Varieties of Alexia From Fusiform, Posterior Inferior Temporal and Posterior Occipital Gyrus Lesions
Varieties of alexia from fusiform, posterior inferior temporal and posterior occipital gyrus lesions
Yasuhisa Sakurai 0
0 Department of Neurology, Mitsui Memorial Hospital , 1 Kanda-Izumi-cho, Chiyoda-ku, Tokyo, 101-8643 , Japan Tel.:
Reading impairments of three alexia patients, two pure alexia and one alexia with agraphia, due to different lesions were examined quantitatively, using Kanji (Japanese morphogram) words, Kana (Japanese phonetic writing) words and Kana nonwords. Kana nonword reading was impaired in all three patients, suggesting that widespread areas in the affected occipital and occipitotemporal cortices were recruited in reading Kana characters (corresponding to European syllables). In addition, the findings in patient 1 (pure alexia for Kanji and Kana from a fusiform and lateral occipital gyri lesion) and patient 2 (pure alexia for Kana from a posterior occipital gyri lesion) suggested that pure alexia could be divided into two types, i.e. ventromedial type in which whole-word reading, together with letter identification, is primarily impaired because of a disconnection of word-form images from early visual analysis, and posterior type in which letter identification is cardinally impaired. Another type of alexia, alexia with agraphia for Kanji from a posterior inferior temporal cortex lesion (patient 3), results from deficient whole-word images of words per se, and thus should be designated “orthographic alexia with agraphia.” To account for these impairments, a weighted dual-route hypothesis for reading is suggested.
Pure alexia (alexia without agraphia) is defined as
the inability to read printed material while writing is
]. Dejerine suggested that pure alexia is
induced by any lesion that interrupts visual input to
the angular gyrus, in which visual images of words
and letters are stored [
]. Geschwind  stressed
the importance of the splenium lesion in pure alexia.
He claimed that damage to the splenium prevents the
interhemispheric transmission of visual information in
written language. However, subsequent lesion studies
showed that pure alexia can occur without a splenium
]. In fact, this point had already been
predicted by Dejerine. Greenblatt  classified this
nonclassical type of alexia [
] into occipital alexia and
subangular alexia, claiming that both types of alexia
can be accounted for by the interruption of association
fibers to the angular gyrus. Presently, the anatomic
substrate of pure alexia is considered to be in the
paraventricular white matter of the left occipital lobe [
the lingual and fusiform gyri including the white
], or the ventral occipitotemporal area [
Conversely, converging findings from neuroimaging
studies have revealed that the ventral occipitotemporal or
posterior inferior temporal cortices (Brodmann Area
[BA] 37) are essential in reading [
Letter-by-letter reading observed in pure alexia has
received attention from cognitive psychologists [
]. The patients cannot read regular words (that
obey spelling-sound rules) or irregular words and
depend on letter-by-letter reading . Therefore, longer
words are read far more slowly than shorter words
(word-length effect). Kinesthetic reading, i.e.
tracing letters with the fingers, is a strategy for
letter-byletter readers to compensate for reading difficulty [
Letter-by-letter readers are impaired at letter
], but some of them can make
lexical decisions and semantic categorization, even though
they cannot explicitly identify the stimulus [
Moreover, some patients show a frequency effect
(highfrequency words are recognized better or faster than
low-frequency words) and imageability effect
(imageable words are recognized better or faster than
nonimageable words), which is more marked in longer
]. Theoretically, letter-by-letter reading
was suggested to be derived from impaired ability to
process letters by whole word recognition units, and
thus was called word-form dyslexia .
According to this view, the word-form system is responsible
for segmenting letter strings into recognizable units,
such as letters, syllables, morphemes and words.
Another suggestion was that letter-by-letter readers are not
able to gain access to the orthographic lexicon from
The Japanese language has two distinct writing
systems; i.e. Kanji (ideograms or morphograms, originally
adopted from Chinese characters) and Kana (Japanese
phonetic writing or syllabograms, originally taken from
Kanji characters). Kana are further divided into
Hirakana (cursive Kana, examples here are all this form)
and Kata-kana (square Kana that are used primarily for
representing loan words). Kanji are graphically
complicated and have meaning as well as two ways of being
read: the on-reading that conveys the phonetic value;
and kun-reading that conveys the meaning (e.g. [ji] by
on-reading and [toki] by kun-reading, meaning “time”).
Kanji words consist of more than two Kanji or are
accompanied by Kana suffixes, and usually have one
reading attached to the meaning (e.g. [tokei], clock;
[hakaru], measure). Therefore, reading of Kanji words
requires whole-word recognition as well as individual
character identification. In contrast, Kana are
graphically simple and have one definite phonetic value and
no intrinsic meaning (e.g. [to]). Kana words consist
of one or more Kana and always have only one phonetic
reading (e.g. [tokei], clock). Therefore, reading
of Kana words inevitably involves sequential
letter-byletter or character-by-character reading, although once
the words become familiar, they can be read
letter-byletter or as whole words (discussed later). Due to the
use of these dual systems, alexia in Japan can present
as dissociative reading disturbances between Kanji and
]. For example, Kanji reading is selectively
impaired in alexia with agraphia [
] or pure
] caused by a lesion in the fusiform and
inferior temporal gyri (posterior inferior temporal area;
Area 37), whereas Kana reading is believed to be more
disturbed in alexia with agraphia caused by a lesion in
the angular gyrus [
Alexia with agraphia for Kanji is defined as reading
and writing impairment that is predominantly disturbed
for Kanji. In a literature review, Kanji reading varied
from 8 to 91% correct, whereas Kana reading was 75%
correct or greater [
]. In some patients, alexia
improved to a normal range and agraphia alone remained.
