1. hobbies and interests
2. reading

Neuropsychologia, Vol,
~
Pergamon
PU: S0028 3932(97)00032 8
35. No. 8, pp. 11175 1085. 1997
i: 1997 Elsevier Science Ltd. All rights reserved
Printed in Grea! Britain
1/028 3932/97 $17.00+0.00
Lexical and semantic processing in the absence of
word reading: Evidence from neglect dyslexia
ELISABETTA LADAVAS,*?CARLO UMILTA~ and DANIELA MAPELLI+§
*Dipartimento di Psicologia, Universitfi di Bologna, Bologna, Italy; ~Dipartimento di Psicologia Generale, UniversitS, di Padova,
Padova, Italy; §Ospedale 'I Fraticini', Firenze, Italy
(Received 15 Januw:v 1996; accepted 24 January 1997)
Abstract--Nine patients with left-sided neglect and nine matched control patients performed three tasks on horizontal (either normal
or mirror-reversed) letter strings. The tasks were: reading aloud, making a lexical decision (word vs non-word), and making a
semantic decision (living vs non-living item). Relative to controls, neglect patients performed very poorly in the reading task, whereas
they performed nearly normally in the lexical and semantic tasks. This was considered to be a dissociation between direct tasks,
rather than a dissociation between explicit and implicit knowledge. The explanation offered for the dissociation is in terms of both
a dual-route model for reading aloud and a degraded representation of the letter string. ~i~,, 1997 Elsevier Science Ltd
Key Words: neglect dyslexia; visual attention; lexical/semantic access; reading routes.
Introduction
a patient with left visual neglect. The patient could not
read aloud words presented in the left hemifield, nor
judge their lexical status or semantic content. He could
not even detect the presence of strings of letters in that
hemifield. However, response to a word in the right visual
field was faster when the word was preceded by a brief
presentation of an associated word in the neglected left
hemifield. In other words, he indirectly showed associative priming caused by words presented in the neglected
hemifield, even though he was unable directly to process
any attributes of the stimuli in that same hemifield.
Berti et al. [5] documented this type of dissociation in
a patient with neglect dyslexia. In reading regular words
and color words (i.e. a direct reading task), the patient
made the usual pattern of neglect errors on the left side.
However, when asked to name the colors in which color
words were written (i.e. a Stroop-like task that indirectly
tests reading), naming time was found to be affected by
the meaning of those words he was not able to read
correctly.
In the above examples, the use of the term 'implicit"
(or 'covert') is appropriate because it refers to the nature
of the processing that is tapped by indirect tasks. The use
of this term is instead inappropriate when it refers to
tasks in which the experimental procedure implies direct,
explicit judgements, rather than refering to the type of
processing [27, 31, 43].
Several examples of dissociation between direct tasks
can be found in the literature on neglect. Volpe et al. [39]
Much current neuropsychological research concerns
demonstrations of 'unconscious', 'implicit' or 'covert'
information processing. These terms are all used to
denote cases where information processing appears to
proceed more or less normally, despite the absence of
awareness of the results of this processing (see, e.g.
reviews in [27] and [38]).
Although the essence of m a n y of these experiments is
the indirectness of the testing procedure, an important
distinction should be made between types of task and
types of process (e.g. [27, 31, 43]). The use of terms like
'covert' or 'implicit' is better reserved to refer to the
nature of the processinq. In contrast, to characterise tasks,
the term 'indirect' is used. A direct task directly enquires
about a given ability, and performance is dependent on
that ability. In an indirect task, assessment of the ability
in question is incidental and the task ostensibly measures
something else.
In the case of neglect dyslexia, implicit knowledge was
shown through indirect testing by Lfidavas et al. [20], for
t Address for correspondence: Dipartimento di Psicologia,
Universitfi di Bologna, Viale Berti-Pichat, 5, 40127 Bologna,
Italy; tel.: 39 51 242030; fax: 39 51 243086; e-mail: ladavas(a:
psibo.unibo.it.
§? Daniela Mapelli is now at the Dipartimento di Psicologia,
Universitfi di Trieste.
1075
1076
E. Lfidavas et al./Lexical and semantic processing in neglect dyslexia
tested patients with extinction with pairs of visual stimuli
(i.e. drawings of common objects or threeqetter words),
one in each hemifield. On each trial, the patients were
required to perform two direct tasks, that is to name the
stimuli and to judge whether they were same or different.
The patients performed poorly in naming left-visual-field
stimuli, but performed much above chance (between 88 %
and 100% correct) in the same~different matching task.
This outcome is interesting because performing the samedifferent task no doubt requires processing left-sided
stimuli, which the patients were unable to name.
However, it is important to point out that both tasks, the
one in which the patients failed (naming) and the one
in which the patients performed correctly (matching),
required a direct response. In contrast, in the studies by
Berti et al. [5] and Lfidavas et al. [23] the direct response
was modulated by information that was not directly
assessed.
The dissociation between direct identification of leftvisual-field stimuli and cross-field same-different matching was replicated by several authors who studied neglect (see [12], for review). For example, Berti et al.'s study
[4] aimed to determine the level of processing to which
extinguished stimuli were encoded. They also used pairs
of pictures that were physically different but depicted
either the same objects from different views, or different
exemplars of objects belonging to the same category. The
patient performed nearly correctly in matching stimuli
across fields, even though the stimulus on the left could
not be recognised. These results showed that the extinguished stimuli may be coded at least at the category
level. Marshall and Halligan [26] reported a patient with
neglect, who showed a consistent preference for a picture
of a normal house over a picture of the same house with
flames coming from the left side, in spite of her inability
to say whether the two stimuli were the same or different.
