Quarterly Journal of Experimental Psychology
ISSN: 0033-555X (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/pqje19
Aphasia, dyslexia and the phonological coding of written words K. E. Patterson & A. J. Marcel To cite this article: K. E. Patterson & A. J. Marcel (1977) Aphasia, dyslexia and the phonological coding of written words, Quarterly Journal of Experimental Psychology, 29:2, 307-318, DOI: 10.1080/14640747708400606 To link to this article: http://dx.doi.org/10.1080/14640747708400606
Published online: 29 May 2007.
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Date: 05 November 2015, At: 18:01
Quarterly Journal of Experimental Psychology (1977) 29, 307-3 18
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APHASIA, DYSLEXIA AND THE PHONOLOGICAL CODING OF WRITTEN WORDS K. E. PATTERSON AND A. J. MARCEL M.R.C. Applied Psychology Unit, 15 Chaucer Road, Cambridge CB2 zEF, U.K. A possible account of the reading difficulty of certain aphasic-dyslexic patients includes the notion that they are impaired in translating the written word into a phonological code via grapheme-phoneme conversion rules. This notion was tested in two experiments, both utilizing orthographically regular non-words (like dake) as stimuli. The first experiment provides an analysis of two patients’ (largely successful) attempts to repeat non-words, and their (almost totally unsuccessful) attempts to read them. Second, in a lexical decision task (is this written letter-string a word or not?), the finding that normals are slowed by non-words homophonic with real words (like pore) was replicated using a modified technique. This effect, attributable to phonological coding, was not shown by the patients. At the same time, their ability to discriminate between words and non-words was essentially intact. Consideration was given to mechanisms which might underlie such patients’ correct and erroneous readings of words and non-words.
Introduction Individuals with acquired aphasia, resulting from cerebral damage, often display reading disabilities. One particularly interesting form of such dyslexia has been termed “deep” (Marshall and Newcombe, 1973) or “phonemic” (Shallice and Warrington, 1975) dyslexia. When patients with this syndrome are asked to read individual words aloud, their performance can be characterized as follows : (I) some words, primarily nouns and adjectives high in imageability/concreteness, are read correctly; (2) some words, and especially function words and abstract words, receive no overt response at all; and (3) some words evoke paralexic errors, where the relationship between stimulus and response can be further classified as visual (e.g. origin-“organ”), derivational (e.g. courage-“courageous”), or semantic (e.g. dream-“sleep”). These paralexic responses are especially intriguing, because they indicate that the written word is providing some appropriate information to the patient’s language system, despite the failure of one or more processes crucial to the production of the correct response. Errors such as these are potentially explicable in terms of a model of normal word recognition and production like Morton’s (1968, 1969) logogen system. T h e features of the model of particular relevance here are its assumptions (a) that in the 307
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K. E. PATTERSON AND A. J. MARCEL
process of visual analysis, logogens (or lexical entries) for words graphically similar
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to a presented word are activated to some extent; (b) that as a result of semantic
interpretation, logogens for words semantically similar to the presented item are also activated; and (c) that the critical threshold of activation, where the word becomes available as a response, varies from word to word. An account of paralexic errors requires only the further assumption that, in a phonemic dyslexic patient, threshold differences between words or classes of words may be abnormally augmented. A word which is visually similar or semantically related to the presented item (and especially one related in both ways, as in the case of a derivational connection like courage-“courageous”) and which has a substantially lower threshold than the correct word may then be expected as a paralexic error. Since the normal logogen system is characterized by differential thresholds for various words, such reading errors could in principle occur in the undamaged brain. Normal readers do make paralexic errors in reading text (Morton, 1964; Kolers, 1970) and even in reporting unrelated or single words under conditions of patternmasked