In this sense, it is called pure agraphia for Kanji [
Alexia with agraphia for Kanji from a posterior
inferior temporal cortex lesion is said to parallel lexical
agraphia in European countries [
], because lexical
agraphia is defined as agraphia for irregular words [
and Kanji characters are comparable to
orthographically irregular or ambiguous words [
] (this view is
open to question, see Discussion). It remains unknown
whether alexia with agraphia for Kanji [
agraphia for Kanji [
] and lexical agraphia [
equivalent. Based on the fact that they all arise from
Area 37 insult, it is suggested that they share the same
underlying mechanism. Kana reading is not or less
disturbed in this type of alexia. However, some
patients read Kana more poorly than Kanji with a
similar lesion [
]. It was argued that when Kana
reading impairment is more pronounced, the lesion
extended from Area 37 posteriorly to the lateral occipital
Conversely, in alexia with agraphia from an angular
gyrus lesion, a patient with an infarction limited to the
angular gyrus did not show alexia [
]. We claimed
that alexic symptoms in “angular” alexia with agraphia
may be the result of lesion extension to the
posterior occipital gyri [
], damage to which causes pure
alexia selectively impaired for Kana [
below). Kleist [
] first attributed the alexic symptom
in alexia with agraphia to lesion extension from the
angular gyrus to the middle occipital gyrus, immediately
posterior to the angular gyrus.
Letter-by-letter reading in pure alexia has rarely been
described in Japan. This is probably because there is
no such a compensatory strategy available as spelling
the word aloud in the Japanese language. However,
reading of Kana, which essentially involves the
sequential letter-by-letter process (described above),
becomes slow and laborious. Letter-by-letter reading,
kinesthetic facilitation and inability to read even what
the patient just wrote have been regarded as hallmarks
of pure alexia. In addition, pure alexia in Japan is
known to impair Kanji reading and Kana reading to
varying degrees [
]. This variety of reading
between Kanji and Kana is observed in both classical type
pure alexia (with a splenium lesion) and non-classical
type pure alexia (without a splenium lesion) [
some patients with non-classical type pure alexia, Kana
reading is more disturbed than Kanji reading [
However, reading impairment limited to Kana has not
been reported. We recently reported patients with pure
alexia for both Kanji and Kana  and pure alexia
for Kana only [
]. Pure alexia for Kanji and Kana
showed damage to the fusiform gyrus and lateral
occipital gyri, whereas pure alexia for Kana showed damage
to the posterior occipital areas mainly involving the
inferior occipital/fusiform gyri (Area 18/19). Since the
patient with pure alexia from the fusiform gyrus lesion
showed slight agraphia for Kanji due to impaired
character recall and a patient with alexia with agraphia from
a more lateral fusiform/inferior temporal gyri lesion
showed similar but severer agraphia, we hypothesized
that pure alexia for Kanji and Kana occurred when the
fusiform gyrus was disconnected from the posterior
inferior temporal area (lateral fusiform/inferior temporal
gyri), where visual images of words were thought to be
]. Pure alexia for Kana from a posterior
occipital cortex lesion cannot be explained by this view.
It was suggested that visual images of Kana are widely
distributed in the ventral and lateral occipital gyri [
It was also suggested that there is functional
specialization in the left occipital and occipitotemporal areas for
reading Kanji and Kana; the posterior inferior temporal
area for Kanji and the posterior occipital gyri for Kana.
In the present study, the reading ability of three
patients with alexia with/without agraphia was examined
further using Kanji words, Kana words and Kana
nonwords. The study investigated the correlation of
lesions in these patients with the activated sites shown in
our previous PET studies [
] and proposed
an anatomically-based model of reading that accounts
for pure alexia from different lesions and alexia with
agraphia due to a posterior inferior temporal gyri lesion.
Three patients with alexia underwent a reading test.
The patient profiles are as follows. Patient 1 (pure
alexia for Kanji and Kana) [
]: a 73-year-old,
righthanded man had a cerebral infarction in the left
lingual gyrus in May 1995, although he was not aware
of any visual field defect. In April 1996 he sustained
a second stroke involving the left fusiform and
lateral occipital gyri, after which he could no longer read
any Kana and certain Kanji symbols. He read slowly
and with difficulty even words that he had just
written. A neurological examination showed right upper
homonymous quadrantanopsia. Quantitative
evaluation with the basic 100 Kanji (one-character words) and
the corresponding Kana (Kana transcription of Kanji
] two months after the second stroke revealed
that he read 98% of Kanji and 97% of Kana correctly,
although he spent more than five times longer in reading
compared with normal controls.
Patient 2 (pure alexia for Kana) [
]: a 77-year-old,
right-handed man became aware of a narrowed visual
field and later noticed difficulty in reading Kana
after a cerebral hemorrhage under the left posterior
occipital cortices, mainly affecting the inferior
occipital/fusiform gyri in March 1998. He even had difficulty
reading sentences written by himself. A neurological
examination showed right lower homonymous
quadrantanopsia. He read Kana words character by
character, and spent more time reading five-character Kana
words than three-character Kana words (word length
effect). Quantitative evaluation with the 100 Kanji and
Kana described above two months after onset revealed
that he read 99% of Kanji and 83% of Kana correctly,
requiring 15 times longer than normal for Kana
reading. He also showed a minimal deficit in
discriminating between circles and ovals or between squares and
rectangles of a similar size.
Patient 3 (alexia with agraphia for Kanji) [
71-year-old right-handed man suddenly realized that he
could not remember the names of objects and could not
read newspapers or write anything but his own name,
following a cerebral hemorrhage under the left lateral
fusiform and posterior inferior temporal gyri in June
1991. His visual field was intact. A
neuropsychological examination showed alexia with agraphia
preferentially disturbed for Kanji along with severe anomia.
