Preserved semantic access in neglect dyslexia

\

Pergamon

PII] S9917Ð2821"85#99955Ð7

Neuropsycholo`ia\ Vol[ 24\ No[ 2\ pp[ 146Ð169\ 0886 Þ 0886 Elsevier Science Ltd[ All rights reserved Printed in Great Britain 9917Ð2821:86 ,06[99¦9[99

Preserved semantic access in neglect dyslexia  DAVAS\ TIM SHALLICE$ and M[ TERESA ZANELLA% ELISABETTA LA Dipartimento di Psicologia\ Universita di Bologna\ Viale Berti Pichat\ 4\ Bologna\ Italy ^ $SISSA\Trieste and Psychology Department\ University College\ London\ U[K[^ %Ospedale {Fraticini|\ Firenze\ Italy "Received 08 December 0884^ accepted 14 May 0885#

Abstract*The aim of this study was to investigate the preservation of semantic access in patients with severe neglect dyslexia for words and non!words[ Patients were given the following tasks] "0# reading aloud letter strings "_rst basic reading task#\ "1# making semantic decisions "categorial and inferential judgements#\ "2# making semantic decisions and reading the letter strings immediately afterwards "semantic!reading tasks#\ "3# reading letter strings again "_nal basic reading tasks# and "4# auditory control tasks[ Of 12 patients with visual neglect\ four showed neglect dyslexia for both words and non!words[ Of these four patients\ three showed a performance in the semantic tasks that was as good as in the auditory condition[ Moreover\ the reading of the patients improved dramatically in the semantic!reading tasks but this was not maintained in the _nal basic reading task[ Non!words showed only a minor improvement[ Findings are discussed in terms of an interaction between the attentional system and the di}erent reading routes\ and provide evidence that semantic routes are less a}ected by neglect[ Þ 0886 Elsevier Science Ltd[ All rights reserved[ Key Words] neglect dyslexia^ visual attention^ reading routes^ semantic access[

non!words than for words ð0\ 1Ł[ This e}ect "the lexical e}ect# suggests that lexical representation may be par! tially accessed[ Recently\ these phenomena "length and lexical e}ects# have been explained by Mozer and Behrmann ð10Ł as a result of interactions between lower and higher level processes in the context of a computational model of neglect dyslexia[ The lesion is held to result in an atten! tional de_cit that a}ects lower levels of processing*the output of one component of this model\ that is the so! called {BLIRNET|^ this produces left!sided degradation of this level of representation of the stimulus[ If the atten! tional de_cit is not too severe so that the left!sided infor! mation is registered to a certain extent\ the processed information may be still su.cient to activate higher order lexical:semantic representations in the so!called {Pull out Network|[ In other words\ if the degraded information _ts the preexisting representation of a word\ a correct reading response can result[ If an error is produced\ it tends to be of the same length as the stimulus[ This type of reasoning\ in which a stored representation is held to assist the recovery of degraded perceptual input\ cannot be applied to non!words\ as they are not represented in the lexical system[ Therefore\ according to these authors\ the better reporting of words compared with non!words\ can be seen as a result of interactions between lower and higher level processes[ A recent study by Ladavas et al[ ð06Ł con_rmed the

Introduction Unilateral neglect is a disorder in which patients do not report\ respond to or orient to stimuli presented con! tralaterally to the lesioned hemisphere "see\ for example\ papers in ð14Ł#[ One manifestation of this lack of respon! siveness to contralesional stimuli can be the failure to read verbal material that appears in the space opposite the damaged hemisphere[ This phenomenon is termed {neglect dyslexia|[ Patients with neglect dyslexia usually make errors in reading the left part of the written word and non!word "i[e[ the beginning in Western scripts#[ They can omit some of the letters or insert letters that are not present[ Alternatively\ they substitute some or all of the letters on the left side[ Interestingly\ in many neglect patients\ the number of erroneously substituted letters tends to match the number of letters actually present in the letter string ð7\ 17Ł[ This _nding "length e}ect# suggests that some information is available about the letters present on the left side[ One possibility is that there is an impaired rep! resentation of lexical information on the left which\ how! ever\ conveys information about word length[ In neglect dyslexia\ errors tend to be more frequent for Address for correspondence] Dipartimento di Psicologia\ Universita di Bologna\ Viale Berti Pichat\ 4\ Bologna\ Italy^ fax] 28!40!132975[

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assumption of the relative preservation of lexical access in neglect dyslexia patients[ In this study\ the authors found that\ relative to controls\ neglect patients per! formed very poorly in reading tasks aloud\ whereas they performed nearly normally in lexical decision "word vs non!word# and semantic decision "living vs non!living# tasks[ The proposal o}ered by the authors is a version of the quality of representation account that _ts with the Mozer and Behrmann position and more generally with that put forward\ among others\ by Farah ð8Ł to explain certain dissociations in patients with neglect and extinc! tion[ Neglect and extinction are assumed to result in poor!quality perceptual representations\ which supply degraded input to higher!level linguistic processing[ The poor!quality perceptual representations are held to be su.cient to subserve binary choices "e[g[ sameÐdi}erent matching of letters or objects#\ but not multiple!choice naming[ This sort of position can be developed in two rather di}erent ways[ Ladavas et al[ ð06Ł suggested developing it using the multiple route models standard in accounts of reading[ They pointed out that the non!lexical phono! logical route requires conversion from graphemic to phonological codes "i[e[ the compiled or assembled pho! nology#\ which\ in turn\ must be based on early and e.cient identi_cation of the component letters or letter clusters[ In other words\ the non!lexical phonological route depends heavily on multiple!choice identi_cation processes[ By contrast\ the semantic route may depend on a less detailed word!form representation\ in which component letters or letter clusters are not all processed individually[ This would mean that the non!lexical phonological route would have much more di.culty than the semantic route in dealing with a degraded letter string[ The same type of reasoning was used to explain the lexical superiority e}ect\ as the lexical routes are useless for non! words[ This interpretation\ of course\ does not explain why the patients did not use the lexical route for the reading task[ However\ to employ a list of mixed words and non!words\ as in the study by Ladavas et al[\ could have induced a bias towards the use of the non!lexical phonological route[ The alternative possibility is that the living:non!living discrimination can be carried out with a weaker or noisier output of the orthographic system than that required for reading aloud[ The degraded output of the orthographic system may be su.cient to support the correct category discrimination without being su.cient for the identi! _cation of the speci_c item itself[ This would follow from Farah|s account and is essentially analogous to the expla! nation given for related phenomena in semantic access dyslexia by Hinton and Shallice ð03Ł[ The performance of patients studied by Ladavas et al[ is indeed similar to that of certain semantic access and pure alexic patients who can carry out lexical decisions and perform category judgements on words that they cannot read aloud or identify at well above chance levels ð4\ 16\ 18Ł[ Di}erent types of prediction follow from the two possi!