tachistoscopic exposure (Allport, in press ; Marcel, 1974). More importantly, however, there may be additional processes in normal reading which function to suppress such errors. One candidate for an error-suppressing process in reading is grapheme-phoneme conversion. A non-lexical route to phonology is necessary to account for our ability to pronounce orthographically regular non-words like dube and indeed to pronounce new words. If, in reading, the graphic analysis of a word is subjected to such a conversion process, the resulting phonological representation may provide a confirmatory source of evidence on the identity of a word. One plausible hypothesis regarding phonemic dyslexia is that it entails an impaired ability to obtain a phonological code for a written word via this non-lexical route. This suggestion has in fact been made by Marshall and Newcombe (1973) and by Shallice and Warrington (1975) but has received little direct evaluation. T h e current research involved two experiments designed to test this hypothesis. Both experiments utilize orthographically regular non-words because actual words, which almost certainly possess both lexical and non-lexical routes to phonology, make it difficult to isolate the operation of one route. T h e first experiment tested the ability of phonemic dyslexics to read orthographically regular non-words. T h e second experiment involved a lexical decision task, where the subject decides whether a printed letter string is a word or not. This paradigm has played a prominent role in experimental considerations of a controversy regarding the involvement of grapheme-phoneme conversion in normal reading. We will not attempt to evaluate this issue (see Coltheart, Davelaar, Jonasson and Besner, in press ; and Meyer, Schvaneveldt and Ruddy, 1974, for discussions). However, one result from the controversy is particularly germane here: in the lexical decision task, normal subjects take longer to say “no” to a non-word which sounds exactly like a real word (e.g. stane) than to a non-word which does not sound exactly like any word (e.g. stame) (Coltheart et al, in press; Rubenstein, Lewis and Rubenstein, 1971). This result would seem to arise from phonological coding, accessing any lexical entry having equivalent phonology. It consequently suggests a method of investigating that coding system in dyslexic patients. If these patients are impaired
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in grapheme-phoneme conversion, the prediction follows that their performance in lexical decision should be unaffected by the phonological status .of non-words.
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Description of patients T h e patients tested in this research were two severely aphasic males who come to Addenbrooke’s Hospital, Cambridge for speech therapy on a regular out-patient basis. D. E. (born in 1954) had a motor-scooter accident in 1970; a bilateral carotid angiogram several days after the accident revealed almost total occlusion of the left internal carotid artery. He currently exhibits a moderate right hemiplegia, but no other physical abnormalities. He holds a full-time job as a store-keeper for a manufacturing company. Administration of the Boston Diagnostic Aphasia Test (Goodglass and Kaplan, 1972) in 1975 produced an aphasia severity rating of z (on a scale from o to 5, where o represents no usable speech and 5 corresponds to minimal discernable speech handicap), and a profile very typical of Broca’s aphasia. Thus, his speech is almost exclusively content words, maximum phrase length is three words, the range of grammatical form used is quite limited, and melodic line is virtually absent. His auditory comprehension, as measured by the Boston Test, is sub-normal but only mildly so. T h e only respect in which his speech deviates from the typical Broca profile described by Goodglass and Kaplan is articulatory agility, on which he scored slightly higher than is typical for this classification. P. W. (born in 1908) is an ex-civil servant who suffered a cerebrovascular accident in 1965. H e displays a severe right hemiplegia, and very limited expressive speech. On the Boston Diagnostic Test in 1975, P.W. received an aphasia severity rating of I ;his speech profile was reasonably standard for Broca’s aphasia, though his auditory comprehension score was somewhat lower than is usual in this diagnostic category.
TABLE I Tests of language function Number correct Test
Token test (De Renzi) Object naming Object naming from description Reading individual letters Reading words (Schonell) Spelling words (Schonell)
D.E.