Quantitative evaluation with 100 Kanji and Kana three
months after onset revealed that he read 20% of Kanji
and 75% of Kana correctly, and correctly wrote from
dictation 4% of Kanji and 59% of Kana. Alexia with
agraphia and anomia persisted at re-evaluation five
years later. Fig. 1 illustrates their lesions drawn on
As a control subject for the visual field defect, patient
4 underwent the same test. This 76-year-old,
righthanded man suffered a first attack of cerebral infarction
in the left medial occipital gyri in December 2000, and
a second infarction in the small area of the right medial
occipital gyri in July 2001. The Goldmann perimetry
and Tokyo Medical College Color Vision Test revealed
that he had right upper homonymous quadrantanopsia
and cerebral achromatopsia, but he did not show alexia
A reading test was provided, consisting of 100
threecharacter Hira-kana words (e.g. [kisoku], rule),
the corresponding two character Kanji words (e.g.
[kisoku], rule), and 100 three-character Hira-kana
nonwords (e.g. [kihise]). The Kana words were
chosen from those with higher familiarity based on how
often the subject had seen, heard or used the word (above
3.50, assessed with a five-point rating scale, range from
0.00 to 4.96) [
]. The Kana nonwords were made
by combining Kana symbols that have no association
with each other [
]. All Kana word and Kana nonword
materials were included among those used in our PET
reading studies (100 out of 240 word or nonword
materials were selected) [
]. The mean
familiarity value of Kanji words assessed with a seven-point
rating scale (range from 1.031 to 6.812) in a recent
research was 6.098 . Patient 2 was further given the
same test and an additional reading test of 100
threecharacter Kana word with low familiarity (range
between 1.50 and 1.99 in the five-point rating scale, above
described) at three years post-onset. Patient 3 was also
given another set of Kana nonword reading test two
Patients’ oral responses and the time spent in
reading were recorded. Errors were classified into
nonresponse, visual, phonological, and semantic. In the
English language based studies, visual errors have been
tightly defined as responses in which there is at least
a 50% overlap of the letters between the target and
]. These criteria, however, do not apply to
Japanese script, in which a visual error occurs within
one character. Errors were regarded as visual when
they had the same component as the target character and
thus resembled it visually, e.g. ([tokai], city) →
([tsugou], convenience). In Kanji, semantic and visual
errors are sometimes difficult to distinguish, whereas in
Kana, visual and phonological errors are sometimes
difficult to distinguish. These errors were labeled as
“semantic and/or visual” or “phonological and/or visual,”
according to the English classification [
examples, see footnote of Table 2). In this regard, almost all
phonological errors in Kana are visually similar to the
target word (at least 50% overlap of the characters), e.g.
([shikai], chairman) → ([shikaku], square),
where two of the three characters are the same. These
were not classified into visual errors but phonological
errors, because visual errors take place at a character
level, as indicated above. When a character in a word
was changed into another character visually similar to
the character, it was classified as phonological and/or
visual errors, e.g. ([ninki], popularity) →
([konki], patience). The present phonological errors
probably correspond not only to phonemic paralexia
errors but to visual and derivational errors in European
A patient was regarded as impaired in reading, when
the score was greater than 2 SD below the normal mean.
If he had a visual field defect and read materials more
than two times longer than the control patient with
quadrantanopsia (patient 4), he still was regarded as
impaired, irrespective of the score.
∗Values are % correct (and time spent in the task; correct responses with kinesthetic reading). The fraction denotes the number of correct
responses versus the total attempts at kinesthetic reading, e.g. 5/8 means that five were correct for all eight kinesthetic reading trials.
∗∗In patient 2, Kana nonword reading was examined two weeks after the Kanji word reading and Kana word reading tests.
∗∗∗In another set of Kana nonword reading test, patient 3 got the score of 67/100 in six minutes two years later.
aNormal controls: 10 men and 1 woman, ages 61 to 78, mean 68 years old, senior high school graduate normal volunteers who had no past
history of neurological disorders [
bKana word reading was more impaired than Kanji word reading.
Abbreviations. M, Man; RU, Right upper quandrantanopsia; RL, Right lower quadrantanopsia; Fu, Fusiform gyrus; Post O, Posterior occipital
gyri; Inf T, Inferior temporal gyrus; Med O, Medial occipital gyri.
Patient 1 (pure alexia for Kanji and Kana caused by a
lesion in the medial fusiform and lateral occipital gyri)
underwent the test two months after onset, when he
became able to read newspapers. At this time, he read
Kanji words more slowly than the control subject with
quadrantanopsia (Table 1), though the reading time did
not exceed two-fold the control patient’s time. He
read Kana nonwords significantly more poorly than
Kana words (p < 0.001, by Fisher’s exact method),
but read Kana nonwords as fast as Kana words. All
his reading errors were phonological ones (phonemic
paralexia; Table 2); he misread one or two characters
in a three-character Kana nonword, some of the errors
apparently being due to visual similarity (phonological
and/or visual error; e.g. [incorrect] for [correct]).
Patient 2 (pure alexia or letter-by-letter reading
caused by a lesion in the posterior occipital gyri)
showed almost selective impairment of Kana reading
(p = 0.0026, between Kanji words and Kana words
by Fisher’s exact method), although Kanji reading was
slightly impaired. He read Kana nonwords more poorly
than Kana words, but not significantly. Time for
reading Kanji was within the normal range or slightly longer
than that of the control patient. Most Kana reading
errors were phonological and phonological and/or
visual ones. In the re-examination with the additional
reading test at three years post-onset, he still read Kana
words and nonwords character by character. The scores
were 99/100 for Kanji (time for reading, 3 min), 99/100
for Kana words (5 min), 97/100 for Kana words with
low familiarity (5 min), 91/100 for Kana nonwords
(5 min), suggesting a familiarity effect in reading
(familiar words are read better than unfamiliar words).