bilities[ The _rst possibility is that the need to make a lexical or semantic decision biases the patient to make more use of the lexical phonological and semantic route"s# instead of the non!lexical phonological route[ This will explain why performance on a semantic decision was better[ Now\ Monsell et al[ ð08Ł have shown that combining the reading of words and pronounceable non! words alters processing by comparison with the situation in which the two types of stimuli are read in distinct sets^ they argue that subjects adjust their readiness to base the naming of the word on assembled! as opposed to whole! word!reading[ Thus\ mixing non!word! with word!read! ing would be expected to increase the reliance of subjects on the non!lexical route by comparison with the lexical route"s# that should predominate in word!reading[ If similar strategic processes are present in neglect patients then reading lists of words mixed with non!words will lead to a greater degree of neglect for the words than when the lists are composed only of words[ We therefore contrasted the reading of a mixed list of words and non! words with a pure list of words and a pure list of non! words[ If\ however\ the performance of neglect patients is more appropriately viewed within the broad framework pro! posed by Farah\ and in particular shows analogous characteristics to that of semantic access patients\ then di}erent predictions can be made[ The easiest semantic decisions for semantic access patients are judgements about which of two broad superordinate categories a word is in ð18Ł[ Instead\ when the decision between alter! natives requires the patient to identify the target word\ because the semantic connection requires an inference "inferential judgement#\ then performance would be expected to be especially poor[ Even if it were assumed that the inference is not performed consciously but by some process involving feature overlap\ this decision should be much more di.cult as it would be based on a much smaller set of features than the large number of features that could be used to di}erentiate between broad semantic categories[ The common features in the infer! ential decision could concern form "e[g[ penguin] tuxedo vs tracksuit#\ motion "e[g[ kangaroo] spring vs hanger#\ texture "e[g[ apricot] velvet vs hemp#\ material "window] glass vs wool#\ environmental sound "locomotive] rumble vs hoot#\ Italian cultural associations "stork] gynae! cologist vs psychiatrist^ cabbage] child vs old man# or potential context "peppers] lunch vs breakfast^ lentil] Christmas vs summer holiday#[ Then\ an intermediate result would be expected in a third type of judgement "categorical judgement#\ which used more narrow categories than the broad super! ordinate judgements and yet has been found to be easier than decisions based on speci_c features in a semantic access dyslexic patient "Warrington and Shallice\ 0868# ð18Ł[ This type of task could be solved using category membership because\ although both alternatives belong to the same broad superordinate category\ only one belonged to the same speci_c category as the target[

E[ Ladavas et al[:Preserved semantic access in neglect dyslexia

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words[ Patients who made more than 19) of errors of neglect dyslexia type on both words and non!words were then studied[ For this reason\ only four neglect dyslexia patients "T[L[\ M[G[\ B[G[ and B[M[# were selected from the population of 12 patients with severe left neglect[ The characteristics of the subjects inves! tigated are outlined in Table 0[ The initial experiment was carried out on the _rst of these patients who became available[

We therefore contrasted three types of semantic decision] one in which the choice was between two broad superordinate semantic classes "living:non!living judge! ment#\ one in which one of the alternatives was a word belonging to the same category as the target word "e[g[ mosquito] ~ea or cypress# "cate`orical jud`ement#\ and one in which an inference was required to select between alternatives "inferential jud`ement#[ In this latter case\ both terms of the pair belong to the same semantic cat! egory di}erent from that of the stimulus "e[g[ mosquito] car or aeroplane#[ On this type of theorizing\ performance should become much worse as one moves through the three alternative conditions[

Subject T[L[\ a right!hand retired woman\ su}ered a stroke at the age of 62\ 2 months before the testing was carried out[ She had a left hemiplegia but no visual _eld problems as tested through campimetry[ She had no language problems and was highly co! operative[ A CT scan showed a large hypodense area which occupied two!thirds of the lateral right hemisphere[ Her severe neglect is evident from the results shown in Table 0[

Method Patients with unilateral lesions a}ecting the right hemisphere drawn from the in!patient population of Fraticini Hospital were selected for the presence of horizontal visual neglect as assessed by a number of tests[ Visual extinction was not tested[ For the present purposes\ the relevant tests were] "0# to cross out {H|s| in a structured array of letters ð6Ł^ and "1# to cross out bells in a display of drawings of several objects ð00Ł#[ Patients who omitted more than 59) of the stimuli on the left in both tests were considered to show neglect\ and they were then tested for neglect dyslexia[ Few patients with visual neglect showed reading errors for words\ whereas most of them manifest the de_cit for non!words "see Table 0#[ Because the aim of the present study is to explore the degree of preservation of lexical and semantic access in neglect patients\ the investigation was con_ned only to patients who showed neglect dyslexia for

Stimuli and procedure The same set of words was selected to be used in a number of di}erent conditions and so was subject to a variety of con! straints[ Half of the stimuli were Italian words "44 stimuli# of at least three syllables\ and the other half "44 stimuli# were legal non!words obtained by substituting two letters[ For the non! words\ the substituted letters were located equally often on the left and on the right side of the stimulus[ All the words were concrete and denoted either living or non!living items[ Com! pound words were not used[ The length of the stimuli was six letters "09 stimuli#\ seven letters "05 stimuli#\ eight letters "23 stimuli#\ nine letters "11 stimuli#\ 09 letters "07 stimuli#\ or 00 letters "09 stimuli#[ The stimuli\ printed in upper case Palatino

Table 0[ Characteristics of patients with neglect dyslexia for non!words "P0ÐP08# and for words and non!words "T[L[\ M[G[\ B[G[\ B[M[#