P.W
10115
4115
14/15
14/15
4
15
10126 361100 o/roo
8115
8/26 37/100 011 00
The results of further tests of language function for both patients are shown in Table I, and will be described for D.E. first. A shortened form (from Warrington, Logue and Pratt, 1971) of the Token Test (De Renzi and Vignolo, 1962), which measures auditory comprehension with instructions such as “Before touching the brown circle, pick up the red triangle”, corroborated the result from the Boston
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K. E. PATTERSON AND A. J. MARCEL
Aphasia Test for D.E. : his comprehension is sub-normal but not severely impaired. T h e next two tests (also from Warrington, 1975 and Warrington et al., 1971)show that D.E.’s ability to name common objects is essentially normal (his one error was on a thimble, which he named “needle”), and his naming from description (e.g. “What is the name of the bird that flies at night and hoots?”) is only moderately impaired. Note that this latter test taps both naming ability and auditory comprehension. His reading of individual letters, tested in random order, was very poor: he managed only A through E, I and W through 2 (a serial position effect?). On the Schonell (1942) graded word reading test, 35 of his 36 correct responses came from the first and easier half of the list. l ’ h e Token Test showed badly disrupted auditory comprehension for P.W., though he was somewhat more successful at the level of comprehension required by naming from description (which does not depend so heavily on precise syntactic interpretation). His naming of common objects was adequate, though slow; and his performance on reading both letters and words (Schonell) was quite similar to the pattern already described for D.E. Both patients, and in particular P. W., indicated “recognition” of some of the letters which they were unable to read aloud, by responding with a word or name which begins with the presented letter. An attempt was made to administer the Schonell oral spelling test to these patients, but neither one could spell the simplest of words in this manner. T h e Schonell reading test indicates that word frequency is one determinant of reading performance for these patients. Previous work on phonemic dyslexia, such as studies of K.F. by Shallice and Warrington (1975) and of G.R. by Marshall and Newcombe (1973) and Richardson (1975), suggests that imageability ratings of words should also affect probability of correct reading. Using both the Colorado Concreteness and Imagery Norms (1973) and the Paivio, Yuille and Madigan norms (1968), 38 words were selected, primarily nouns plus a few adjectives. Half of the words were high in imageability or I (on a scale from I to 7, mean I = 5-23, with a range of 4.68 to 5.80) and half were low (mean I = 2.97, with a range of 2-30 to 3-43). T h e two sets were balanced as closely as possible for mean word length (high I: 6.2 letters; low I: 5-8 letters) and for mean concreteness ratings: (high I: 3.79; low I : 3.65 ; also on a scale from I to 7). An unsuccessful attempt was made to balance the sets for frequency of usage as well. However, the direction of the frequency difference should work against any effect of imageability, since mean occurrences per million (Kucera and Francis, 1967) were 47-4 for the high I words and 135-3 for the low I words. T h e 38 words were typed individually on 3 x 5-in cards, in lower case, and were presented in random order to the patients to read aloud. T h e top section of Table I1 shows that imageability ratings are a very good predictor of reading peformance for both D.E. and P.W. Performance on this list can also serve to provide a picture of these patients’ reading errors, which are delineated in the lower section of Table 11. D.E.’s paralexic errors were mostly derivational or visual. On this particular list of words, he made no errors which were purely semantic in nature (i.e., without a visual component), though he has done so on other occasions (e.g. sife-“plot”; debt-“buy”). For P.W., on the other hand, the largest group of paralexic responses involved a semantic relationship to the target word. Neither
Derivational Visual Semantic Visual and semantic Paraphasic
ERRORS 0missions
High imageability Low imageability
CORRECT
24138
2
3
0
5
8
6
14/38
xz/rg 2/19
Number
Examples
amount-‘‘account”; incident-“accident” disaster-“like danger, airplane, crashed”
gain ;reason edition-“editor”; warmth-‘‘warm’’ origin-“organ” ;patent-“patient”
lecture; marriage event; scene
D.E.
