subjects could report
the location of a stimulus at better than chance
accuracy when they claimed no form perception, because of short exposure duration and
pattern masking.14 By superimposing complementary textures, such as opposite motion or
binocular rivalry and orthogonal orientation,
normal subjects could locate the texture
contrast reliably but not consciously experience it.15
Previous studies suggested uncoupling between visual awareness and discrimination in
cases with cortical blindness or hemianopia,—
that is, blindsight. Patterns of impaired and
preserved abilities in cases of blindsight show
considerable variability from case to case. Most
patients could detect and localise a light.10
Some patients could discriminate orientation
and shape, and detect movement and
flicker.3 16 17 Patients with blindsight have usually no phenomenal experience of seeing a
processed stimuli at all; but some may
experience a type of contentless awareness or a
feeling of something happening. Total unawareness and a vague feeling of a stimulus may
be experienced, as reported in patient GY who
demonstrated a marked variability in his
awareness for a given level of discrimination of
motion direction.18 In addition, residual vision
in patients with striatal lesions was not associated with relevant awareness for visual stimuli.
Blythe et al reported patients with residual
vision who demonstrated ability to localise
visual target by eye movements and hand
reaching when they experienced a transient
shadow in the “blind” field and could not
identify any characteristic of the stimulus.10
Patient DB could report horizontal or vertical
lines and discriminate X or O above chance
level. During these experiments his most com-

785

mon response was that he saw nothing at all,
but, if pressed, he said that he had a “feeling”
that the stimulus was either pointing this or
that way and smooth (the O) or jagged (the
X).7 Marcel reported on two patients with
homonymous right hemianopia who demonstrated conscious and non-conscious perception of shape in the blind field.19 Their
conscious visual experience was, however, only
a dark shadow or a flash, not shape. In
summary, patients with blindsight or residual
vision sometimes felt or noticed the presence of
stimuli, but this vague awareness was uncoupled with the visual processing that was
actually done during tasks.
Dissociation between visual processing and
conscious awareness in our patient was similar
to these patients in a sense that conscious
awareness was not enough for the task to be
solved. But our patient was diVerent in that she
showed descriptive ability of characters when
she was aware of stimulus presentation, but not
clearly aware of the form. In other words, she
was somehow able to extract the essential
attribute of a stimulus—that is, its name—but
was unable to consciously recognise its form
and had no idea whether the answer was
correct or not. Her responses were not mere
uncertainty about the answer, but she could
not tell whether they had any certain form and
saw a flash of light instead. In reported patients
with residual vision whose lesions were confirmed in the striate and extrastriate cortices,
they could discriminate one of two shapes or
characters but could not describe characters
verbally. Patient GY reported some sort of
form when presented with words like “waves”
which were straight or curved, or a “squareness”, but could not read the words.6 Patients
DB and TP answered “smooth” or “jagged” in
letter discrimination tasks when pressed to say,
but they could not name the letter.7 19
Lesions in our patient involved the striate
and peristriate cortex below the calcarine
fissure in the left hemisphere. The left lingual
gyrus was included in the lesions, but the fusiform gyrus was spared. A patient with lesions
in the right lower bank of the calcarine fissure
and the lingual gyrus demonstrated unconscious visual processing in the left upper field
that was related to the remaining islands of
vision from preserved striate cortex.12 It is
assumed that people may not be aware of some
of the neuronal activity in the V1.1 Patients who
hallucinate have increased ventral extrastriate
activity which persists between hallucinations.20 They found that the rise in functional
magnetic resonance imaging (fMRI) occurred
before the onset of the conscious visual experience (hallucination) without visual input. The
possible explanation may be that cerebral
activity has to exceed a certain threshold level
to contribute to visual consciousness. A study
using fMRI for patient GY demonstrated
that there was a relation between conscious
awareness of motion and cerebral activity
in area V5 and in the reticular activating
system.18 Thus activity in the extrastriate cortex above some threshold might be necessary
to acquire conscious visual processing. Recent