Case

Sex\ age

P0 P1 P2 P3 P4 P5 P6 P7 P8 P09 P00 P01 P02 P03 P04 P05 P06 P07 P08 T[L[ M[G[ B[G[ B[M[

M\ 59 F\ 52 M\ 67 M\ 62 M\ 65 M\ 56 M\ 51 M\ 54 F\ 61 M\ 64 M\ 61 F\ 79 F\ 57 M\ 62 M\ 64 F\ 79 M\ 52 F\ 67 M\ 57 F\ 62 F\ 79 F\ 63 F\ 69

Onset of illness "months# 1 01 4 1 05 3 01 1 1 2 3 2 4 1 2 09 2 6 1 2 0 4 4

Cancellation tests Letters Locus of lesion L R RTPD RD RF RFD RD RPD RPD RFTPD RPD RD RPD RD RTP RTPD RPD RD RPD RPD RPT RFRP RFTP RFTP RPT

36 01 3 00 9 9 21 9 10 00 9 9 27 0 01 13 9 21 9 9 9 9 9

40 36 11 38 06 00 34 08 38 06 09 12 49 03 34 20 08 34 00 04 09 7 02

Reading task Bells L

R

Words

Non!words

9 9 4 7 03 9 2 0 01 4 9 9 4 9 4 8 0 2 9 9 9 9 9

5 6 05 06 06 5 06 03 06 05 6 2 06 6 03 01 03 06 5 7 1 3 5

82) 84) 71) 85) 87) 099) 84) 80) 87) 79) 099) 099) 099) 76) 76) 84) 80) 84) 099) 04) 11) 02) 05)

76) 62) 31) 64) 82) 71) 78) 48) 60) 65) 64) 27) 56) 62) 60) 42) 47) 78) 71) 9) 3) 9) 13)

Rright hemisphere^ Ddiencephalon^ Ffrontal lobe^ Pparietal lobe^ Ttemporal lobe[

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E[ Ladavas et al[:Preserved semantic access in neglect dyslexia

style "07 pt#\ were located on the centre of the page "A3 format#\ and presented horizontally[ They were printed on a sheet of paper and were presented one at the time by means of a movable window[ T[L[ was presented with a series of task\ namely baseline tests for neglect\ a basic reading task\ the semantic tasks\ a _nal basic reading tasks and auditory control tasks for the semantic tasks[ Each type of task was presented in a separate session and all the conditions were carried out in a week[ In the reading task\ each letter string was presented twice\ once in a list composed of both words and non!words "mixed condition#\ and once in a list composed only of words "words condition# or one composed only of non!words "non!words condition#[ The patient was instructed to read aloud the letter string[ In both the word and the non!word!reading conditions\ the patient was told about the lexical status of the letter strings[ In the mixed condition\ she was explicitly told that 49) of the letter strings were words and 49) were non!words[ In the semantic tasks\ the same list of words used for the reading task "words condition# was presented three times] once for the living:non!living judgement\ once for the semantic cat! egorial judgement "categorial judgement condition# and once for the semantic inferential judgement "inferential judgement condition#[ As in the reading conditions\ the stimuli were pre! sented one at a time by means of a movable window[ In the second and third conditions\ two words were spoken to the patient after the presentation of the written word[ In the cat! egorial judgement condition\ the pair was constructed in such a way that only one belonged to the same semantic category as the stimulus "e[g[ camel] elephantÐ_r!tree^ stork] swallowÐ asparagus#[ In the inferential judgement condition\ however\ both of the pair belonged to the same semantic category\ which was di}erent from that of the stimulus\ but only one member of the pair was related to the target by means of a common feature\ which could concern form\ motion\ texture\ cultural associations\ potential context\ etc[ The patient was instructed to make a decision about which of the two terms was more related to the target[ In order to test the possibility that errors arise from high! level cognitive di.culties rather than visual access di.culties\ in an additional test\ the stimuli were presented in the auditory modality as well as the force!choice items[ In this condition\ the patient was asked to perform both categorial and inferential judgements[

Results In the statistical analyses to be reported below\ the dependent variable was accuracy\ as indicated by error rate[ In the case of the reading task\ omitting or mis! reading one or more letter was considered to be an error for the whole letter string[ The scores reported below "see also Table 1# always refer to correct responses[

Word!reading condition In the basic word!reading task\ the performance of the patient was very poor in both the pure "3)# and mixed "3)# list conditions[ In contrast\ in the semantic tasks\ the performance was signi_cantly better in all three cases] for the living:non!living judgement "64)# and for both the categorial "67)# and the inferential "67)# judge! ments[ Moreover\ the errors do not seem to be related to visual access di.culties because\ in the control auditory semantic judgements\ the corresponding values were almost the same "67) and 71)\ respectively#[ On the other hand\ the better performance on the semantic tasks cannot be explained by assuming a general learning e}ect for the material operating over the course of the experi! ment because the performance on the _nal basic reading tasks in both the pure "6)# and mixed "3)# conditions was not signi_cantly di}erent from that found in the _rst basic reading conditions[

Non!word!reading condition As one would expect in the basic non!word!reading task\ the performance of the patient was very bad in both the pure "1)# and the mixed "9)# list conditions and did not show any improvement in the _nal reading task in either the pure "9)# or the mixed "9)# conditions[ The word! and non!word!reading errors were always of the so!called {Missing!Left| variety in which letters are omitted predominantly from the left part of the letter string "word] pomodoro:doro\ lenticchia:chia\ prezze! molo:molo\ elicottero:tero^ non!word] pimoduro: duro\ lantacchie:chie\ prizzemilo:milo\ alicotturo:turo#[ These consisted nearly always of the omission of all the letters up to a {neglect point| ð7Ł\ but occasionally\ a letter from the left would be intact "e[g[ cipollaÐcolla#[ The distribution of errors for each letter string for both the word! and non!word conditions in the _rst reading task is given in Fig[ 0[

Discussion The results of the present study are very clear and surprising[ Neither set of predictions is corroborated[

Table 1[ Performance of T[L[ on the tests used in Experiment 0 as a function of the lexical status of the letter string "words and non! words#\ semantic tasks "categorial and inferential judgement# and type of list "pure and mixed# First reading task Words Non!words P M P M T[L[ 3)

3)

1)

9)

Semantic task Cat[ J Infer[ J[ 67)

67)

Last reading task Words Non!words P M P M 6)

Each task was carried out in di}erent sessions in the order indicated[

3)

9)

9)