The authors proposed that neglect stimuli are processed
at least to the degree that they can evoke a preference
response.
Up to now, however, a dissociation between two direct
tasks has not be documented for neglect dyslexia, even
though it might be expected on the basis of what is known
about this syndrome. Patients with neglect dyslexia (see,
e.g. [29]) typically make errors in reading the left side
(i.e. the beginning) of words and non-words after right
parietal lesion. They omit some of the letters or insert
letters that are not present. More often, however, they
substitute some or all of the letters on the left side. Interestingly, often the number of erroneously substituted letters matches the number of letters actually present in the
letter string (also, see [1 l, 40]). This finding shows that
the patient has some knowledge about the letters present
on the left side, Perhaps on the left there is an impaired
visuo-spatial representation that conveys sufficient information about word length. The fact that errors tend to
be more numerous for non-words than for words (also
see [2, 3]) seems to suggest that lexical information, too,
may in part be preserved in neglect dyslexia.
The aim of the present study was to document the
dissociation between direct tasks in the case of neglect
dyslexia. A group of dyslexic patients were presented with
a letter string and they were asked to perform three tasks,
that is to read aloud the letter string, to judge its lexical
status (word vs non-word), and (if it was a word) to judge
its semantic category (living vs non-living). Every task
required a direct response, but, as will be seen, dissociations emerged. These were because the patients were
able to classify correctly as words or non-words and to
denote as living or non-living items, letter strings that
they could not read.
Basically, three explanations have been offered for the
dissociation between explicit and implicit processing [12,
32, 42]. The first is that an information processing system
is intact but has been disconnected from other brain
systems necessary for showing the type of explicit recognition tapped by direct tasks. The second proposes that
there may be two brain systems capable of processing the
relevant information, only one of which, however, can
mediate explicit recognition through direct tasks. The
third explanation is that implicit recognition reflects the
residual processing capabilities of a partially damaged
brain system. The lower quality information conveyed by
the damaged system is enough for supporting performance in indirect tasks but not for supporting performance in direct tasks.
When the dissociation occurs between two direct tasks,
the explanation that invokes the disconnection of an
intact system from another system (or other systems) that
supports performance in direct tasks is of course not
applicable, both tasks being direct in nature. The explanation that invokes two independent systems is applicable, on condition, however, that it is modified by
proposing that both systems can support performance in
direct tasks, even though only one of them mediates
explicit recognition. The third explanation (that is the one
based on the degraded input from a partially damaged
system) is very easily applicable. One has only to add that
the degraded information is sufficient for executing the
direct task in which the patient performs correctly, but is
insufficient for executing the direct task in which the
patient fails.
In the experiment to be described here, words and
non-words were presented horizontally, either normally
arranged or mirror-reversed. This was done for testing a
proposal by Caramazza and Hillis [6, 7]. They reported
that in some cases neglect affects the highest internal
representation of a word, which, in their view, is always
canonical, that is horizontal and arranged from left to
right, irrespective of how the word is presented.
Method
Subjects"
Two groups selected from the inpatient population of the 'I
Fraticini' Hospital in Florence were tested: an experimental and
E. Lfidavas et al./Lexical and semantic processing in neglect dyslexia
1077
Table 1. Characteristics of the neglect patients (PI P9) and control patients (CI-C9).
For the cancellation tests the number of correct responses are reported. The highest
score is 51 for the letters and 17 for the bells. R = right hemisphere; D = diencephalon:
F = frontal lobe; P = parietal lobe: T = temporal lobe
Cancellation tests
Case
Sex/Age
P1
P2
P3
P4
P5
P6
P7
P8
P9
C1
C2
C3
C4
C5
C6
C7
C8
C9
M,68
M,74
F,71
F,88
M,77
F,69
F,53
F,72
M,67
M,65
M,70
F,80
M,71
M,75
M,66
M,80
F,55
F,67
Education
(yrs)
Onset
of Illness
(mths)
Locus
lesion
17
17
8
13
8
13
5
8
5
5
13
8
8
5
17
13
8
8
3
14
2
2
9
2
4
4
3
5
3
14
2
3
2
2
4
3
RTD
RD
RPT
RFP
RFPT
RFD
RPTD
RTD
RPD
RT
RPD
RD
RD
RD
RFTP
RD
RPT
RTP
a control group. The experimental group consisted of nine
neurological patients without visual field deficit,t each with a
severe left visual neglect, neglect dyslexia for words and nonwords, and hemiplegia or severe hemiparesis contralateral to
the lesion. The nine patients were selected from a larger population of 34 patients with severe left visual neglect, without
intellectual and psychiatric disorders. The characteristics of
each subject group are outlined in Table 1.
The control group consisted of nine inpatients with right
hemispheric lesions without visual neglect or visual field deficits.
The presence/absence of horizontal visual neglect was
assessed by a number of tests. In the current study, only some
of them are mentioned. Others, such as drawing from memory,
drawing from a sample, and reading sentences, will not be
reported. For the present purposes, the relevant tests were: (1)
to cross out ' H ' s in a structured array of letters [10]; (2) to cross
out lines of a given orientation that were displayed among lines
of many different orientations [1]; and (3) to cross out bells in
a display of drawings of several objects [15]. Neglect patients
who omitted more than 60% of the stimuli on the left in each
test were included in the experimental group and they were then
tested for neglect dyslexia.