24/38
4
I
I1
I
5
2
14/38
4/19
10/19
Number
P.W. Examples
phase ;reality danger-“dangerous” ; grown-“growing” gain-“grain” edition-“journal”; fact-“truth” incident-“accident” event-“athletics the same”
drawla; happy excuse; patent
Reading performance on words varying in imageability
TABLE I1
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K. E. PATTERSON AND A. J. MARCEL
patient produced a neologistic response, and indeed almost never does so. It should be noted that while some of the errors labelled visual also bear an acoustic similarity to the target word, the label of visual seems appropriate: errors often show visual similarity with little acoustic similarity (e.g. agony-“anger”) but never the reverse (as would be so if “loose” were a response to juice). As an addendum to the clinical description, it is perhaps worth mentioning that although these two patients display similar patterns of aphasia, Marshall and Newcombe (1973) and Shallice and Warrington (1975) have described phonemic dyslexic patients with different patterns of aphasic symptoms. Thus, while phonemic dyslexia almost certainly occurs only in the context of more general language impairment, at present there is no clear association between this syndrome and a specific type of aphasia.
Experiment I Method Two sets of orthographically regular non-words (RNW’s) were prepared, each consisting of 50items 3-6 letters in length, all single-syllable, all easily pronounceable by a normal person (see below). One set, for use with auditory presentation, contained only non-words which do not sound exactly like any real word in the English language (e.g. dake, widge, jub). T h e other set, for use with visual presentation, contained 25 of the 5 0 in the first set, plus 25 each of which sounds exactly like a real word (e.g. t o m , flore, stane). Part I of the test was a repeating task. Each one of the 50 RNW’s in set I was read aloud to the patient, following instructions to “repeat exactly what I say”. They were told that the items were non-words. Part 2 of the test, which took place several weeks after part I , was a reading task. The patient was given the 5 0 RNW’s in set 2, printed in lower case on two sheets and told: “Although these items are not words, it is possible to read them aloud, to pronounce them. Please try to read them, or to guess what you think they might sound like”. Eight normal subjects (of assorted sex, age and level of verbal skills) at the Applied Psychology Unit were given the 50 non-words in set z to read. None of them made what could reasonably be called an error. There were differences of pronunciation (e.g., toun was pronounced “town” by some and “toon” by others); and one subject made several initial slips which he then corrected (e.g. plosh-“splosh, no that’s plosh”). It was quite apparent that all the normals, even those who found the task puzzIing, were able to read the non-words without difficulty. It seemed unnecessary to test the ability of normals to repeat non-words.
Results and discussion T h e basic result of Experiment I can be seen in the per cent column of Table 111, and can be summarized in one sentence: these patients can repeat non-words but they cannot read them. This conclusion is reinforced by the denominator values in the number column of Table 111. T h e patients found the repeating task easy (though puzzling) to do, and completed it without hesitation. They found the reading task extremely difficult, even aversive ;they responded very slowly if at all ; and although neither refused to do the task, they were not forced to complete it, T h e importance of the patients’ success in part I lies mainly in its implications for their failure in part 2. That is, their inability to read non-words is neither (a)
PHONOLOGICAL CODING I N DYSLEXIA
313
TABLE I11 Performance on regular non-words Per cent D.E. P.W.
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Auditory Correct Word errors input (repeating)
76
74
Number D.E. P.W.
