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R. Mycroft et al. Journal of NEL Neurolinguistics 149


R. Mycroft et al. / Journal of Neurolinguistics 15 (2002) 99±108 NEL 149

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Journal of Neurolinguistics 15 (2002) 99±108 www.elsevier.com/locate/jneuroling

Preserved access to abstract letter identities despite abolished letter naming in a case of pure alexia
R. Mycroft a, J.R. Hanley b,*, J. Kay a
b a Department of Psychology, University of Exeter, Exeter, UK Department of Psychology, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, UK

Abstract In this paper, we discuss the letter processing dif?culties of a patient (MS) with pure alexia after left hemisphere stroke who is unable to read any words aloud despite preserved writing and good performance at naming orally spelled words. MS is completely unable to name visually presented letters even though she can name them when they are presented in other modalities. Despite her poor naming, she can distinguish correctly oriented letters from mirror reversals and can perform accurate cross-case matching of visually presented letters. It, therefore, appears that MS is able to access the abstract identity of visually presented letters despite her total inability to name them. This is a more precise form of letter processing impairment than that which has been reported in previous cases of pure alexic patients who are unable to name visually presented letters [Caplan, L.R., & HedleyWhite, T. (1974). Cueing and memory function in alexia without agraphia: a case report. Brain, 115, 251±262; Miozzo, M., & Caramazza, A. (1998). Varieties of pure alexia: the case of failure to access graphemic representations. Cognitive Neuropsychology, 15, 203±238; Sevush, S., & Heilman, K.M. (1984). A case of literal alexia. Brain & Language, 22, 92±108]. It suggests that representations of the graphemic identities of letters used in reading are either modality speci?c or else they are hemisphere speci?c [Saffran, E.M., & Coslett, H.B. (1998). Implicit vs. letter-by-letter reading in pure alexia: a tale of two systems. Cognitive Neuropsychology, 15, 141±165]. Her letter processing impairment also appears to be different from that observed in a letter-by-letter reader [Perri, R., Bartolomeo, P., & Silveri, M.C. (1996). Letter dyslexia in a letter-by-letter reader. Brain & Language, 53, 390±407] who could name visually presented letters with reasonable degrees of accuracy despite a dif?culty in processing their abstract identity. q 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Alexia; Letter-by-letter-reading; Letter processing

* Corresponding author. Tel.: 144-1206-874331; fax: 144-1206-873598. E-mail address: rhanley@essex.ac.uk (J.R. Hanley). 0911-6044/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved. PII: S 0911-604 4(01)00003-3

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1. Introduction Many alexic patients employ a reading strategy known as letter-by-letter reading in which the time taken to read words aloud is extremely long, and increases linearly with the numbers of letters in a word (Arguin, Bub & Bowers, 1998; Behrmann, Plaut & Nelson, 1993; Chialant & Caramazza, 1998; Kay & Hanley, 1991; Patterson & Kay, 1982; Reuter-Lorenz & Brunn, 1990; Saffran & Coslett, 1998; Warrington & Shallice, 1980). The monotonic relationship between letter length and reading speed suggests that these patients process letters serially when they are reading words aloud. It is now widely believed that patients adopt this strategy as a consequence of a letter processing de?cit that makes it impossible for them to process in parallel the abstract identity of visually presented letters. Abstract identities are representations that specify the graphemic identity of a letter but are neither visual nor phonological, and are independent of font and case (Coltheart, 1981). Consistent with this account, virtually all letter-by-letter readers either make errors when attempting to name visually presented letters, or else they process single letters relatively slowly [see Behrmann et al. (1998) for a review]. In addition, the severity of the letter processing de?cit appears to be one of the main factors that is associated with individual differences in reading speed (Shallice, 1988) in letterby-letter reading. 1 There is, however, a smaller group of alexic patients who are unable to read any letters or words at all, despite the fact that their writing ability appears to be completely unimpaired. Dejerine (1892) provided one of the ?rst and most detailed accounts of the written and spoken language processing abilities of an alexic patient of this kind, and he also provided anatomical evidence concerning the nature of the brain lesions that might cause it. Dejerine's patient (Monsieur C) was unable to identify any written letters either in words or when he was shown them one at a time, even though he appeared to be able to describe their visual form accurately. Dejerine believed that Monsieur C's alexia was the consequence of a lesion that made it impossible for visual information from either hemisphere to access letter and word level representations stored in the angular gyrus in the left hemisphere (for further discussion of this case, see Bub, Arguin & Lecours, 1993; Hanley & Kay, 2001). Following Geschwind (1965a,b), it is commonly argued that reading impairments occur in patients of this kind because left hemisphere reading centres are cut off from visual information in the right visual ?eld by a right homonymous hemianopia. They are cut off from visual information in the left visual ?eld by a lesion of the corpus callosum that prevents transfer of visual information from the right to the left hemisphere. An important issue that has not yet been satisfactorily resolved (Bub et al., 1993) is the extent to which alexic patients such as Monsieur C are suffering from a similar form of reading disorder to that which is observed in letter-by-letter reading. One possibility is that it is the severity of their letter processing de?cit that prevents alexic patients such as Monsieur C from reading words letter-by-letter. Consistent with this, the two pure alexic patients reported by Coslett and Saffran (1989, 1992) who were unable to name any visually presented words were also totally unable to name letters. Binder and Mohr
1 The other major factor that in?uences reading speed is whether or not the patient suffers from an additional word level impairment (Hanley & Kay, 1996).