Patient 3 (alexia with agraphia for Kanji caused
by a lesion in the lateral fusiform and inferior
temporal gyri) exhibited severe reading impairments of
Kanji words with relative sparing of Kana word reading
(p < 0.0001 by Fisher’s exact method). However, he
read Kana nonwords markedly more poorly than Kana
words (p < 0.0001 by Fisher’s exact method), although
he read Kana nonwords as fast as Kana words. Most
Kanji reading errors were non- or partial responses
(impaired word recall) and there was only one semantic
error. Conversely, most Kana reading errors were
phonological and phonological and/or visual ones.
First, how the Japanese writing system is related
to European languages is briefly described.
Phonologically, Kana symbols parallel European
consonantvowel syllables or mora in the sense that they develop
one-to-one character-to-sound correspondence.
Orthographically, Kana characters correspond to European
letters. Kana character strings are regular, whether they
are words or nonwords, since there is no pronunciation
ambiguity in translating Kana characters to their
corresponding sounds. Thus, Kana words are comparable
to regular words, and Kana nonwords are comparable
to regular nonwords (pseudowords) [
single Kanji characters correspond to mora too, but they
are irregular, because there is nearly no
character-tosound correspondence. However, Kanji words,
consisting of two or more Kanji characters, have some subtle
regularities (or consistencies, according to the
connectionist terminology) [
]. Therefore, strictly speaking,
Kanji words are comparable to real words (regular and
Next, the semiological features of the alexic patients
are discussed. Then, anatomical substrates of alexia
and a modified dual-route model for reading are
proposed to show how these reading impairments are
explained with this model.
4.1. Neuropsychological considerations
Kana nonword reading was impaired in all three
patients, even when Kana word reading seemed to be
preserved (patients 1 and 3). Single Kana
character reading was also disturbed during the course in
all patients [
]. These findings suggested that
widespread areas in the fusiform (Areas 19 and 37),
inferior temporal and lateral occipital gyri were recruited
in reading Kana characters (not specific for Kana
nonwords). It is also suggested that mere comparison
between Kanji words and Kana words is not enough to
demonstrate dissociation between two scripts, which
has been overlooked in the previous studies.
Prominent Kana nonword reading impairment and
deficient Kana character identification are also
observed in phonological dyslexia [
], in which
nonword reading is selectively impaired. In particular,
patient 3 made a large number of nonword reading errors,
which is attributable to reduced activation of
phonological representations . Thus, the present results
suggest that pure alexia and alexia with agraphia should
be differentiated from phonological dyslexia, and vice
versa. The dyslexic symptom of the present patients
is different from phonological dyslexia in that they
read Kana nonwords as fast as Kana words (Table 1).
In contrast, a patient with phonological dyslexia [
spent more time reading Kana nonwords than Kana
words. This difference in reaction time for Kana
nonwords suggests that in the present patients, impaired
character identification determined the rate of reading,
whereas this was not the case in phonological dyslexia.
Therefore, the present patients’ difficulty reading
nonwords was probably derived from impaired recognition
of Kana symbols. When patient 3 was given another
set of Kana nonword reading test two years later, the
difference between Kana word and nonword reading
was found to be smaller (see footnote of Table 1).
Impairment of character identification was not
evident in Kana word reading, probably because the
patients used lexical (orthographic, phonological or
semantic) help or “lexical capture” [
] in reading.
Lexical capture is a lexical analogy strategy to read
unfamiliar words or nonwords with reference to
lexical knowledge, orthographic, phonological or
semantic . Namely, even if they had difficulty identifying
one character in a word, they could guess the character
from the context. In fact, patient 1 reported that he
used a semantic strategy while reading. Probably the
same mechanism worked in patients 2 and 3, which was
reflected in their performances in reading Kana words
better than Kana nonwords.
The presence of pure alexia for Kanji and Kana
(patient 1) and pure alexia for Kana (patient 2) suggests
that pure alexia can be divided into two types; one for
deficient whole-word recognition and letter or
character identification due to a fusiform gyrus lesion
(ventromedial type; Table 3); and the other for deficient
letter or character identification solely from a posterior
occipital gyri lesion (posterior type; Table 3). Patient
1 had both fusiform and posterior occipital cortex
lesions, thus, it remains unclear which lesion affected his
Kana character reading. Letter-by-letter reading may
be more evident in the posterior occipital gyri lesion,
as in patient 2, probably because this region is more
specific for letter or character identification [
According to a dual-route model of reading [
alexia can arise from a deficit in early visual analysis,
parallel access to word forms, word forms themselves,
or some combination of these loci. In the light of this
view, patient 1 had damage to access to word forms,
whereas patient 3 had damage to word forms
themselves that are located in the posterior inferior temporal
]. The difference of deficits between “access
to word forms” and “word forms themselves” is that
in a word-form deficit severe agraphia due to impaired
character recall coexists and kinesthetic reading is less
effective (described in 4.3) whereas in an access deficit
the patient can write a Kanji he cannot read [
Patient 2 had a deficit in character identification.
Letter identification is thought to be included in visual
]. Thus, impaired Kana character
reading in patient 2 can be attributed to damage to the
visual analysis system. Conversely, relatively preserved
Kanji word reading implies that whole-word reading,
which is expected to be more involved in reading of
graphically complex characters such as Kanji, was still
possible in this patient. He had difficulty reading Kana
words, suggesting that Kana word reading depends less
on whole-word recognition than Kanji word reading.
Deficient character identification in contrast to
relatively preserved whole-word reading suggests that there
is a little serial connection from letter/character
identification to word form representations: a process that
links to word forms (orthographic input lexicon) [
is probably not letter identification but an earlier
visual analysis consisting of line and contour detection
of linguistic and nonlinguistic stimuli. Instead,
letter/character identification directly links to
graphemephoneme conversion, because reading a Kana character
aloud inevitably involves letter/character identification
and grapheme-phoneme conversion and it is difficult
to evaluate separately these two processes only with a
reading test. Therefore, we can safely state that patient
2 had damage to the early visual-phonological route.