Few patients with visual neglect showed reading errors for
words, whereas most of them manifested the deficit for nonwords. Because the aim of the present study was to explore the
t In the present study patients with visual field deficits were
not included in the experimental group because the presence of
visual sensory deficits renders the interpretation of the results
unclear. When these patients are tested, a lack of response for
stimuli presented on the contralesional space may be due to a
visual sensory deficits or to a specific impairment in spatial
representation. Therefore, we believe that, in order to study
spatial representational disorders, it is better to test patients
without sensory deficits, although it is true that most of the
neglect patients, but not all, have visual field deficits.
.
Letters
. . . .
L
R
0
I~
I~
1
II
38
2I
0
II
45
51
51
51
50
46
45
47
49
11
15
6
16
6
45
41
5
6
46
51
50
51
51
46
47
48
48
Bells
.
.
k
R
0
0
0
1
0
10
0
0
0
7
7
6
7
6
7
6
7
7
4
5
5
12
5
16
10
9
5
17
17
16
17
17
16
12
16
17
degree of preservation of lexical and semantic access in neglect
patients, the investigation was confined only to patients who
showed neglect dyslexia for words. Patients who made more
than 20% of errors of the neglect dyslexia type on both words
and non-words were then studied. Control patients who omitted
less than 5% of the stimuli on either side were included in the
control g r o u p
Stimulus and procedure
The stimuli were 78 letter strings, the length of which could
be 7 letters (6 stimuli), 8 letters ( 16 stimuli), 9 letters (22 stimuli),
10 letters (22 stimuli), or I 1 letters (12 stimuli). Each letter was
printed on upper case Palatino style (18pt). Half of the stimuli
were Italian words (39 stimuli) and the other half (39 stimuli)
were legal non-words obtained by substituting one (6 stimuli)
or two (33 stimuli) vowels. For the non-words, the substituted
vowels were equally located on the left and on the right side of
the stimulus. All the words were concrete and denoted either
living or non-living items (18 and 21, respectively). C o m p o u n d
words were not used. The stimuli, located in the centre of the
page (A4 format), were written horizontally, either normally or
mirror-reversed. Each letter string was presented twice: once in
the normal horizontal orientation, and once in the horizontal
mirror-reversed orientation. They were shown one at the time
by means of a moveable window, that is a window that concealed all the letter strings except the one that was currently
shown to the patient.
In the reading task, the patients were instructed to read the
letter string aloud. In both the lexical and the semantic tasks
they were instructed to make a decision about whether the letter
string was a word or a non-word (lexical decision) and whether
the word denoted a living or a non-living item (semantic
decision). Each patient attended three experimental sessions in
1078
E. Lfidavas et al./Lexical and semantic processing in neglect dyslexia
3 consecutive days.t Order of task was determined randomly
and independently for each patient.
Before performing the reading task, the patient was explicitly
told that 50% of the letter strings were words and 50% were
non-words, and that half of the stimuli were normal and half
were mirror-reversed. Before performing the semantic task, the
patient was told that only words would be shown, and that half
denoted living items and half non-living items. The patient was
also told that there was no time pressure for providing the
response.
,oo
N e g l e c t patients
90
W = Word
NW = Non-word
80
L = Living
70
NL = Non-living
60
50
40
Results
In the analyses of variance (ANOVAs) to be reported
below, the dependent variable was accuracy, as indexed
by error rate. In the case of the reading task, omitting or
misreading one or more letters was considered to be an
error for the whole letter string. For the lexical and semantic tasks, responses indicating an incorrect categorisation were considered errors.
The probability that a word or a non-word is read
completely without error (i.e. without omitting or misreading a single letter) is much lower than the 50% chance
rate that applies to the lexical and semantic tasks. It must
be pointed out, however, that the confounding between
performance at chance level and type of task would be
very damaging if the patients had the tendency to misread
single letters in the string. Instead, our patients' errors
were much more often omissions than substitutions (91%
vs 9% overall, for either words or non-words). Substitution errors were those in which the patients produced
the same number of letters as in the letter string but
erroneously substituted one or more letters. Thus, considering the different distribution of omissions and substitutions, it does not seem likely that they tried to guess
the letter they could not read. Perhaps, the fact that
errorless reading was less likely than making a correct
lexical decision or a correct semantic decision might
explain why controls were more accurate in the lexical
and semantic tasks than in the reading task (see results
below).
Two A N O V A s were performed on errors (also see Figs
1 and 2, and Table 2). All factors were within-subjects
factors, except for the one concerning group.
A first A N O V A was performed only on words. In it the
factors were: group (patients vs controls), task (reading,
lexical decisions or semantic decision), and stimulus
orientation (normal vs mirror-reversed). The Bonferroni
correction for the number of sources of variability yielded
alpha--0.007. The main effects of group, task, and the
interaction group x task, were significant: [F(I, 16)= 99.3,
P<0.0001, F(2,32)= 119.2, P<0.0001], and [F(2,32)=
100.5, P < 0.0001 ], respectively.
Errors were more numerous for patients than for con-
30
20
10
0
NW
W
NW
L e x i c a l task
L
NL
S e m a n t i c task
Fig. 1. Percentage of errors committed by the neglect patients in
the three tasks (reading, lexical decision, and semantic decision).
trois (29.5% vs 4.3%), and for the reading than for either
the lexical or the semantic task (36.9% vs 8.6% and
5.3%). The interaction showed that the difference in accuracy between patients and controls was much greater in
the reading task (67.9% vs 5.9% errors, P<0.001) than
in the lexical task (11.9% vs 5.3%, n.s.) or the semantic
task (8.9 % vs 1.8 %, P < 0.01 ). Normally oriented words
produced fewer errors than mirror-reversed words in
reading, lexical and semantic tasks both in neglect patients (65.5 vs 70.3, 6.5 vs 17.3, 5.7 vs 12.1, respectively)
and normal subjects (4.5 vs 7.4, 4.2 vs 6.5, 1.1 vs 2.6,
respectively), However, none of the sources that included
the factor stimulus orientation was significant.