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(1992) observed that ?ve letter-by-letter readers were all able to name letters more accurately (range ? 96±100%) than ?ve alexic patients who were unable to read any words aloud (range ? 23±85%). Alternatively, one might argue that the nature of the letter processing impairment is qualitatively different in the two types of patient. It has been suggested by a number of theorists (Arguin & Bub, 1994; Coslett & Saffran, 1989; Reuter-Lorenz & Brunn, 1990) that letter-by-letter readers have dif?culty in establishing the abstract identity of visually presented letters. Although it may be the case that alexic patients who are unable to read any words aloud are simply more severely impaired at generating abstract identities of letters, it is also possible that the locus of their letter processing impairment may be slightly different. In this paper, we examine the letter processing abilities of a pure alexic patient who, like Monsieur C (Dejerine, 1892), is unable to read any words aloud. Is it the case that this patient is generally impaired at processing written letters, or can the locus of the de?cit from which she suffers be speci?ed quite precisely? If so, does her problem re?ect a word ?nding problem for the names of letters, or is she unable to establish the abstract identity of visually presented letters (cf. Miozzo & Caramazza, 1998)? Does the nature of her letter processing impairment differ from that observed in letter-by-letter reading; if so is it a more severe impairment or is it qualitatively different? If she has a problem in recalling the name of visually presented letters, how does she perform when asked to retrieve letter names in other tasks?

2. Case report MS is a female patient who became alexic following a left hemisphere CVA in 1994 when she was 80-years-old. The tests reported in this paper were carried out 4 years later, by which time she had suffered three further CVA's (the ?rst giving left leg weakness, the second giving right-sided weakness), none of which appeared to have had any additional effect on her language processing ability. Her spoken language comprehension was intact. Her speech was ?uent, but she did have some anomic word-?nding problems. She had a right hemianopia as a result of the original CVA. MS's principal impairment was that she was unable to read. She told us that she could not read any letters or words aloud whatsoever. Despite this, her writing was unimpaired. For example, she was able to write an easily legible and comprehensible paragraph of prose for us. When she was subsequently given a passage of her own writing to read, however, she could not begin to decipher it. A speech therapist had attempted to remediate her reading problems by a number of different strategies. These included attempts to learn a small set of high frequency words by sight, and attempts to learn to recognise groups of letters that co-occur frequently in English words. She had also been taught a strategy that encouraged her to recite the alphabet in an attempt to ?nd the name of the letter that she was looking at. Unfortunately, MS told us that none of these strategies had proved at all effective, even though she felt highly motivated to try to learn to read again.