This view is supported by our PET studies (Fig. 2 [
]) in which the inferior occipital/fusiform gyri (Area
18/19) were specifically activated in Kana word covert
reading, and more extensive area (including the middle
occipital gyrus) was activated in the Kana word reading
aloud task. These gyri probably constitute a
continuous but functionally distinct, visual (inferior occipital)
to phonological (middle occipital), route.
A problem here is that a single Kana character
reading was impaired in any type of alexia from different
lesions (patients 1 to 3). This fact suggests that visual
images of Kana characters are widely distributed in the
ventral and lateral occipital gyri (described in the
introduction) and are used for both phonology
(graphemephoneme conversion) and orthography (whole-word
recognition). Thus, in general letter/character
identification should not be confined to visual analysis.
Furthermore, the inferior occipital/fusiform gyri (Area
18/19) are more specified to identify Kana characters
(patient 2) and constitute a functionally independent
module that is separable from early visual analysis and
links to grapheme-phoneme conversion.
4.2. Neural basis of reading
We conducted PET reading studies using Kanji
words, Kana words and Kana nonwords separately in
different groups (Fig. 2) [
] and found that: (i) in
addition to the posterior superior temporal gyrus, the
basal occipital and occipitotemporal areas (Areas 18,
19 and 37) were activated by a conjunction [
involving Kanji and Kana, suggesting that these areas are
crucial for real word reading; (ii) activity was more
pronounced in Area 37 in Kanji, which was suggested to be
concerned with the orthography of Kanji, in contrast to
greater activation in Areas 18 and 19 in Kana; (iii)
specific activation for a conjunction involving Kana words
and nonwords was located in the middle occipital gyrus
and the deep perisylvian temporoparietal cortex
(Areas 22/21 and 40/22), suggesting that these areas are
engaged in phonological processing of Kana
character sequences; and (iv) Kana nonwords activated more
Alexia Orthographic∗ Visual-phonological∗ Complications References
Pure alexia: ventromedial type** I (Fu)a rt upper quadrantanopsia [
Pure alexia for Kanji and Kana I (Fu)a I (Fu/Inf O)b rt upper quadrantanopsia [
(Common type; pt 1) or rt hemianopsia
Pure alexia for Kana: posterior type I (Fu/Inf O)b rt lower quadrantanopsia [
(Pure alexia for nonwords; pt 2)
Alexia with agraphia for Kanji from PIT I (Fu/Inf T)a anomia [
(Orthographic alexia with agraphia; pt 3)
∗The orthographic pathway (ventral route) proceeds from the primary visual cortex to the inferior temporal gyrus (Area 37) via the fusiform
gyrus (Area 37). The phonological pathway (dorsal route) proceeds from the primary visual cortex to the superior temporal gyrus and inferior
supramarginal gyrus via the inferior and middle occipital gyri (Area 18/19) and deep perisylvian temporoparietal cortex (Areas 22/21 and 40/22).
∗∗The ventromedial type of pure alexia refers to alexia in which whole-word reading is primarily impaired, and letter-by-letter reading is not
so pronounced. The posterior type of pure alexia is identical with letter-by-letter reading in a strict sense, with preserved whole-word reading.
Many cases of pure alexia have both lesions, as in pure alexia for Kanji and Kana.
aArea 37; bArea 18/19.
Abbreviations: I, Impaired; pt, patient; rt, right; PIT, Posterior inferior temporal area; Fu, Fusiform gyrus; Inf T, Inferior temporal gyrus; Inf O,
Inferior occipital gyrus.
widespread areas in the occipital lobe and
occipitotemporal cortex than Kana words.
PET and functional MRI studies from Western
countries also showed similar findings (for review, see Fiez
et al. [
] and Price [
]): (i) ventral occipital and
occipitotemporal cortices, consisting of Areas 18, 19
and 37, were consistently activated by real words,
pseudowords (corresponding to Kana nonwords) and letter
]; (ii) activity of Area 37 was more
pronounced in real words relative to letter strings ,
and in real words relative to geometric shapes [
] or to
a crosshair [
], in contrast to the greater activity of
the inferior occipital gyrus (Area 18/19) in letter strings
relative to geometric shapes  or to a crosshair [
although in some studies Area 37 was equally activated
by pseudowords [
], in pronouncing letters
relative to saying the same word to false fonts , or in
viewing letter strings relative to faces [
], and Area
19 was most activated in viewing real words relative to
a crosshair [
]; (iii) the middle occipital gyrus (Area
18) was specifically activated by pseudowords and
letter strings [
], and the inner temporal cortex at
the superior temporal sulcus (Area 22/21) was also
activated in real word reading [
], whereas the deep
perisylvian cortex under the posterior ramus of the
Sylvian fissure (Area 40/22) was activated in real word
processing relative to viewing of line drawings  or to
letter string processing [
] and pseudoword
processing relative to letter string processing [
] or to word
]; and (iv) pseudoword processing
produced greater activation in the occipital lobe than real
word processing [
]. Overall, these results suggest
that two distinct areas, i.e. the ventral
occipitotemporal cortex (Area 37) and inferior occipital gyrus (Area
18/19), are crucial for reading.
Based on the above findings, we hypothesized a
weighted dual-route model of reading [
] (Fig. 3) that
modifies Iwata’s model about Japanese [
According to Iwata’s model, Kanji are inevitably processed
from the primary visual cortex to Wernicke’s area by
way of the posterior inferior temporal area (semantic
pathway or ventral route), whereas Kana are mainly
processed from the primary visual cortex to Wernicke’s
area by way of the angular gyrus (phonological
pathway or dorsal route). Iwata’s model is along the lines of
the dual-route hypothesis for reading in Western
]. The basic concept is that two
parallel pathways, i.e. lexical (semantic) and nonlexical
(phonological), are involved in reading, and prior to
these pathways, there is a process of visual recognition
of words or letters [
The modified dual-route model is as follows. The
basal occipital (lingual and fusiform gyri, Area 18/19),
fusiform and posterior inferior temporal gyri (Area 37)
constitute a ventral (orthographic) route for reading and
process holistic word recognition that links to
lexicosemantics, whereas the lateral occipital/fusiform gyri
(Area 18/19), deep perisylvian temporoparietal area
(Areas 22/21 and 40/22) and posterior superior
temporal gyrus constitute a dorsal (phonological) route for
reading and process sequential grapheme-to-phoneme
conversion for words. Early visual analysis consisting
of line and contour detection and the subsequent letter
or character identification are performed in the primary
visual cortex and the surrounding visual association
cortices in the lingual, fusiform and lateral occipital
gyri (the inferior occipital/fusiform gyri [orthographic
route] and middle occipital gyrus [phonological route]
are continuous in the lateral occipital gyri [Area 18/19]
and are also included in the visual analysis system).