The second A N O V A was performed on responses to
both words and non-words. The inclusion of non-words
Control patients
100
90
W = Word
80
NW = Non-word
70
L = Living
NL = Non-living
60504030-
10
o
t Subsequently, the patients were tested in additional experimental sessions with the same stimuli arranged vertically. These
data will be reported elsewhere.
W
R e a d i n g task
w
NW
R e a d i n g task
w
NW
L e x i c a l task
L
NL
S e m a n t i c task
Fig. 2. Percentage of errors committed by the control patients in
the three tasks (reading, lexical decision, and semantic decision).
E. L/tdavas et al./Lexical and semantic processing in neglect dyslexia
1079
Table 2. Percentage of errors committed by each neglect patient (P l-P9) in the three tasks (reading:,
lexical decision, and semantic decision)
Reading task
Case
PI
P2
P3
P4
P5
P6
P7
P8
P9
X
Lexical task
Semantic task
Word
Non-word
Word
Non-word
Living
Non-living
64
73
56.3
74.3
84.5
93.5
65.3
43.5
56.4
67.9
93.5
87.1
83.3
93.5
97.4
94.8
74.3
92.3
93.5
89.9
16.6
12.7
3.9
21.7
15.3
17.9
6.3
10.2
2.5
11.9
1.2
I 1.5
12.7
10.2
16.6
25.5
8.9
15.3
7.6
12.2
l1
13.8
2.5
2.7
32
8.3
16.5
24.9
11
13.6
0
7.1
0
0
4.7
7.1
9
9.5
0
4.2
rendered it necessary to eliminate the results for the semantic decision, which concerned only words. The factors
were: group, task (reading vs lexical decision), lexical
status (word vs non-word), and stimulus orientation.
With the Bonferroni correction, alpha---0.003. The main
effects of group [F(1,16)=145.7, P<0.0001], task
[F(1,16) = 694.6,
P<0.0001],
and
lexical
status
[F(1,16)=36.9, P<0.0001] were all significant. Also the
interaction group x task [F(1,16)= 359.8, P < 0.0001] was
significant.
The second analysis showed that the results of the
first one also held true when non-words were included.
Patients made more errors than controls (45.5% vs
9.9%), and more so in the reading task (78.9% vs 15.4%,
P < 0 . 0 0 1 ) than in the lexical task (12% vs 4.5%,
P<0.01). For either group, the reading task proved to
be more difficult than the lexical task (47.1% vs 8.2%
errors). Normally oriented non-words produced fewer
errors than mirror-reversed non-words in the reading
task but not in the lexical task, both in neglect patients
(87.4 vs 92.6, 14.2 vs 10.2) and control subjects (20.8 vs
29, 4.5 vs 2.8). However, none of the sources that included
the factor stimulus orientation was significant.
Another A N O V A was performed in the reading task
to establish whether errors occurred more often on the
left than on the right side of the letter string. Side was
determined with reference to egocentric space for both
normal and mirror-reversed letter strings. Thus, the letters at the begining of the letter string were coded as
being on the left for normal strings and as being on the
right for mirror-reversed strings. In the case of strings
with an uneven number of letters, the central letter was
not considered.
In this ANOVA, the dependent variable was the percentage of omitted or misread letters on each side of
the letter string. The factors were: group, lexical status,
stimulus orientation, and side (left or right). With the
Bonferroni correction, alpha=0.003. The significant
sources that included the factor side were the main effect
side [F(1,16) = 110.50, P < 0.001] and the interaction group x side [F(1,16)= 103.50, P<0.001]. Errors were more
numerous on the left than the right side ~29. 1% vs 5.8%),
but this asymmetry was present in the patient group
(55.7% vs 9.9%) and absent in the control group (2.6%
vs 1.8%).
Neglect patients made more errors on the left than on
the right side in all reading conditions, i.e. when the task
required to read normally oriented words (50.3 vs 5.4),
mirror-reversed words (52.3 vs 12.1), normally oriented
non-words (61.9 vs 7.0) and mirror-reversed non-words
(58.2 vs 15.0). None of the sources including stimulus
orientation was significant.
Controljor guessing and other alternative strategies
The patients performed much better in the lexical and
semantic decisions than in the reading task. An obvious
possibility is that the letters reported in the reading task,
although incomplete and incorrect, were enough for
allowing a good guess about the lexical status and the
semantic category of the letter string. That is to say, the
patients might have used successfully a guessing strategy
based on the outcome of whatever they were able to read.
If this were the case, normal subjects should also be
able to make correct lexical and semantic guesses when
presented with the patients' verbal productions in the
reading task. To control for this possibility, we proceeded
as follows.
The letter strings produced by each patient in the reading task were written on a piece of paper and were presented to four independent judges. Different judges were
used for each patient, for a total of 36 judges. They
were matched to the patients for age, sex and years of
schooling. The controls were told that the letter string
was an error produced by a patient when trying to read
a word (or a non-word) and that the letters produced
were mostly based on the right part of the word (although
they may not be an entirely correct rendering of that part
of the word). They were also given a number of examples.