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3. Visual processing of letters 3.1. Letter discrimination: mirror reversal (PALPA test no. 18, Kay, Lesser & Coltheart, 1992) MS was given a sheet of paper containing 18 correctly oriented letters (nine in uppercase and nine in lower-case) and 18 mirror reversed letters (nine in upper-case and nine in lower-case). She was asked to tick all of the real letters. Her score was 35/36 correct. Mean score for 25 control subjects on this test is 35.44/36. She performed this task unhesitatingly. 3.2. Cross-case matching of letters (PALPA test nos. 19 and 20) MS was required to select from two alternatives the upper-case form that matched a particular visually presented lower-case letter. The task was then repeated with MS being asked to select from two alternatives the lower-case form that matched a particular visually presented upper-case letter. MS was 26/26 correct on both tests and performed the tasks at a normal speed. 3.3. Visual Search for letters (RPAB test no. 15, Whiting, Lincoln, Bhavnani & Cockburn, 1985) MS was shown the letter `E' and was asked to search through six rows of letters crossing out all of the `E's that she could ?nd. The rows contained 52 letters of which she crossed out 42. This score was within the normal range for controls (49.99, sd ? 4.50). 4. Letter naming 4.1. Written letter naming MS was shown a series of written letters one at a time in a random order to name (PALPA Test no. 22). She was unable to name any of the letters correctly despite considering each letter carefully for several seconds. 4.2. Spoken letter-written letter matching (PALPA test no. 23) MS heard a letter name and was asked to point to the correct written letter from four alternatives. She was correct on only 16/26. The task was repeated, but with letter sounds rather than letter names being presented. MS was correct on only 14/26 trials. Eight letters were identi?ed correctly by MS on both occasions. These were a, b, d, g, o, q, s, v, and x. 4.3. Identifying letters from motor patterns In this experiment, MS's ?nger was guided across a table-top to trace out the shape of a letter. She was then asked to name the letter. This occurred with a total of nine letter shapes. MS named 8/9 correctly. The task was repeated but this time her eyes were closed.

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She named 7/9 letters correctly. The errors that MS made involved producing the name of a visually similar letter. For example `n' was named as `h'. Identifying the ?rst letter of auditorily presented words. A list of 10 three-letter words (e.g. pen) was read out to MS one at a time. MS was asked to name the ?rst letter of each word. She scored 10/10, responding quickly and con?dently. 4.4. Identifying letters from phonemes In this task, MS was given 13 letter sounds and was asked to supply the letter that was associated with that phoneme (e.g. for the letter `a' she heard /ae/ and had to respond `a'). She was correct on 13/13 trials. She also scored 13/13 when she heard the letter name and had to respond with the correct letter sound. 5. Lexical processing 5.1. Reading words aloud MS's ability to read words has been examined on a number of different testing sessions. She is completely unable to read words aloud, the responses that she makes bear little resemblance to the target item. For example, during one testing session, we gave her the word `hen' to read. She began by trying to identify the constituent letters one by one. However, she experienced great dif?culty in naming any of the letters. She referred to an alphabetic chart beside her and recited the alphabet to herself. All three letters were misidenti?ed, and she appeared unconvinced that any of the letter names she provided were correct. She then offered erroneous guesses `him' and `?g'. 5.2. Identifying words from orally presented letter names MS was asked to identify 24 words that were spelled aloud orally to her. The list contained an equal number of words comprising three, four and ?ve letters. Half of the words at each letter length were regular and half were irregular. She was correct on 7/8 three-letter words, 7/8 four-letter words and 7/8 ?ve-letter words. Her three errors were all on irregular words. 5.3. Lexical decision MS was presented with 48 printed words, each of which contained four letters. Twentyfour were real words (e.g. nest), 12 were legal pseudo-words (e.g. sten), and 12 were illegal non-words (e.g. tsne). She made 32/48 correct decisions. She was 9/24 correct on the real words, 11/12 correct on the legal pseudo-words, and 12/12 correct on the illegal non-words. She responded immediately to all of the illegal non-words, but took several seconds over all of the legal pseudo-words and real words. Overall her performance was signi?cantly better than chance (z ? 2.165, P ? 0.015). However, the ability to distinguish illegal non-words from real words is almost certainly possible without the need to access lexical representations. When the illegal non-words were removed from the analysis, then MS's performance was no longer better than chance (56% correct). Overall, MS appears to