786

Suzuki, Yamadori

neuroimaging and neurophysiological studies
showed the importance of the fusiform gyrus
for reading.21 22 In our patient we speculate
that the spared left fusiform gyrus received
enough visual information about characters to
read them aloud, probably via the residual V1
(cuneus), but the amount of activity in the
extrastriate cortex might not have been
suYcient to evoke conscious experience of
their forms.
This research was partly supported by grants (No 10557059
and No 09770436 to KS) from the Ministry of Education, Science and Culture, Japan. We are grateful to Dr Ogawa for referring the patient and to Drs Nakasato and Hatanaka for helping
us to perform magnetoencephalography.
1 Crick F, Koch C. Consciousness and neuroscience. Cerebral
Cortex 1998;8:97–107.
2 Schacter DL. Implicit knowledge: new perspectives on
unconscious processes. Proc Natl Acad Sci USA 1992;89:
11113–7.
3 Weiskrantz L, Barbur JL, Sahraie A. Parameters aVecting
conscious versus unconscious visual discrimination with
damage to the visual cortex (V1). Proc Natl Acad Sci USA
1995;92:6122–6.
4 Sanders MD, Warrington EK, Marshall J, et al.
“Blindsight”: Vision in a field defect. Lancet 1974;i:707–8.
5 Shefrin SL, Goodin DS, AminoV MJ. Visual evoked potentials in the investigation of “blindsight”. Neurology 1988;38:
104–9.
6 Weiskrantz L. Blindsight. Oxford: Clarendon Press, 1986.
7 Weiskrantz L, Warrington E, Sanders M, et al. Visual capacity in the hemianopic field following a restricted occipital
ablation. Brain 1974;97:709–28.

8 Weiskrantz L. Varieties of residual experience. Q J Exp Psychol 1980;32:365–86.
9 Barbur J, Ruddock K, Waterfield V. Human visual responses
in the absence of the geniculo-calcarine projection. Brain
1980;103:905–28.
10 Blythe IM, Kennard C, Ruddock KH. Residual vision in
patients with retrogeniculate lesions of the visual pathways.
Brain 1987;110:887–905.
11 Ceccaldi M, Mestre D, Brouchon M, et al. Autonomie
déambulatoire et perception visuelle du mouvement dans
un cas de cécité corticale quasi totale. Rev Neurol (Paris)
1992;148:343–9.
12 Fendrich R, Wessinger CM, Gazzaniga MS. Residual vision
in a scotoma: implications for blindsight. Science 1992;258:
1489–91.
13 Adams MJ. Models of word recognition. Cogn Psychol 1979;
11:133–76.
14 Meeres SL, Graves RE. Localization of unseen visual stimuli
by humans with normal vision. Neuropsychologia 1990;28:
1231–7.
15 Kolb FC, Braun J. Blindsight in normal observers. Nature
1995;377:336–8.
16 Perenin M. Discrimination of motion direction in perimetrically blind fields. Neuroreport 1991;2:397–400.
17 Stoerig P, Cowey A. Blindsight in man and monkey. Brain
1997;120:535–59.
18 Zeki S, Ffytche DH. The Riddoch syndrome: insights into
the neurobiology of conscious vision. Brain 1998;121:25–
45.
19 Marcel AJ. Blindsight and shape perception: deficit of visual
consciousness or of visual function? Brain 1998;121:1565–
88.
20 Ffytche D, Howard R, Brammer M, et al. The anatomy of
conscious vision: an fMRI study of visual hallucinations.
Nature Neuroscience 1998;1:738–42.
21 Nobre A, Allison T, McCarthy G. Word recognition in the
human inferior temporal lobe. Nature 1994;372:260–3.
22 Büchel C, Price C, Friston K. A multimodal language region
in the ventral visual pathway. Nature 1998;394:274–7.