The task was two-Ibid. In the first session, the judges
were asked to guess whether the letter string belonged to
E. Lfi,davas et al./Lexical and semantic processing in neglect dyslexia
deficit always affects one part of the word, regardless of
the way the letter strings are presented. In the current
study, the deficit might have affected the letters on the
left side for normally arranged words and the letters
on the right side for mirror-reversed words. The results
showed that mirror-reversed stimuli, which are probably
more difficult to be processed, produced more errors than
normally oriented stimuli, although the difference was
never significant and that left-sided errors were frequent
for either normal or mirror-reversed stimuli. The third
ANOVA, in which side (left or right) was included as a
factor, is the relevant one for testing Caramazza and
Hillis's hypothesis. It showed that the errors occurred
always on the left side for either normal or mirrorreversed words. That is to say, neglect affected the egocentric left side of the words, rather than the left side of
their canonical representations. It must be pointed out,
however, that this finding does not confute Caramazza
and Hillis's [6, 7] hypothesis, because in their model neglect can occur at each of three levels of representation,
and that form of neglect dyslexia that affects the egocentric, stimulus-centered, representation is by far the most
frequent one.
The most interesting finding of the present study was
that neglect patients performed much better in the lexical
and semantic tasks than in the reading task. Actually,
they performed very close to controls in the first two
tasks, whereas their performance in the reading task was
grossly impaired. These task-related differences cannot
be attributed to the fact that there was a trend for word
stimuli to produce word responses (either correct or
wrong) and for non-word stimuli to produce non-word
responses (either correct or wrong). In fact, patients produced non-word responses irrespective of the lexical
status of the letter string.
The simplest way to explain the task-related differences
is by making the reasonable assumption that reading is a
much more difficult task than either a lexical or a semantic
decision. This is because the probability of being correct
by adopting a guessing strategies is far lower in reading
than it is in the other two tasks. This interpretation was
addressed in the present study by asking normal controls
to use the patients' responses to make lexical and semantic decisions. Because the controls could not produce
correct lexical and semantic decisions on the basis of
the patients' responses, it was concluded that successful
guessing strategies on the patients' part was unlikely.
One might however argue that the patients have some
partial information and this information may help in the
lexical and semantic tasks but may be insufficient for
reading. Partial information about letters on the left can
interact with later top down levels of processing and may
suffice for performing the lexical semantic tasks but may
be insufficiently precise to allow correct identification of
the individual letters. This would be consistent with a
computational model proposed by Mozer and Behrmann
[28]. The important point is that in the control experiment
aimed at testing the guessing interpretation, normal sub-
1081
jects were shown only the patients' final output, in which
the degraded information on the left was missing. Thus,
there was no basis for the higher t o p - d o w n processes to
clean up degraded information.
Even though the above account is in principle tenable,
we believe it cannot be applied to the performance of the
patients in the present study. Mozer and Behrmann's [28]
model was proposed to explain reading pertbrmance
of patients with mild neglect dyslexia, for whom most of
the information on the left side of the words is still available, though in a degraded form. The patients described
in this study, instead, had a severe neglect dyslexia, as
attested by the fact that in the case of four- to five-syllable
words, they reported only the one or two syllables on
the right side. An interpretation in terms of guessing
strategies, based on the degraded information, in the
lexical and semantic tasks is perhaps applicable to twoto three-syllable words. In contrast, in our data there was
no indication whatsoever that accuracy in the lexical and
semantic tasks depended on word length.
A further indication that a guessing strategy, based on
the available partial information, was not used comes
from the fact that lexical and semantic decisions were
equally accurate for normal and mirror-reversed letter
strings. When the words were mirror-reversed, the letters
that were available at the explicit level belonged to the
beginning of the word. Considering that the stem is the
most important part of a word, guessing should have been
more effective with mirror-reversed than with normally
oriented words. None of the ANOVAs supported this
prediction.
In addition, it should be kept in mind that in the present
study legal non-words were derived from words by substituting one or two vowels. Therefore, non-words were
very similar to real Italian words. If one assumes that
top down processing played a major role in cleaning up
degraded inlbrmation, and considering that the lexicon
contains only words, then the prediction is that the patients should produce more word than non-word incorrect
responses, and incorrect word responses should be similar
to the word from which the non-word was derived. In
contrast, lexicalisation errors were extremely rare (see
Table 4) and the incorrect word responses were of the
omission type.
An anonymous reviewer has suggested another
interpretation that since in the reading task patients were
told to expect word and non-word stimuli, the readingaloud response may follow some kind of silent analysis,
performed on the letter string in order to decide whether
it was a word or a non-word. The implicit lexical decision
about the stimulus might have produced a rapid decay of
the perceptual representation already degraded on the
left side. This, in turn, might have produced reading
errors confined on the left side of the letter string. This
interpretation can be rejected in view of a recent study
by Lfidavas el al. [22] in which it has been shown that
patients wilh neglect dyslexia, showing preservation of
lexical/semantic judgements for words they could not
1082
E. L~davas et al./Lexical and semantic processing in neglect dyslexia
originally read, were able to read the word aloud following the lexical/semantic processing of the word. For
the same reason, Luck et al.'s findings [24] (showing that
words presented during the attentional blink are analysed
to the point of meaning extraction, even though the
extracted meaning cannot be reported 1-2 sec later), are
not relevant for the interpretation of the present results.
After having discarded the simplest interpretations, we
proceed by taking into consideration alternative explanations that are based on the assumption that the present
results reflect a true dissociation between different mechanisms used by patients in the different tasks.