Auditory semantic task Cat[ J Infer[ J 67)

71)

E[ Ladavas et al[:Preserved semantic access in neglect dyslexia

150

Fig[ 0[ Percentage of letters correct and in the correct position "with respect to the right end of the string# for both word and non! word conditions in the _rst reading task as a function of a length of the letter string[

Consider _rst reading aloud] performance on the mixed wordÐnon!words list is virtually identical to that of the pure list[ There is no advantage as predicted of having a pure list[ Indeed\ errors on the pure word list condition are always of the missed!left variety and are typically non!words[ From the perspective of the classical three! route model of reading ð19Ł\ as non!words are the typical response\ the patient must clearly have used the non! lexical phonological route[ However\ there is no evidence that the use of a pure list was su.cient to shift the strategy used by T[L[ away from the use of the non!lexical phono! logical route[ The failure of the second prediction is more dramatic[ Despite showing severe neglect in both basic reading aloud sessions\ even with pure word lists\ T[L[ performed reasonably well and far above chance not only in the living:non!living semantic decisions "64) correct#\ cor! roborating the _nding of Ladavas et al[ ð06Ł\ but also on the categorial and inferential decisions "67) and 67) correct#[ Indeed\ she performed virtually at the same level with visual presentation on both these last two conditions as in the control auditory conditions "67) and 71) correct#[ Thus\ the errors made on this task can be pre! sumed to arise from high level cognitive di.culties rather than from the type of visual access di.culties that one would expect with neglect[ Most critically of all\ there was no tendency towards the presence of a poorer level of performance in the inferential condition where it had been presupposed that identi_cation of the stimuli was required in order to carry out the task[

If identi_cation of the words is indeed required in the inferential judgement task then this implies that the read! ing behaviour of T[L[ is not analogous to that of the semantic access dyslexia patients\ who are only capable of broad superordinate categorical decisions[ Moreover\ the position advocated by Farah\ that\ in neglect\ the poor quality of the perceptual representation can sub! serve a broad binary choice such as is required in the living:non!living judgement but not selection between multiple alternatives as required by identi_cation\ would not be a relevant framework for interpreting the results[ One possibility that needs to be considered is that the assumption made about the relative speci_city of item identi_cation required in the inferential judgements by comparison with other tasks was wrong[ If this assump! tion about identi_cation being necessary for good per! formance on the task is correct\ then explicit identi_cation of nearly all stimuli would be necessary to support T[L[|s level of performance on the task[ Thus\ far better naming of the stimuli should have been possible than the level of naming that occurred in the pure list condition\ which remained so poor[ In other words\ the patient with severe neglect dyslexia should be able to read; This strikingly counterintuitive prediction was tested in the next experiment[ The second experiment aimed to investigate the ability of patients with severe neglect dyslexia to identify a word once they had made a semantic decision about them[ Two new reading!aloud conditions were added to the previous procedure[

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E[ Ladavas et al[:Preserved semantic access in neglect dyslexia

Experiment 1 The stimuli and procedure were the same as in the previous experiment with the addition of two new reading conditions[ In these conditions\ the patient was asked to read the words together with non!words "mixed con! dition# after carrying out the categorial judgement "cat! egorial!reading condition# and after carrying out the inferential judgement "inferential!reading condition#[ In each of these conditions\ the patient was presented with a letter string "word or non!word# and then asked to make the judgement and immediately afterwards to read the letter string[ In the case of non!words\ the forced! choice items for the categorical and inferential judge! ments were the same as those for the words from which it was derived[ This was done because the non!word was obtained from a word by substituting two letters[ One possibility is that the semantic tasks nearly led to the subjects scanning further to the left[ To test this possi! bility\ the categorial and inferential judgements were also performed for non!words[ If better scanning was the cause of the better performance\ the same improvement should occur for non!words[ The overall structure of the experiment was that the patient was presented with baseline tests for neglect\ basic reading tasks\ semantic tasks "categorial and inferential judgement conditions#\ semantic!reading tasks\ _nal basic reading tasks and the auditory control tests for the semantic tasks[ The patients performed the categorial and inferential tasks twice\ once by itself and once when it was followed by reading it[ The living:non!living judge! ment was not given to the new patients in order to reduce the possibility of a general learning e}ect for the material[ Each type of task was presented in a di}erent session[ Three patients participated in this study\ and the charac! teristics of each of them are outlined in Table 0 "see M[G[\ B[G[ and B[M[#[ As already pointed out\ the subject in the previous experiment\ T[L[\ performed much better on the semantic decisions than in the basic reading task[ An obvious possi! bility is that the letters reported in the reading task\ although incomplete\ provided enough information to allow a good guess about the semantic category of the letter string[ That is to say\ the patients might have been using a guessing strategy based on the outcome of what! ever they were able to read[ Indeed\ it has been suggested by Patterson "personal communication# that\ in certain forms of letter!by!letter reading\ above!chance semantic categorization could be based on the explicit reading of a few of the letters of the word together with knowledge of the categories speci_ed in the judgement ð16Ł[ If\ however\ a process such as this were being used\ then a normal control subject too should be able to make correct semantic guesses when presented with the responses of the patients in the reading task[ To control for this possi! bility\ the letter strings corresponding to the utterances produced by each patient for words and non!words in the reading task were separately presented in a written

form to controls\ three di}erent controls being used for each patient[ The nine controls were matched to the three 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 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[ They were then asked to guess which of the two auditory presented items went best with the written letter string[ If the guess was correct\ then they were asked to guess the word:non!word from which it was derived[

Results The results of each patient will be presented separately and considered as three single cases[ The scores to be reported below always refer to correct responses\ and word and non!word!reading errors were always char! acterized by omissions of left!sided orthographic infor! mation[ For the statistical analyses\ comparisons of performances between di}erent conditions used McNe! mar Test\ and comparisons with chance used the Binomial Test[