38/50 12/50
Non-word errors Omissions Visual Correct input Word errors (reading) Non-word errors Omissions
3/50
Examples dube, plosh, filk, widge duke-“dig” ; jub-“job” hort-“court” ;jleep“sleep” seb-“steb” ; tiW‘stib”
0150 I0
0
3/30 I 8/30
430 9/30
oj20 8/20
toun, jlore, wurk dake-“drake” ; sprude“spade” rud-“naughty” glem--“jewel”
0/20 12/20
a physical inability to produce those sounds, nor (b) an inability (or unwillingness) ever to produce nonsense. Performance in part I was clearly not perfect, and even for repetition these patients show a definite word advantage: they were tested on repeating a set of 50 single-syllable words, and both patients showed 100% correct repetition of words. They also showed a word bias in the non-word task, in that their incorrect responses (several examples of which are given in Table 111) were predominantly words. Note that there were no failures to respond. I n the reading task, the general inclination of both patients was to give no response. T h e fact that D.E. produced a larger proportion of word errors than P.W. probably reflects only his greater susceptibility to the experimenter’s encouragement to make some response. Alternatively, or additionally, this difference between the two patients may be related to the fact that in reading words, D.E. makes more visual errors than P.W. T h e critical result in any case is that there were only two types of response: omissions and real words. While the normal person can operate non-lexically with written material, the phonemic dyslexic seems restricted to lexical treatment of such input. Most of the word errors, for both patients, bore a simple graphic similarity to the stimulus item; some additional T h e examples in Table 111 examples are cit-“city” ;frute-“flute” ;gat-“gate”. are given to indicate (a) that letters are both added and deleted to produce responses; and (b) that even in attempting to read non-words, the patients’ responses can contain both visual and semantic components. One further example seems worth presenting. D.E. produced four responses to one stimulus item (rair“chair, hair, rain, air”), which must represent a substantial proportion of the lexical items which are visually similar to rair. T h e experimenter then suggested saying “air” with the first sound of “rain” added on to the front; but D.E. simply laughed and said “no”.
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K. E. PATTERSON AND A. J. MARCEL
T h e results of the reading task suggest that these patients have a major deficit in the ability to convert a written stimulus into a phonological code via a non-lexical set of conversion rules. It seems likely that the failure is in obtaining the phonological code proper and not just in accomplishing its articulation. First, the patients can articulate these non-words given auditory presentation. Second, after a patient had failed to read a non-word, the experimenter often produced it for him, asking “Does it look as if it might sound like -?” Neither patient ever answered this question in the affirmative. It is difficult to be certain, but even the three correct readings of non-words by D.E. were probably obtained through access of the graphically-similar lexical entry or logogen rather than through application of conversion rules. This interpretation implies that the only non-word responses which could be correct, though spuriously so, would be to items which are homophonic with real words. Further, only homophonic non-words which are also graphically similar to their lexical counterparts could yield “correct” readings. Thus, while toun, jlore, and wurk might (and did for D.E.) produce “correct” responses, we predict that phude, korse and sprade should never do.
Experiment 11 Experiment I was interpreted as suggesting that the non-lexical route from graphemes to phonemes is essentially inoperative in patients with phonemic dyslexia. Experiment I, however, required the patient not only to convert graphemes to phonemes, but then also to produce those phonemes; and while unlikely, it is still possible that the difficulty arose alternatively or additionally at the articulation stage. Experiment I1 employs the lexical decision paradigm, where phonological conversion seems to occur in normal subjects, but the overt response is not the articulation of that phonological code. T h e typical datum in a lexical decision experiment is the reaction time to individual items. Since the conditions under which patients were tested precluded such fine-grained measurement, we measured the time period required for lexical decisions on whole lists of letter strings.
Method The 10control subjects for this experiment included two students, four young enlisted men from the Navy, and four members of the Applied Psychology Unit subject panel. The stimulus materials consisted of (a) a set of 3-6-letter, single-syllable, familiar nouns, verbs and adjectives (minimum frequency of occurrence 10 per million, Kucera and Francis, 1967) and (b) a set of 3-6-letter single-syllable non-words like those described in Experiment I, that is orthographically regular and easily pronounceable by a normal person. Half of the non-words were homophonic with real words (e.g. stane, frute) and half were non-homophonic (duke, selt). T h e test began with a practice list of 28 letter strings, consisting of 14words, seven homophonic non-words, and seven non-homophonic non-words. This was followed by four test lists, each with 34 letter strings: two lists each contained 17 words and 17 homophonic non-words, while the other two lists each contained 17 words and 17 non-homophonic non-words. Each list was printed (lower case) in two columns on a sheet of paper, with randomised order of words and non-words. Each subject was tested individually, and was instructed simply to respond “yes” if he recognised a letter string as a real word and “no” if he did not. He was asked to move through each list steadily, not pausing between items and not going back to an item even if he thought he had made a mistake. The response period for each list was timed (to the nearest 7
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PHONOLOGICAL CODING IN DYSLEXIA
half second) with a stop watch, starting when the experimenter handed the subject the list and said “begin” and terminating as soon as the subject had said “yes” or “no” to the final item on the list. All subjects were tested on the two types of lists in alternation, half beginning with one type and half with the other. Both patients had been given some experience with the lexical decision task several weeks prior to the collection of the data presented here.