All the three tasks were direct, but performance was
much better in two of them than in the third. What we
have found, therefore, is a dissociation between direct
tasks rather than between implicit and explicit knowledge
(see [27, 31, 43]). A possible explanation of this dissociation might be in terms of the residual processing
capabilities of a partially damaged brain system (e.g.
[12]). In neglect patients, the visual representation of the
letter string is impaired [2, 3]. Consequentely, an inappropriate representation within the visual word-form system might be activated [40]. This faulty access to the
visual word-form system would cause reading errors but
would allow correct lexical and semantic discriminations,
which can be carried out with a weaker or noisier output
from the orthographic system than that required for reading aloud. Note that this account is different from the
one we have discussed, and rejected, above. The latter
was mainly based on the notion that top-down processes
clean up the degraded information and because of that
differently affect the probability of being correct in the
three tasks. The probability of being correct would be
much higher in the lexical and semantic tasks than in the
reading task.
The explanation we are considering now maintains
that a failure to identify or read the letter string is to be
attributed to a decreased level of activation within the
system that normally subserves explicit identification [34].
It can be noted in passing that this view is compatible
with a cascade-type model of reading processes [25].
Weak input from an impaired word-form system could
allow sufficient activation of the corresponding lexical
and semantic representations to activate other representations by spreading activation, but not enough to
inhibit the competing possibilities which an explicit
identification requires. The degraded output of the orthographic system may be sufficient to support the correct
category discrimination without being sufficient for the
identification of the specific item itself. This is similar to
the argument put forward by Farah [12] to explain some
related neglect phenomena, and is essentially analogous
to the explanation given for the performance of some
semantic access and pure alexic patients who can carry
out lexical decisions and perform category judgements at
well above chance levels on words they cannot read aloud
or identify [10, 35, 41].
An alternative interpretation of the dissociation may
be found by making recourse to the classical dual-route
model of reading aloud (e.g. [8, 33]). According to this
model, a written letter string can be read by a non-lexical
phonological route that implies grapheme-to-phoneme
conversion, and by a lexical route that implies direct
access to the mental lexicon through the visual representation of words.
We propose that, due to the neglect deficit, our patients
had a degraded visual representation of the letter string
([2, 3]). The representation was degraded because the
component letters were poorly differentiated or because
their relative order within the string was partly lost ([18,
30]). This degraded representation did not allow correct
reading.
Contrary to usual, errors were of the missed variety,
rather than of the substitution type. A possible explanation for that is that neglect was very severe and did not
allow the processing of the word length, which usually
produces substitution errors. Also, errors were typically
non-words (see Table 4). This can be considered as evidence that in the reading task our patients made use
of the non-lexical phonological route, perhaps because
lexical routes are useless for non-words. The low percentage of lexicalisation errors may be conceived as evidence that lexical routes were seldom used by our patients
when the task required reading aloud. If they had used
the addressed phonology, obtained through the lexical
routes, and considered that non-words differed by just
one or two vowels from real words, one should have
expected to find many lexicalisation errors in response to
non-words. That is, the patients should have read most
non-words as words. This prediction was clearly contradicted by the results (see Table 4). Patients showed a
strong bias to produce non-words in response to either
word or non-word stimuli, although the bias seems
stronger for non-word than word targets. In conclusion,
it would seem likely that our patients used the non-lexical
phonological procedure in the reading task. In contrast,
it would seem that they, when asked to make lexical and
semantic categorisation tasks, made use of the lexical
routes, which could still operate even though the representation of the letter string was degraded.
One question that needs to be addressed is why the
non-lexical phonological route is more affected by neglect
disorders than the lexical routes. It may be possible that
the use of the lexical routes requires, but also leads to, a
broadening of the attentional focus. In contrast, the use
of the phonological route, due to the existence of multiple
perceptual units within the same display, leads to a greater bias to the right by comparison with the single perceptual unit that is the input to the lexical routes.
Evidence in favour of this interpretation comes from
studies that showed that the lexical status of the letter
string influences the distribution of visual attention [13,
36, 37].
The Farah et al.'s study [13] showed that in a letter
colour naming task, neglect patients were more accurate
at naming the colours on the left when the letter string
E. L~tdavas et al./Lexical and semantic processing in neglect dyslexia
was a word than when it was a non-word. In addition,
when the same patients were asked to mark the centre of
a line that was presented underneath the letter string, the
spatial distribution of attention was more symmetrical
for words than for non-words. Sieroff and Posner [37]
showed that, in normal subjects, when attention was cued
to the left or right of foveal-centered letter strings,
responses were greatly biased by the direction of attention
for strings of consonants and not for orthographically
regular words. The authors argued that chunking the
letters within a visual word does not require attention
because a visual word is processed as a single perceptual
item. If a word constitutes a whole, it is not necessary
for attention to scan the component letters. In contrast,
orthographically irregular strings are comprised of many
independent letters, and attention is necessary for scanning them. This reasoning was used by Sieroff et al. [36]
to explain the well-known effect that neglect patients
make fewer errors in reading words as compared to nonwords.
In addition, the notion that the size of attentional focus
depends on task demands is compatible with the results
of many studies on normals, in which it has been shown
that, unlike naming latency [14], latency for semantic
category decisions is unaffected by word length [16], and
with the distinction between object-based and locationbased attentional effects [12, 19], whereby object representations to which attention can be allocated may
include such abstract objects as words, that is the input
to the lexical routes.