Patient B[G[ Word conditions In the basic word!reading task\ the performance of the patient in the mixed and pure list conditions did not di}er signi_cantly in either the initial "02) vs 05)# or the _nal word!reading condition "3) vs 05)#[ B[G[|s performance on the semantic tasks was superior to that obtained in the reading tasks and better than chance in both categorial "66)\ P³9[9990# and infer! ential "66)\ P³9[9990# judgements when the items that were correctly read in the _nal reading conditions were excluded[ The presence of preserved semantic access in B[G[ was con_rmed by the results found in the categorial and inferential tasks performed immediately before the reading tasks "80) and 78)\ respectively#[ Moreover\ these values are virtually identical to those obtained in the control auditory semantic tasks "78) vs 80)#\ and strongly support the notion that semantic access is pre! served in this patient[ The new _nding is that having semantic access to visu! ally presented information improved B[G[|s reading ability in both the categorial and the inferential reading conditions[ When the reading performance in the sem! antic!reading and _nal reading tasks was compared\ a signi_cant improvement was found in the inferential reading condition "73) vs 3)\ respectively\ P³9[9990# and in the categorial reading condition "73) vs 3)\ P³9[9990#[ When the scores obtained in the _rst and last

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Table 2[ Performance of the three patients studied in Experiment 1 with words as a function of semantic tasks "categorial and inferential judgement# and type of list "pure and mixed# First reading task P M

Semantic task C[J[ I[J[

C[J[

Semantic¦reading tasks I[J[ C[J[ I[J[

Last reading task Auditory control task P M C[J[ I[J[

B[G[ 05) 02) 66) 66) 80) 78) 73) 73) 05) 3) 78) 80) M[G[ 04) 11) 63) 73) 76) 74) 71) 65) 31) 20) 62) 78) B[M[ 07) 54) 60) 60) 82) 82) 53) 71) 53) 45) 85) 82) –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– —

Fig[ 1[ Percentage of letters correct and in the correct position "with respect to the right end of the string# for both word and non! word conditions in the _rst reading task as a function of a length of the letter string[

reading condition were compared\ no signi_cant di}er! ence was found either in the pure list condition "05) vs 05)# or in the mixed condition "02) vs 3)#[ Thus\ there was no general learning e}ect in this patient "see Table 2#[

Non!word conditions In the _rst reading condition\ the performance in the pure and mixed conditions did not di}er signi_cantly "9) vs 6)#[ A similar pattern of results was found in the _nal reading condition\ where the scores in the pure and in the mixed list were virtually the same "4) vs 4)#[ The performance in the categorial judgement was signi_cantly better than chance "54)\ P³9[94# and at chance level in the inferential judgement "43)#[ When the score on the _nal reading condition "4)# was compared with the read! ing score in the categorial "05)# and inferential "16)# conditions\ there was found to be a signi_cant improve! ment in both conditions "P³9[94\ P³9[990\ one tail\

respectively#\ see Table 3[ However\ this improvement was less for non!words than for words both after cat! egorial "P³9[9990# and inferential "P³9[9990# reading semantic tasks[ As had occurred with T[L[\ reading errors were always of the so!called missing!left variety in which letters are omitted predominantly from the left part of the letter string "word] canguro:uro\ elicottero:zero\ ambu! lanza:anza\ peperone:brone^ non!word] manguto:guto\ alicotturo:turo\ arbulanta:anta\ piperona:rona#[ The distribution of errors for each letter string for both the words and non!words conditions in the _rst reading task is given in Fig[ 1[

Control for guessing The letter strings produced by the patient in the word categorial and inferential reading tasks were assigned by controls to the correct category at only chance rates "36) and 41)\ respectively#[ When controls were correct in

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E[ Ladavas et al[:Preserved semantic access in neglect dyslexia

Table 3[ Performance of the three patients studied in experiment 1 with nonwords as a function of semantic tasks "categorial and inferential judgement# and type of list "pure and mixed# First reading task P M B[G[ 9) M[G[ 1) B[M[ 14)

6) 3) 27)

Semantic¦reading tasks C[J[ I[J[ C[J[ I[J[

Last reading task P M

54) 43) 05) 16) 4) 4) 44) 44) 14) 16) 19) 6) 59) 59) 22) 33) 16) 04)

this task\ they were asked to guess the speci_c item and they had a low level of accuracy "10) and 07)\ respec! tively#[ The corresponding values for non!words in the categorial and inferential reading tasks are 37) and 40)\ and again\ as one would expect\ no one single item was correctly identi_ed by the controls[

Patient M[G[ Word conditions In the basic word!reading task\ the performance of the patient in the mixed and pure list conditions did not di}er signi_cantly "11) vs 04)#\ and this was also the case for the _nal word!reading condition "20) vs 31)#[ The performance on the semantic tasks is superior to that obtained in the basic reading tasks[ More critically it is much better than chance in both the categorial "63)\

P³9[9990# and the inferential "73)\ P³9[9990# judge! ments when the items which were correctly read in the _nal reading conditions were excluded[ This pattern of results is also found on the categorial and inferential tasks performed immediately before the semantic reading tasks "76) and 73)\ respectively#[ Moreover\ these values were very similar to those obtained in the control audi! tory semantic tasks "62) vs 78)#\ showing in this way that semantic access in this patient is preserved[ The new _nding is that having semantic access to the visually presented information improved the patient|s reading ability in both the categorial and inferential read! ing conditions[ When the reading performance of the patient in the semantic!reading and _nal reading tasks was compared\ it was found to show a signi_cant improvement in both the inferential reading condition "65) vs 20)\ P³9[9990# and in the categorial reading condition "71) vs 20)\ P³9[990#[ When the scores obtained in the _rst and last reading condition were com! pared\ there was a signi_cant improvement for the pure list condition "04) vs 31)\ P³9[991\ one tail#\ but no di}erence was obtained for the mixed condition "11) vs 20)#[ Thus\ there was a minor general learning e}ect "see Table 2#[

Non!word conditions In the _rst reading condition\ the performance on the pure and mixed conditions did not di}er signi_cantly "1)

Fig[ 2[ Percentage of letters correct and in the correct position "with respect to the right end of the string# for both word and non! word conditions in the _rst reading task as a function of a length of the letter string[