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show a response bias to say `non-word'; she responded `word' on only 10/36 of the word and pseudo-word trials. In conclusion, therefore, MS's performance on this task does not demonstrate that she can reliably access lexical representations of visually presented words. However MS is able to distinguish illegal non-words from real words signi?cantly better than chance. The ability to discriminate between words and random letter-strings would not be possible if a patient was unable to determine the identity of visually presented letters. What MS's performance on this task does provide, therefore, is evidence that she can recognize the identity of visually presented letters when they are presented as part of a letter-string. 6. Discussion It is clear that MS is suffering from a form of pure alexia similar to that observed by Dejerine (1892) in a number of respects. She is unable to name any visually presented letters or words whatsoever, and is unable to use a letter-by-letter reading strategy. Although MS continues to be able to write, she cannot read what she has just written. The main purpose of this investigation was to attempt to locate the point at which her processing of visually presented letters breaks down. MS is able to search accurately through a set of visually presented letters for examples that resembled the standard that she had been given. This suggests that her ability to perceive the appropriate visual form of letters that she is looking at is normal. She is also able to distinguish correctly oriented letters from mirror rotations with the same level of accuracy as controls. Employing the terminology used recently by Miozzo and Caramazza (1998, p. 227), this pattern of performance suggests that MS can access ?a representation that encodes letters as speci?c visual objects with particular canonical orientations?. MS is also able to perform crosscase matching of visually presented letters without making any errors. In the terms of Miozzo and Caramazza (1998, p. 227), this ability suggests that MS can also access the next level of processing: ?a representation that speci?es abstract letter identities independent of their speci?c visual forms?. MS performance on the visual lexical decision task supports this conclusion and also shows that she can recognize the abstract identity of letters when they are presented simultaneously. How does this pattern of performance compare with the letter processing skills of other pure alexic patients who are unable to read words letter-by-letter? Dejerine (1892) reported that Monsieur C could see letters perfectly (?Z looked like a serpent, P looked like a buckle, and A resembled an easel?), but did not recognise them as familiar visual forms. Nevertheless, Dejerine did not administer any tests to Monsieur C that would indicate the precise level of breakdown in his letter processing skills (Bub et al., 1993; Hanley & Kay, 2001). The pure alexic patient described by Sevush and Heilman (1984) had a slightly less severe letter-naming de?cit (21/77 letters named) than MS but was impaired at cross-case matching. Caplan and Hedley-White's (1974) pure alexic could correctly realign letter tiles that had been rotated away from their normal orientation. This suggests that the patient was able to access preserved representations of letters as speci?c visual objects, and seems comparable to MS's ability to distinguish real letters from mirror

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reversals. However, this patient was not administered any cross-case matching tasks, so it is not possible to determine whether or not he could access abstract letter identities. Most interesting of all, Miozzo and Caramazza (1998) report a pure alexic patient with no ability to name visually presented letters (GV) who was able to distinguish real letters from pseudo-letters and could identify canonical letter orientations. Crucially, however, this patient was extremely inaccurate at deciding whether or not two physically different letters had the same name. MS's good performance on cross-case matching therefore provides an interesting dissociation with GV. Although both patients can recognise letters as familiar visual forms, it appears that MS, unlike GV, can access abstract identities of visually presented letters. MS is unable to name (or even recognise the name of) visually presented letters yet she is good at cross-case matching. On the assumption that the abstract identity of a letter mediates between the representation of its visual form and the representation of its name in the speech production system, then this ?nding suggests that MS is suffering from a disconnection between preserved abstract identity representations of letters and the representation of their names in the output lexicon. It is important to point out that this naming problem is not simply an anomia for letter names because MS can retrieve letter names in a variety of tasks that do not involve visual presentation. These include naming the ?rst letter of spoken words, naming letters from tracing their shape with a ?nger, and naming letters from hearing the letter sound with which they are typically associated. The ?nding that MS's letter naming de?cit is speci?c to the naming of visually presented letters is somewhat counter-intuitive as it suggests that different abstract identity representations might be accessed following visual presentation from those that are accessed following presentation in other modalities. If the same representations of abstract letter identity were used for all modalities, then MS should have performed no better at naming letters following auditory or haptic presentation than she does following visual presentation. Is there any alternative explanation of this pattern of performance that does not involve postulating the existence of separate abstract identity representations for letters presented in different modalities? Saffran and Coslett (1998) have argued that the right hemisphere contains its own lexical processing system separate from the main reading system that operates in the left hemisphere. This right hemisphere system, they argue, can identify letters and words but is unable to name them. An ability able to gain access to the letter processing components of the right hemisphere system but not the letter processing components of the left hemisphere system would explain MS's ability to categorise but not name visually presented letters. An ability to access preserved left hemisphere letter processing mechanisms following auditory or haptic presentation would explain why she can name letters presented in other modalities. Such an account is consistent with ReyterLorenz and Baynes' (1992) conclusion that the right hemisphere of a collosotomy patient was unable to transfer information about letter identity from the right to the left hemisphere. It is also consistent with the fact that MS has a right hemianopia, and with what we know about the location of the lesions that are typically observed in pure alexia (Dejerine, 1892). Nevertheless, it is impossible to argue unequivocally for the right hemisphere account in the absence of anatomical information of this kind in the case of MS. To summarize, therefore, we believe that the case of MS suggests that representations of