In conclusion, two alternative explanations have been
offered to explain the dissociation between reading task
and lexical and semantic categorisation tasks. The first is
analogous to the explanation given for related phenomena in semantic access dyslexia and pure alexic patients,
who can carry out lexical decisions and perform category
judgements at well above chance level on words they
cannot read aloud or identify [9, 17, 35, 41]. The other
explanation is in terms of different reading routes, which
require, but also lead to, different patterns of spatial
attention over the degraded representation of the letter
string. The lexical routes lead to an attentional focus
that encompasses the single perceptual unit, whereas the
phonological route leads to a bias of the attentional focus
to the rightmost position of multiple perceptual units
within the display. The attentional bias may play an
important role in determining the extremely poor performance in the reading aloud task, as has been shown
in many other perceptual tasks [21, 23].
Note that the interpretation based on the dual-route
model differs from the quality of representation account
that was put forward, among others, by Farah [12], which
was discussed above. In Farah's account, neglect is
assumed to result in a poor-quality representation that
provides degraded information to higher level processes.
This poor-quality representation is held to be sufficient
to subserve tasks that require binary decisions (e.g. lexical
decisions. Jiving/non-living judgements, same~different
1083
matchings of letters or objects), but would be insufficient
to subserve multiple-choice naming.
Even though the findings of the current study are no
doubt consistent with both accounts, the two proposals
are logically distinguishable because they make different
predictions (see [22]). The degraded-information account
predicts that performance of neglect patients should
deteriorate as the semantic task becomes more difficult.
In contrast, the dual-route account predicts that the level
of performance in the semantic task should not depend
on the difficulty of the semantic discrimination. This issue
was directly addressed in a recent study by L'fidavas et al.
[22], in which neglect patients performed a living/nonliving semantic decision task, a semantic categorial task,
and a semantic inferential task.
The living/non-living task was identical to the one used
in the present study. In the categorial task, a visual target
word was shown and was followed by two acoustically
presented words, only one of which belonged to the same
category as the visual target. Both, however, belonged to
the broader living or non-living category (e.g. camel:
elephant or fir-tree). The inferential task was very similar
except that the two members of the pair belonged to the
same semantic category, but only one of them was related
to the target by means of a common feature (penguin:
tuxedo or tracksuit). In either the categorial or the inferential task, the patient was asked to make a decision
about which item was more related to the target, The
results showed that performance was normal in every
task, and, in accordance with the prediction of the dualroute hypothesis, it did not depend on the size of the
category that was tapped by each task.
In view of the results of the study by Ladavas et al.
[22], we prefer to explain the findings of the current study
according to the dual-route model, even though, in themselves, they can also be interpreted on the basis of the
poor-quality information hypothesis.
Acknowledgements--We are indebted to Barbara Cosi and Cristina Dazzi for collecting part of the data. E.L. and C.U. were
supported by grants from MURST. C.U. was also supported
by CNR through contract no. 9300752.PF41.
References
1. Albert, M. L. A simple test of visual neglect. Neurology 23, 658-664, 1973.
2. Behrmann, M., Moscovitch, M., Black, S. E. and
Mozer, M. Perceptual and conceptual mechanisms
in neglect: Two contrasting case studies. Brain 113,
1163-1183, 1990.
3. Behrmann, M., Moscovitch, M. and Mozer, M. C.
Directing attention to words and nonwords in normal subjects and in a computational model: Implications for neglect dyslexia. Cognitive Neuropsychology 8, 213-248, 1991.
4. Berti, A.. Allport, A., Driver, J., Dienes, Z., Oxbury,
1084
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
E. Lfidavas et al./Lexical and semantic processing in neglect dyslexia
J. and Oxbury, S. Levels of processing for visual
stimuli in an 'extinguished' field. Neuropsychologia
30, 403-415, 1992.
Berti, A., Frassinetti, F. and Umilt/t, C. Nonconscious reading? Evidence from neglect dyslexia.
Cortex 30, 181-197, 1994.
Caramazza, A. and Hillis, A. E. Spatial representation of words in the brain implied by studies
of a unilateral neglect patient. Nature 346, 267-269,
1990.
Caramazza, A. and Hillis, A. E. Levels of representations, co-ordinate frames, and unilateral
neglect. Cognitive Neuropsychology 7, 391-445, 1990.
Coltheart, M., Cognitive neuropsychology and the
study of reading. In Attention and Performance XI,
ed. M. I. Posner and O. S. M. Marin. Erlbaum,
Hillsdale, NJ, 1985, pp. 3-37.
Coslett H. B. and Saffran E. M., Mechanisms of
implicit reading in alexia. In The Neuropsychology of
High-level Vision, ed. M. J. Farah and G. Ratcliff.
Erlbaum, Hillsdale, N J, 1994.
Diller, L. and Weinberg, J., Hemi-inattention in
rehabilitation: The evolution of a rational remediation program. In Hemi-inattention and Hemispheric Specialization, ed. E. A. Weinstein and R. P.
Friedland. Raven Press, New York, 1977, pp. 63-82.
Ellis, A. W., Flude, B. M. and Young, A. W. 'Neglect
dyslexia' and the early visual processing of letters in
words and nonwords. Cognitive Neuropsychology 4,
439-464, 1987.
Farah, M. J., Visual perception and visual awareness
after brain damage: A tutorial overview. In Attention
and Performance XV, ed. C. Umilth and M. Moscovitch. MIT Press, Cambridge, MA, 1994, pp. 37-75.
Farah, M. J., Wallace, M. A. and Vecera, S. P.,
'What' and 'Where' in visual attention: Evidence
from the neglect syndrome. In Unilateral Neglect:
Clinical and Experimental Studies, ed. I. H. Robertson and J. C. Marshall. Erlbaum, Hillsdale, N J,
1993, pp. 123 136.