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vs 3)#[ In contrast\ in the last _nal reading condition\ the performance was better in the pure than in the mixed list "19) vs 6)\ P³9[94\ one tail#[ Performance in both the categorial and inferential judgements was at chance level "44) and 44)#[ When the score on the _nal reading condition "6)# was compared to the reading score in the categorial "14)# and inferential "16)# conditions\ performance was found to be signi_cantly better fol! lowing both judgement conditions "P³9[90 and P³9[994 one tail#\ see Table 3[ However\ this improve! ment was much less for non!words than for words after both the categorial "P³9[994 one tail# and the inferential "P³9[90 one tail# semantic judgements[ As for the previous patient\ reading errors were always of the so!called missing!left variety in which letters are omitted predominantly from the left part of the letter string "word] canguro:uro\ elicottero:sotero\ ambulanza:olanza\ peperone:lerone\ lenticchia:_schia^ non!word] manguto:uno\ alicotturo:otturo\ arbulanta: bulanta\ piperona:celona#[ The distribution of errors for each letter string for both words and non!words conditions in the _rst reading task is shown in Fig[ 2[

Control for guessing The letter strings produced by the patient in the word categorial and inferential reading tasks were assigned by control subjects to the correct category at only chance rates "41) and 42)#[ When controls were correct in this task\ they were asked to guess the speci_c item and correct identi_cation occurred rarely "15) and 19)\ respec! tively#[ The corresponding values for non!words in the categorial and inferential reading tasks are 49) and 40)\ and no single item was identi_ed correctly by controls[

Patient B[M[ Word conditions B[M[|s performance on the basic reading tasks was more complex than that of the previous patient[ In the basic word!reading task\ her performance was much bet! ter in the mixed than in the pure "54) vs 07)\ P³9[9990# list conditions[ However\ this di}erence did not occur in the _nal word condition "45) vs 53) n[s[# where the trend was in the opposite direction[ The large e}ect on the initial basic reading task between pure and mixed lists appeared to arise from a reduction in the degree of neglect during the _rst session[ In fact\ the mixed condition was run after the pure condition[ This partial recovery did not manifest itself in the other pat! ients "see Table 2#[ Also\ B[M[|s degree of neglect was unstable\ and this may explain the odd results on the

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clinical test for reading in which the performance on non! words was better than for words[ The performance on the semantic tasks was superior to that obtained in the reading tasks and was much better than chance in both the categorial "60)\ P³9[9990# and the inferential "60)\ P³9[9990# judgements[ In these analyses\ the items that were correctly read in the _nal reading conditions were excluded[ The normal\ or close to normal\ semantic access was also found in the cat! egorial and inferential judgements performed immedi! ately before the letter string reading task "82) and 82)\ respectively#\ i[e[ in the semantic reading task conditions[ Moreover\ these values were very similar to those obtained in the control auditory semantic tasks "85) vs 82)#\ indicating that semantic access in this patient is preserved[ Having semantic access to the visually presented infor! mation improved the patient|s reading ability\ although only in the inferential condition[ When the reading scores in the semantic!reading conditions and the _nal reading condition were compared\ the performance was sig! ni_cantly better only in the inferential!reading condition "71) vs 45)\ respectively\ P³9[991 one tail#[ The cor! responding value for the categorial!reading condition is 53) vs 45)[ When the scores that were obtained in the _rst basic and _nal reading conditions were compared\ a signi_cant improvement was found for the pure list condition "07) vs 53)\ P³9[9990# but there was no di}erence for the mixed condition "54) vs 45)#[ However\ the di}erence in the pure list condition appears to arise from the variability in the aforementioned degree of neglect[ Non!word conditions In the _rst reading condition\ the performance in the pure and mixed conditions did not di}er signi_cantly "14) vs 27)#[ B[M[|s performance on the categorial and inferential judgements was better than chance level "59) in both conditions#[ When the score on the _nal reading condition "04)# was compared to the reading score in the categorial "22)# and inferential "33)# conditions\ a signi_cant improvement in both conditions was found "see Table 3#[ As for the previous patients\ reading errors were always of the missing!left variety in which letters are omitted predominantly from the left part of the letter string "word] canguro:euro\ elicottero:cottero\ ambulanza: bulanza\ peperone:rone^ non!word] manguto:anguto\ alicotturo:licoturo\ arbulanta:bulanta\ piperona:rona#[ The distribution of errors for each letter string for both word! and non!word conditions in the _rst reading task is given in Fig[ 3[ Control for guessing The average guessing score of the three control subjects provides useful information about the strategy that the

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Fig[ 3[ Percentage of letters correct and in the correct position "with respect to the right end of the string# for both word and non! word conditions in the _rst reading task as a function of a length of the letter string[

patient may have used[ The letter strings produced by the patient were classi_ed by controls at a level that is superior to that expected by chance with word stimuli in both the categorial and inferential judgements "47) and 68) correct responses\ respectively#[ In other words\ when the controls were asked to guess which of the two auditory presented items went best with the written letter string\ their performance was better than chance[ More! over\ when the categorial and inferential judgements of controls were correct\ they were also able to identify the word at a good level of accuracy "41) and 58)\ respectively#[ The corresponding values for the per! formance of controls on non!words in the categorial and inferential reading tasks are 48) and 43)\ and they were unable to identify a single non!word when they judged correctly[

General discussion The most basic aspect of the present _ndings is that\ in the three patients studied in Experiment 1\ all of whom showed very severe neglect in reading\ the performance in two critical semantic tasks was far better than would be expected from their initial reading!aloud results[ Moreover\ as with patient T[L[ studied in Experiment 0\ their level of performance on the two semantic tasks was not much di}erent with visual presentation from that in the control procedure of using auditory input[ This con_rms the results of Experiment 0 in three new patients[ The key _nding of the present experiment was the way

that the patients were able to read words immediately following the semantic decisions "the induced reading task# at a far higher level than in the simple reading! aloud condition "the _rst and _nal basic reading tasks#[ In fact\ the _ndings were very clear in two of the patients\ M[G[ and B[G[\ and rather less so in the third\ B[M[ We will\ for the present\ restrict consideration to M[G[ and B[G[ and discuss B[M[ later[ In M[G[ and B[G[\ the _ndings clearly con_rm the prediction made following Experiment 0\ that patients with neglect dyslexia\ show! ing preservation of semantic judgements for words that they could not originally read\ should be able to read the word aloud following the semantic processing of the word[ It has been shown that neglect patients can over! come\ to some extent\ their de_cit by voluntarily orienting attention in the contralesional direction ð04Ł[ Therefore\ a possible explanation might be that the basic phenomenon results from a general improvement in the processing of lexical strings\ due to better scanning of the left[ That is not the case[ Performance of all patients on reading non! words following the semantic task remains very poor\ and little or no better than on the _rst basic reading task[ For all patients\ the improvement is very much greater with words[ Even so\ if the e}ect were the result of a general increase in scanning to the left\ non!words should be read at a very much better rate[ A second line of evidence\ that there is not a general improvement in attention to the left following the sem! antic task\ comes from a qualitative di}erence in the way that reading occurs with words and with non!words in that condition[ With non!words\ 52) of all B[G[|s