The phonological lexical information is stored as
neural networks around the end of the phonological
pathway (posterior superior temporal gyrus), whereas the
orthographic lexical information is stored also as
neural networks around the end of the orthographic
pathway (lateral fusiform and inferior temporal gyri) [
]. The posterior superior temporal gyrus and
posterior inferior temporal cortex (Area 37) have a
reciprocal connection, and facilitate both phonological and
orthographic routes in reading (lexical help or lexical
]. Lexico-semantic information is
diffusely stored in widespread areas extending from Area
37 to the anterior part of the temporal lobe 
(semantic storage site in Fig. 3), and Area 37 intermediates
between orthography and lexico-semantics.
One main feature of the present model is that the two
pathways are not parallel; they change their weight of
involvement according to the number of times the word
is seen and recognized. That is, Kana nonword and
unfamiliar word reading requires both routes. However,
as the word is seen and recognized again and again, the
whole-word image and meaning are stored around Area
37, thus the ventral route gains dominance in reading
real words (Kanji and Kana) [
]. This weighted
dualroute hypothesis is mainly supported by the findings
that Kana nonwords activated more widespread areas
in the ventral and lateral occipital gyri, but not Area 37,
than real (Kanji and Kana) words, and that the ventral
occipital and occipitotemporal gyri (Areas 18/19 and
37) were predominantly activated by a conjunction
involving Kanji and Kana (see Fig. 2 and the summaries
(i) and (iv) of our PET studies described above).
In addition, the dorsal posterior occipital gyri
(middle and superior occipital gyri) that were activated in
Kana word reading relative to Kanji word reading were
also activated in Kana reading aloud relative to Kana
covert reading, and Kana word covert reading relative
to fixation control, although the activation was smaller
in covert reading [
]. These facts suggest that
dorsal posterior occipital gyri that play the part of earlier
phonological processing are more recruited in
4.3. Anatomical substrates of alexia
In the following section, three types of alexia are
described in the light of the present dual-route model. In
essence, the two separately activated areas are
responsible for alexia: the fusiform/inferior temporal gyri (Area
37) for alexia with agraphia and the fusiform/inferior
occipital gyri (Area 18/19) for pure alexia for Kana.
Pure alexia for real words results from damage to the
fusiform gyrus, medial to the fusiform/inferior
temporal gyri. Table 3 summarizes alexias and the supposed
lesion sites with references.
4.3.1. Pure alexia: ventromedial type
Damage to the orthographic (ventral) route causes
pure alexia with less pronounced letter-by-letter
], and alexia with agraphia for Kanji [
] or lexical agraphia in Western countries 
Pure alexia occurs when the fusiform gyrus under
the posterior horn at the occipitotemporal area (Area
37; Fig. 1(a)) is damaged [
] and, as a result,
the lateral fusiform/inferior temporal gyri are
disconnected from the medial fusiform gyrus . As
mentioned earlier, visual images of words or orthographic
lexical information are probably stored around lateral
fusiform/inferior temporal gyri (Area 37) [
and widespread areas in the ventral and lateral
occipital gyri are concerned with letter or character
processing. In this type of pure alexia, therefore, both
letter or character identification and whole-word
recognition become poor, although still possible.
Eventually, impairment is evident chiefly in nonword
reading, in which lexical help [
] cannot be expected,
and many reading errors show visual similarity to the
target. Furthermore, letter-by-letter reading is not so
pronounced, since the posterior occipital gyri are more
specialized to recognize letters or Kana characters and
thus the phonological (dorsal) route compensates for
any reading deficit.
4.3.2. Alexia with agraphia for Kanji from a posterior
inferior temporal cortex lesion
Alexia with agraphia for Kanji [
agraphia for Kanji [
] or lexical agraphia in
Western languages [
], occurs when a lesion is located
more laterally in the fusiform and inferior temporal gyri
(posterior inferior temporal area or Area 37) in the
orthographic route, where visual images of words were
suggested to be stored [
]. In this case,
wholeword images of real words (Kanji and Kana) are
damaged. Thus, reading depends on the intact
phonological pathway. As Kana words and Kana nonwords are
also read, although slowly, with the phonological
pathway, Kanji word reading is predominantly disturbed.
Deficient orthography also affects writing; the patients
cannot write, particularly not Kanji words, because of
impaired word recall [
]. In this sense, alexia with
agraphia for Kanji should be designated “orthographic
alexia with agraphia.” In addition, since letters or
characters are also processed in the ventral occipital gyri,
a slight disturbance in letter or character identification
coexists with this alexia, which is markedly observed
in Kana nonword (or pseudoword) reading (patient 3).