Frederiksen, J. R. and Kroll, J. F. Spelling and
sound: Approaches to the internal lexicon. Journal
of Experimental Psychology: Human Perception and
Performance 2, 361-379, 1976.
Gauthier, L,, Dehaut, F. and Joannett, J. The bell
test: A quantitative and qualitative test for visual
neglect. International Journal of Clinical Neuropsychology 11, 49-54, 1989.
Green, D. and Shallice, T. Direct visual access in
reading for meaning. Memory and Cognition 41,753758, 1976.
Hinton, G. E. and Shallice, T. Lesioning an attractor
network: Investigations of acquired dyslexia. Psychological Review 98, 74-95, 1991.
Humphreys, G. W. Besner, D. and Quinlan, P. T.
Orthographic processing in visual word identification. Cognitive Psychology 22, 517-560, 1990.
Humphreys, G. W. and Riddoch, M. J., Interactive
attentional systems and unilateral visual neglect. In
Unilateral Neglect: Clinical and Experimental Studies, ed. I. H. Robertson and J. C. Marshall. Erlbaum,
Hillsdale, N J, 1993, pp. 123 136.
Lhdavas, E., Paladini, R. and Cubelli, R. Implicit
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
associative priming in a patient with left visual
neglect. Neuropsychologia 31, 1307-1320, 1993.
L~idavas, E., Petronio, A. and Umilt~., C. The deployment of attention in the intact field of hemineglect
patients. Cortex 26, 307 317, 1990.
Lhdavas, E., Shallice, T. and Zanella T., Preserved
semantic access in neglect dyslexia. Neuropsychologia
35, 257-270, 1997.
Lfidavas, E., Umilth, C., Ziani, P., Brogi, A. and
Minarini, M. The role of right-side objects in leftside neglect: A dissociation between perceptual and
directional motor neglect. Neuropsychologia 31, 761
773, 1993.
Luck, S. J., Vogel, E. K. and Shapiro, K. L. Word
meanings can be accessed but not reported during
the attentional blink. Nature 383, 616-618, 1996.
McClelland, J. L. and Rumelhart, D. E. An interactive model of context effects in letter perception:
Part 1. An account of basic findings. Psychological
Review 88, 375-407, 1981.
Marshall, J. C. and Halligan, P. W. Blindsight and
insight in visuo-spatial neglect. Nature 336, 766 767,
1988.
Milner, A. D. and Rugg, M. D., The Neuropsychology of Consciousness. Academic Press,
London, 1992.
Mozer, M. and Behrmann, M. Interaction of selective attention and lexical knowledge: A connectionist
account of neglect dyslexia. Journal of Cognitive
Neuroscience 2, 96-123, 1990.
Riddoch, J. Neglect and peripheral dyslexia. Cognitive Neuropsychology 7, 369-389, 1990.
Riddoch, J., Humphreys, G., Cleton, P. and Fery, P.
Interaction of attentional and lexical processes in
neglect dyslexia. Cognitive Neuropsychology 7, 479
517, 1990.
Rugg, M. D., Conscious and unconscious processes
in language and memory--Commentary. In The
Neuropsychology of Consciousness, ed. A. D. Milner
and M. D. Rugg. Academic Press, London, 1992,
pp. 263-278.
Schacter, D. L., McAndrews, M. P. and Moscovitch,
M., Access to consciousness: Dissociations between
implicit and explicit knowledge in neuropsychological syndromes. In Thought Without Language, ed. L. Weiskrantz. Oxford University Press,
Oxford, 1988, pp. 242-278.
Seidenberg, M. S. and McClelland, J. L. A distributed, developmental model of word recognition and
naming. Psychological Review 96, 523-568, 1989.
Shallice, T. and McGill, J., The origins of mixed
errors. In Attention and Performance VII, ed. J.
Requin. Erlbaum, Hillsdale, N J, 1978.
Shallice, T. and Saffran, E. M. Lexical processing in
the absence of explicit word identification. Cognitive
Neuropsychology 3, 429-458, 1986.
Sieroff, E., Pollatsek, A. and Posner, M. I. Recognition of visual letter strings following injury to the
posterior visual spatial attention system. Cognitive
Neuropsychology 5, 427-449, 1988.
Sieroff, E. and Posner, M. 1. Cueing spatial attention
during processing of words and letter strings in normals. Cognitive NeuropaTchology 5, 451-472, 1988.
E. Lfidavaset al./Lexical and semantic processing in neglect dyslexia
38. Umiltfi, C., and Moscovitch, M., Attention and PerJormance XV. MIT Press, Cambridge, MA, 1994.
39. Volpe, B. T., LeDoux, J. E. and Gazzaniga, M. S.
Information processing of visual stimuli in an 'extinguished' field. Nature 282, 722-724, 1979.
40. Warrington, E. K. Right neglect dyslexia: A single
case study. Cognitive Neuropsychology 8, 193 212,
1991.
41. Warrington, E. K. and Shallice, T. Semantic access
dyslexia. Brain 102, 43 63, 1979.
1085
42. Young, A. W., Conscious and nonconscious
recognition of familiar faces. In Attention and
PerJormance XV, ed. C. Umiltfi and M. Moscovitch. MIT Press, Cambridge, MA, 1994, pp. 153178.
43. Young, A. W. and De Haan, E. H. F., Face recognition and awareness after brain injury. In The
Neuropsychology of Consciousness. ed. A. D. Milner
and M. D. Rugg. Academic Press, London, 1992,
pp. 69 90.