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responses were of the missing!left variety in which more letters are omitted in the left than in the right part of the word\ and the only correct letters in the response nearly always consist of a continuous subset of the rightmost letters of the string^ this compared with only 04) of such responses when the stimuli were words[ For M[G[\ such a missing!left type responses occur in 43) of trials with non!words\ and only 10) with words[ This means that\ for the majority of the non!words\ the attention of the patients was not drawn to the left[ Thus\ it is not a change in strategic attentional control resulting from performing the semantic task that is the major factor in the ameli! oration of the neglect\ although this may be a subsidiary factor[ In addition\ one can see that it is not simply a general e}ect of learning the material[ Testing of reading aloud of the same control list on the session following that in which the semantic tasks were carried out "_nal basic reading task# led to virtually identical performance to that on the original testing "_rst basic reading task#[ Per! formance on the _nal reading task was again signi_cantly worse than that on the semantic task for M[G[ and B[G[ Therefore\ it seems that the major factor in producing an amelioration of neglect is the actual use of the semantic route itself[ Before considering the attentional control of the di}erent reading routes\ it is necessary to discuss the reading of the third patient B[M[ The pattern shown by B[M[ was rather di}erent[ Her reading following the inferential semantic task was signi_cantly better than her _nal baseline reading\ but this was not the case in the categorial!semantic task[ Moreover\ analogous e}ects were shown when the stimuli were non!words\ and\ unlike the other two patients\ the e}ects were no greater with words[ Consideration of a third control procedure suggests an explanation for the di}erent pattern of results in B[M[ by comparison with the other patients[ B[M[|s neglect was much more mild and unstable than in the other two patients\ and this was evident not only in a higher per! centage of the letter strings being correctly read but also in a higher number of letters being correctly reported when a word was misread[ Of course\ if most of a word is read correctly\ then the possibility exists of the forced! choice semantic tasks being carried out at above!chance levels by guessing based on the detected letters "see ð12Ł for a discussion of such strategies in pure alexia#[ This was tested for each of the three patients by presenting three matched controls with the letters that the patient had produced in the initial baseline reading test[ The controls then had to guess the appropriate response in the two forced!choice semantic tests[ The results of the controls matched to M[G[ and B[G[ were essentially at chance on the guessing tasks[ However\ those matched to B[M[ were considerably above chance[ Therefore\ one cannot rule out the possibility that B[M[|s good per! formance on the semantic tasks is merely a product of guessing based on information about the letters that she

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explicitly perceived[ In pure alexia\ it is known that a strategy of guessing based on explicitly perceived letters leads to a di}erent pattern of performance on semantic tasks from a strategy of attempting to read the word as a whole ð5\ 16Ł[ It is plausible that it would do so in this situation too[ This means that it is most appropriate to con_ne theorizing about the preservation of reading after semantic processing to M[G[ and B[G[\ whose baseline performance was too low to allow for an e}ective intel! ligent guessing strategy to operate[ The con_rmation of the prediction about reading aloud being far superior after the semantic tasks than in the basic reading tasks means that the analogy between the performance of severe neglect patients on the sem! antic category task and that of semantic access dyslexic patients is not an appropriate one^ semantic access pat! ients do not show an improvement of this magnitude in naming following a semantic task ð4\ 16Ł[ In addition\ the good reading performance in the experimental tasks indicates that Farah|s position that the poor quality per! ceptual representation underlying neglect can subserve binary choices only is not relevant to this phenomenon as patients under the present circumstances explicitly identify the items\ and the identi_cation requires a selec! tion between multiple alternatives[ The major computational model of neglect dyslexia is that of Mozer and Behrmann ð10Ł[ From an initial consideration\ it might appear that this model in its cur! rent form would be able to explain the results[ Indeed\ the mechanism in the model\ by which lexical:semantic knowledge helps to compensate for degraded perceptual information "the output of BLIRNET#\ would produce explicit identi_cation of the word as well as merely sup! porting broad categorical decisions[ One could make a minor addition to that model by assuming that individual semantic units within the so!called {pull out network| could be partially activated from above[ When relevant words are presented\ the appropriate letter cluster units would then be activated from above as well as\ to some extent\ from below and so would tend to be su.ciently strongly stimulated to allow lexical access[ Clearly\ such a phenomenon would not occur for non!words[ However\ more detailed consideration shows that it is implausible that the model would give rise to e}ects of the magnitude observed in this study[ First\ consider the bottom!up processes in the model[ Our patients showed only a very weak lexical superiority e}ect in the basic reading tasks[ In these tasks\ word!reading was very poor[ The patients are not the type of mild neglect patients whose pattern of lexical superiority is well captured by MORSEL[ Instead\ they su}ered from very severe neglect[ To simulate their basic reading performance with MORSEL\ one would need to assume the presence of very severe de_cits of the attentional mechanism\ meaning that the output of BLIRNET would be very weak for letters on the left side of the words so that the units for the cor! responding letter clusters would receive little or no acti!