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abstract identities of letters are either hemisphere speci?c or else they differ as a function of modality of presentation. Miozzo and Caramazza (1998) have recently suggested an alternative to the right hemisphere hypothesis wherein the right hemisphere contains representations of the visual forms of letters, but does not store abstract letter identities. These can only be accessed from the left hemisphere letter processing system. Such a hypothesis is unable to explain the pattern of performance observed in MS, however. If MS was accessing left hemisphere abstract letter representations when performing tasks such as cross case matching of visually presented letters then there would be no obvious way of explaining why her letter naming ability was so strongly affected by modality of presentation. It is also important to point out that MS appears to suffer from a qualitatively different type of letter processing impairment from that which is typically seen in letter-by-letter reading. For example, the letter-by-letter reader (SP) reported by Perri, Bartolomeo and Silveri (1996) was much better than MS at naming visually presented letters (70% correct for lowercase letters, 80% correct for uppercase letters). However, unlike MS, SP was impaired at cross-case matching of visually presented letters, and the letter misidenti?cations that he made when naming letters appeared to be based on physical similarity to the target letter. When SP did correctly recognise the abstract identity of a letter, there was no evidence of an additional letter-naming de?cit. This pattern of performance suggests that the source of SP's letter processing problem was a dif?culty in accessing the abstract identity of visually presented letters, whereas MS's letter processing problem re?ects a dif?culty at the level of letter name retrieval. 2 It does not appear to be the case, therefore, that MS is unable to read words letter-by-letter simply because her letter processing skills are more severely impaired than is typically observed in letter-by-letter readers. It appears to be much more likely that it is MS's total inability to name visually presented letters that prevents her from reading letter-by-letter. 3 In conclusion, therefore, the letter processing ability of MS presents an interesting dissociation between that of both the pure alexic GV (Miozzo & Caramazza, 1998) and the letter-by-letter reader SP (Perri et al., 1996). Although GV and MS are equally poor at naming letters, MS is much better at identifying them at an abstract level. By contrast, SP is better at naming letters than MS letters despite being less accurate at recognising their abstract identity. It has often been suggested (Behrmann et al., 1998) that lexical processing impairments in alexia are closely related to letter level impairments. It would
It is interesting to note that the letter processing abilities of the deep dyslexic patient GR (Marshall & Newcombe, 1966) were much more similar to those of MS than SP. GR was only 50% correct on average at letter naming but was 100% correct on cross-case matching. If deep dyslexia re?ects right hemisphere reading (Coltheart, 2000), then the performance of GR is consistent with the conclusion that the right hemisphere can produce the abstract identity of visually presented letters more successfully than it can produce their name. 3 Although it may be the reason why she is unable to read words letter-by-letter, we would certainly not wish to claim that MS's fundamental problem in reading words is a consequence of her inability to name letters. The fact that she was only able to make correct visual lexical decisions about 9/24 real words suggests that she is unable to use the information that she can access about abstract letter identities to reliably activate lexical level representations for visually presented words. Her inability to read does not appear to be a consequence of any loss of lexical knowledge, however, because when letter names were presented auditorily to MS, she performed very much better at identifying words.
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be extremely useful if future research were to investigate whether the differences between the letter processing impairments observed in MS and SP will also be revealed in future examinations of alexic patients who differ in the ability to read words letter-byletter. References
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