Kinesthetic reading is unsuccessful in alexia with
agraphia for Kanji due to a posterior inferior
temporal lesion (Table 1), probably because visual images
of words per se are disrupted, and thus cannot be
]. Also, anomia accompanies this type of
]. However, severer anomia occurs
when the lesion extends forward to the anterior third of
the temporal lobe or medially to the parahippocampal
The cooccurrence of anomia and alexia with agraphia
for Kanji resembles the symptoms of progressive
fluent aphasia [
] or Gogi (word-meaning) aphasia [
that corresponds to semantic dementia [
Western countries. Anomia and surface dyslexia (particular
difficulty in irregular word reading) are the prominent
features of semantic dementia. An essential difference
between progressive Gogi-aphasia or semantic
dementia and alexia with agraphia for Kanji or orthographic
alexia with agraphia is that semantic dementia derives
from loss of semantic memory for words [
damage to the semantic storage site in Fig. 3), whereas
orthographic alexia with agraphia is an impairment of
orthographic lexicon per se. The apparent similarity
of symptoms, i.e. Kanji words with atypical reading
or European irregular words are read or written more
poorly than Kana words or European regular words
is probably due to the overlap of the lesion site: the
posterior inferior temporal cortex (Area 37).
4.3.3. Pure alexia for Kana: Posterior type
Damage to the visual analysis and the earlier stage of
the phonological (dorsal) route impairs letter or
character identification, thus leading to letter-by-letter
reading. As described earlier, letters or characters are
processed widely in the ventral and posterior occipital
cortices, but the posterior occipital gyri are more
specialized to recognize letters or Kana characters [
Therefore, letter-by-letter reading is more pronounced
in this lesion. Conversely, whole-word reading is
possible in the intact orthographic route, thus Kanji
characters, which primarily depend on holistic recognition
for reading, can be processed by this route. If damage
extends to the cuneus or optic radiation, right lower
quadrantanopsia may occur.
Pure alexia for Kana parallels pure alexia for letters
or syllables, thus for regular words and nonwords,
especially for nonwords that are more difficult to read, with
preserved reading of real words of which whole-word
images are available. Indeed, pure alexia showing a
greater impairment for nonwords has been reported in
Western countries in patients whose lesion involved the
posterior occipital gyri [
Many reported patients with letter-by-letter reading
showed the involvement of both the orthographic route
and the visual-phonological route. The essential
lesion lies in the fusiform gyrus under the posterior horn
(Fig. 1(a)) [
], but we should note that in many
cases the lesion extends posteriorly to involve the
lateral occipital gyri (Fig. 1(c)) [
recognition of both individual letters or characters and
wordforms is disrupted, the patient depends on
letter-byletter reading using the deficient phonological route.
Reading is thus slow and laborious. A lesion restricted
to the fusiform gyrus extending posteriorly to involve
the fusiform/inferior occipital gyri is sufficient to
produce letter-by-letter reading, in this case, without visual
field defects [
]. If the lesion involves the
lingual gyrus or optic radiation, right upper
homonymous quadrantanopsia [
] (the present
patient 1) or hemianopsia [
When the lesion affects the lateral fusiform and
inferior temporal gyri, agraphia accompanies alexia
(orthographic alexia with agraphia, 4.3.2).
Most of the reported letter-by-letter reading cases
were non-classical type pure alexia, in particular
preangular alexia without a splenium lesion [
classical spleno-occipital type pure alexia can also cause
letter-by-letter reading [
], if the transcallosal
fibers (splenium or forceps major) interrupt visual
information going from the right hemisphere to the left
fusiform and lateral occipital gyri. With respect to this
point, patient 1 did not show pure alexia until his
second stroke involving the fusiform gyrus in addition to
the first stroke to the lingual gyrus. This finding
suggested that the right homologous area did not
compensate for the function of the left fusiform gyrus in
reading. The inferior portion of the splenium [
conveys visual information that is necessary for word
or letter recognition (but is not specific for language)
from the right hemisphere to the left fusiform gyrus.
Coslett and Saffran [
] stressed the compensatory role
of the right hemisphere in reading. However, the left
fusiform and inferior temporal gyri seemed spared in
all their patients. Therefore, it is possible that reading
improved when the visual information on words was
transmitted to these gyri through recovered inter- or
4.4. Similarities and differences among other models
Several models of reading have been proposed based
on classic neurology [
], connectionism  and
]. Figure 3 illustrates the present model mapped
onto brain surface images. This model is anatomically
based. Therefore, it is easy to correlate lesions with
symptoms. From a neuroanatomical point of view,
the flow of information is no longer depicted with a
box-and-arrow diagram. There is an overlap of
localization between functional units (modules).
Therefore, modules with oval-shaped areas overlapping each
other were delineated. This model resembles the
dualroute model of Ellis and Young [
] or Patterson and
] in that subsequent to orthographic
analysis, two routes, a direct orthographic lexical route and a
sub-lexical route enabling grapheme-phoneme
conversion, are postulated. But letter/character identification
should not be confined to early visual analysis, as
described in 4.1. According to Ellis and Young’s model
or Patterson and Shewell’s model, the orthographic
lexical route is subdivided into a lexical (phonological)
route, in which a whole-word orthographic lexicon
directly accesses a phonological lexicon, and a semantic
route, in which the whole-word orthographic lexicon
is translated to the phonological lexicon via semantics.
In this sense, their model has three routes. This
basic architecture is also expressed in Coltheart et al.’s
dual-route cascaded model [
The present model is different from Ellis and Young’s
or Patterson and Shewell’s mainly in two points. Firstly,
in the present model the phonological lexical
information (phonological input lexicon) is stored around the
end of the phonological route (or sub-lexical route,
according to Ellis and Young’s or Patterson and Shewell’s
terminology): sub-lexical grapheme-phoneme
conversion is performed in the phonological route, and
access to the phonological (input) lexicon results from
sequential grapheme-phoneme conversions, whereas in
their model grapheme-phoneme conversion has no
direct connection with the phonological (input or
output) lexicon, Instead, grapheme-phoneme conversion
has an access to the phonological output lexicon via
the phoneme level (p. 192 of Ellis and Young [
the phonological output lexicon has no backward
connection to the semantic system. Thus, their model
cannot connect grapheme-phoneme conversion with the
semantic system. This means that reading through
grapheme-phoneme conversion does not reach
semantics. In the present model, converted phonological
sequences for a word may go to the inferior supramarginal
gyrus and superior temporal gyrus where the
phonological lexicon is located, and to this point semantics
have an access. If there is no corresponding
phonological lexicon in the superior temporal gyrus, the
phonological information may be temporarily stored in the
supramarginal gyrus [
Secondly, the present model assumes direct
interaction between the orthographic (input) lexicon and the
phonological (input) lexicon and backward connection
from the phonological (input) lexicon to the visual
analysis, whereas their model has no direct interaction
between the two modules or the backward connection.