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vation from below[ Secondly\ turning to the top!down e}ects\ a semantic task like a living:non!living judgement or deciding whether a word has a stronger relation with word X or word Y in\ say\ the inferential task would surely leave a large number of words as potential can! didate responses from top!down activation alone[ Thus\ when the patient is faced with the choice between fan and hairdrier to go with helicopter\ the relation between fan and helicopter is neither one of a common category nor one of a simple categorial link[ Thus\ the top!down acti! vation of letter clusters must be\ at most\ weak[ Even so\ when pooling these two sources of activation\ the weak top!down activation has to combine with the grossly degraded input from BLIRNET to give the high levels of activation necessary for speci_c lexical access[ It is very di.cult to imagine how this type of top!down e}ect can be su.cient when the output of BLIRNET is so poor\ as in the case in which the patient read only the last one or two syllables of _ve syllable words[ Even so\ control subjects provided with the output of the patients\ pre! sumably related to the output of BLIRNET\ did not perform better than chance in the semantic decisions[ Moreover\ the e}ect must be to generalize all words since\ in these neglect patients\ the visual semantic judgements are as good as the auditory control judgements[ In the literature on neglect dyslexia\ little consideration has been given to the di}erent reading routes[ However\ in the basic reading task\ the responses of our patients are generally non!words\ indicating that a non!lexical phonological procedure has been used[ In the semantic tasks and also in the semantic reading task\ the semantic route is presumably being used[ This suggests\ therefore\ that di}erent routes are\ in fact\ primarily used in these two conditions[ Why might the use of di}erent routes interact with neglect< It seems plausible that the use of the semantic route requires\ but also leads to\ a broadening of the attentional focus\ while the use of non!lexical phono! logical correspondences involves a more narrow atten! tional focus[ As far as a broader attentional focus being involved when the semantic route is used\ this is com! patible with the way that latency for semantic category decisions is una}ected by word length even when multi! syllabic words are used ð01Ł\ unlike the corresponding e}ects for naming latency ð09\ 02Ł\ where phonological routes seem more likely to be relevant[ By contrast\ it seems plausible that the use of the non!lexical phono! logical route would be linked to a narrower attentional focus\ given that one assumes that the transmission of information about the relevant level of units*sub!syl! labic or syllabic*is at least partially serial and results in achieving the so!called {assembled| phonological rep! resentations[ To assume partially serial processing when using non! lexical spelling!to!sound procedures might seem to con! ~ict with certain views on the operation of the phono! logical route[ However\ it should be noted that\ even when experiments provide evidence for parallel activation

of output phonological features given written input ð2Ł\ the large majority of stimuli used are monosyllabic[ Moreover\ connectionist models\ that presuppose par! allel activation of phonological features from ortho! graphic representations\ have been tested with monosyllabic words ð15Ł\ and the extension of such mod! els to multisyllabic words may involve more than a mere scaling up of input and output representations ð13Ł[ By contrast\ the stimuli in the current experiments involve words of at least three syllables[ Another factor is that the orthographic representations of long words have considerable redundancy because words are a small subset of the relevant orthographically possible letter strings[ This is much less so for sub!syllabic or syllabic units^ more precise speci_cation of each gra! pheme and its spatial position is required[ In the latter case\ the existence of multiple perceptual units of the relevant level within the same display could well lead to a greater bias to the right by comparison with the single perceptual unit\ that is the input to the semantic route[ The existence of multiple perceptual units in a display has been shown to lead to severe neglect in many other perceptual tasks ð05\ 07Ł and\ more positively\ if there is an assembly process used when letter strings are being transmitted by the non!lexical phonological route\ it should be possible to _nd speci_c interference in the naming of those stimuli that require this route[ Indeed\ retaining a digit load has been shown to produce a speci_c interference for low!frequency regular "but not exception# words\ which are the words that would rely most on this route for naming ð3\ 11Ł[ The position that the di}erence in reading performance between the basic and the experimental tasks re~ects the use of di}erent reading procedures in the two situations gives rise to three additional questions[ First\ why should patients use the attentional mode appropriate for the non!lexical phonological procedure in the basic reading condition< Reading aloud of individual words normally relies on the use of the phonological route"s#[ Assume that there is some modulation of the operation of the route"s# when it receives non!lexical\ as opposed to lexi! cal\ input[ This has even been suggested for a model in which non!lexical and lexical processing are as integrated as in the Seidenberg and McClelland model ð08Ł[ Then\ one thing that the modulation is likely to a}ect is the control of the sequence of parts of the input string to be admitted in turn to the spelling!to!sound translation process*the control of the attentional window[ With such an approach\ the size of the attentional window admitting graphemic input to the spelling!to! sound translation process must depend on some rapid preprocessing[ For instance\ the degree of activation of higher level lexical units could be used[ If only weak activation is occurring at that level\ then an initially broad window\ suggested by migration errors\ would be rapidly narrowed[ Adapting the terminology of Mozer and Behrmann ð10Ł\ if the output of BLIRNET led to weak activation at lexical levels\ this non!lexical attentional

E[ Ladavas et al[:Preserved semantic access in neglect dyslexia

mode would be adopted[ What letters would be admitted to the spelling!to!sound translation process on the non! lexical attentional mode< Presumably these would be let! ters for which BLIRNET activation was strong\ namely ones not at the left end of the letter string[ Thus\ situations will occur in which letters at the left end of the string never enter the attentional window for the spelling!to! sound translation process\ and a missing!left error occurs[ This would correspond phenomenologically to the selec! tion of which procedure to adopt and of which letters to be sounded out being dependent on what letter infor! mation is available at the explicit level[ The second question is] Why\ if the semantic route has been used successfully in the experimental task\ does it not continue to be used in the _nal basic reading task< In the _nal basic reading task\ the patients performed as poorly as in the _rst basic reading task\ and they showed the same error pattern of missing the leftmost letters and typically produced non!words[ It would appear that any attentional mode selection that goes with the pre! dominant use of the semantic route is not under the explicit untrained control of the patient[ Thus\ it cannot be applied to subsequent tasks without being made explicit or being induced by an experimental task which activates a speci_c task schema[ Thirdly\ why do so few neglect patients present neglect dyslexia for words "3 out of 12 in our sample#< In our study\ this type of phenomenon is observed only when neglect dyslexia for non!words is very severe[ Across our neglect sample of 12 patients\ all but the four exper! imental patients scored 27) or better with non!words[ Their word!reading performance was 79) correct or better[ By contrast\ the experimental patients ranged from 9 to 13) correct on reading non!words and from 01 to 11) with words[ One possibility is that this di}er! ence in pattern could be explained by the attentional focus being more sharply restricted in the experimental subgroup of four patients[ With the argument presented above\ a fair degree of lexical activation would be expected to result from the initial exposure to words in the other patients given their non!word performance\ and so the proposed restriction of the attentional window for entry to the spelling!to!sound translation process to the right would tend not to occur with words[ In this study\ we have documented patients who\ despite severe neglect dyslexia\ can read words well fol! lowing semantic judgements made on words[ This occurs because the use of the non!lexical phonological route is more subject to the e}ect of neglect than the use of the direct semantic route[

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Acknowled`ements*Elisabetta Ladavas was supported by grants from the CNR and MURST and Tim Shallice by a grant from the Wellcome Foundation[

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