This means that their model does not depict
phonological lexical capture, although orthographic lexical
capture is represented as a backward arrow from the
orthographic (input) lexicon to the visual analysis.
The present model is also different from the
dualroute model of McCarthy and Warrington [
] in that
two routes do not stem from what they call the
wholeword system but from early visual analysis.
In these two models, letter-by-letter reading is
explained either by a deficient parallel processing of
letters from orthographic analysis to the orthographic
input lexicon [
] or by impairment of the whole-word
], i.e. a disorder of the orthographic route
between visual analysis and the whole-word system
(orthographic lexicon). However, these assumptions
were suggested to be insufficient to explain sequential
letter-by-letter reading [
]. Recently, Friedman and
] also claimed that letter identification is
divided into an explicit serial process and an automatic
parallel process, and that letter-by-letter reading is the
result of disrupted parallel identification of letters. As
the authors noted, this hypothesis alone cannot explain
why letter-by-letter reading takes much longer than
normal reading. In contrast, the present model explains
that letter-by-letter reading occurs using the damaged
visual-phonological pathway (letter identification
followed by grapheme-phoneme conversion) that is
characterized by sequential processing. It is easier for this
model to account for why letter-by-letter reading takes
Namely, both visual analysis (letter identification)
and access to the orthographic input lexicon
(wholeword reading) are impaired in ventromedial type
pure alexia (4.3.1). As a result, the sub-word level
grapheme-phoneme conversion process, of which is
sequential in nature, compensates for reading
impairment. If this process is intact, letter-by-letter reading
will not be prominent. In the case of posterior type
pure alexia (4.3.3), an area specialized for letter
identification is damaged, which directly affects sequential
grapheme-phoneme conversion, thus leading to
pronounced letter-by-letter reading. In addition, in both
types of pure alexia, the orthographic input lexicon
itself is affected to some degree, because letter
identification and whole-word reading are processed in the
areas anatomically close to each other.
One advantage of this model is that it can explain
various degrees of letter-by-letter reading [
depending on the involvement of the visual-phonological route
(posterior occipital gyri). Furthermore, in the present
model, the orthographic lexicon links to or overlaps
with semantics at Area 37 (Fig. 3). Therefore, if this
area (fusiform and inferior temporal gyri) is involved,
symptoms associated with orthography or semantics
may appear. This assumption probably accounts for
many observations in pure alexia such as accompanying
], semantic reading errors [
], categorization of words the patient could not read
and semantic priming effects , or better
recognition of letters in words than in letter strings [
may also explain semantic errors and comprehension of
words the patient could not read (understanding
without phonology) in alexia with agraphia for Kanji [
The author believes that this simple “double-triangle”
structure is enough to explain the mechanism of
The connectionist model proposed by Seidenberg
and McClelland [
] consists of three functional units
that interact with each other: orthographic,
phonological and semantic, with additional units, called hidden
units, mediating between these units. In their model,
however, letter identification and probably whole-word
reading are not expressed, and other models are
required to simulate letter-by-letter reading or
wordlength effect [
]. In addition, trials to simulate both
word-length effect and correct lexical decision have not
been successful to date .
] reconciled the classic neurological model
] with cognitive models [
functional imaging data, and also proposed an
anatomically constrained model. According to this model,
Wernicke’s area (Area 22/21) sustains nonsemantically
mediated speech output, whereas the posterior inferior
temporal cortex is involved in lexical, semantically
mediated speech output. Access to semantics is made in
the angular gyrus and anterior inferior and middle
temporal gyri. This model differs from the present model
mainly in two points: (i) the angular gyrus is engaged
in semantics; and (ii) the site for the function of
Wernicke’s area is the upper bank of the posterior superior
temporal sulcus (Area 22/21). The author’s view is
that: (i) the angular gyrus is less involved in reading;
crucial areas for reading in this vicinity are the middle
occipital gyrus (posterior to the angular gyrus) and the
deep perisylvian temporoparietal junction (Areas 22/21
and 40/22; anterior to the angular gyrus) [
Moreover, an essential region for lexico-semantics is the
anterior part of Area 37 (MNI coordinates: x = −52,
y = −44, z = −18), 10 mm anterior to the maximal
activation locus of Area 37 for reading [
]; and (ii) the
inner temporal cortex (Area 22/21) is not Wernicke’s
area itself, but posterior to Wernicke’s area which is
by definition located in the posterior half or third of
the superior temporal gyrus (Area 22). The supposed
Wernicke’s area (peak activity, x = −60, y = −20,
z = 6 in a conjunction involving Kanji and Kana) and
the inner temporal cortex at the superior temporal
sulcus were simultaneously activated in our PET reading
]. It is suggested that the inner temporal
cortex (Area 22/21) provides access to the phonological
lexicon that is distributed around the posterior superior
5. Concluding remarks
Visual perception was examined in detail only to
patient 2. This patient had a minimal deficit in
discriminating between two shapes of a similar size, as
described. Based on the fact that the impairment
was limited to minute visual shape discrimination, we
thought that letter/character forms themselves were
]. But it was also possible that this impaired
early visual analysis affected letter/character
identification more or less. Further study is required to elucidate
the role of early visual analysis in reading.
I am grateful to Dr. Toru Mannen, Mitsui Memorial
Hospital, for his support and encouragement.
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