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Results and discussion
All subjects, both normal and aphasic, performed the lexical decision task with reasonable accuracy; the patients, in fact, made no more errors than several of the normals. For all subjects, false positive errors (“yes” to a non-word) were more frequent than miss errors (“no” to a real word), which is not surprising given familiar words and orthographically regular non-words. Over all four lists, D.E. had three misses, P.W. had none; two control subjects had five and three misses each, and the remaining controls had none.
TABLE IV Time (s) and false positives (number) for the two types of lists in the lexical decision task. Values in parentheses for controE group are standard deviations Lists with homophonic Lists with nonhomophonic non-words non-words TIME Control mean D.E. P.W. FALSE POSITIVES Control mean D.E. P.W.
25.85 (7‘55) 33‘50 39.00
27.88 (7.71) 30’75 38’75
Difference score +2’03 (0.49) -2’75 -0.25
1.55 (1.82)
+0.70
5
4
-1
4
I
-3
0.85
(1.42)
(0.20)
~~
Table IV presents, for the patients individually and for the controls as a group, the response times and numbers of false positives for the two types of lists, and difference scores between the two types of lists. Since each subject was tested on two lists of each type, the values presented for the patients and used in the statistical analysis for the normals are averages of performance on these two lists. Looking first at the control data, we see that lexical decision was significantly slower on lists with homophonic non-words than on lists with non-homophonic non-words, t(9) = 4.12,P (0.005. Control subjects also made more false positive errors to homophonic non-words than to non-homophonic non-words, t(9) = 3-5,P
ISSN: 0033-555X (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/pqje19
Aphasia, dyslexia and the phonological coding of written words K. E. Patterson & A. J. Marcel To cite this article: K. E. Patterson & A. J. Marcel (1977) Aphasia, dyslexia and the phonological coding of written words, Quarterly Journal of Experimental Psychology, 29:2, 307-318, DOI: 10.1080/14640747708400606 To link to this article: http://dx.doi.org/10.1080/14640747708400606
Published online: 29 May 2007.
Submit your article to this journal
Article views: 162
View related articles
Citing articles: 163 View citing articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=pqje19 Download by: [Chinese University of Hong Kong]
Date: 05 November 2015, At: 18:01
Quarterly Journal of Experimental Psychology (1977) 29, 307-3 18
Downloaded by [Chinese University of Hong Kong] at 18:01 05 November 2015
APHASIA, DYSLEXIA AND THE PHONOLOGICAL CODING OF WRITTEN WORDS K. E. PATTERSON AND A. J. MARCEL M.R.C. Applied Psychology Unit, 15 Chaucer Road, Cambridge CB2 zEF, U.K. A possible account of the reading difficulty of certain aphasic-dyslexic patients includes the notion that they are impaired in translating the written word into a phonological code via grapheme-phoneme conversion rules. This notion was tested in two experiments, both utilizing orthographically regular non-words (like dake) as stimuli. The first experiment provides an analysis of two patients’ (largely successful) attempts to repeat non-words, and their (almost totally unsuccessful) attempts to read them. Second, in a lexical decision task (is this written letter-string a word or not?), the finding that normals are slowed by non-words homophonic with real words (like pore) was replicated using a modified technique. This effect, attributable to phonological coding, was not shown by the patients. At the same time, their ability to discriminate between words and non-words was essentially intact. Consideration was given to mechanisms which might underlie such patients’ correct and erroneous readings of words and non-words.
Introduction Individuals with acquired aphasia, resulting from cerebral damage, often display reading disabilities. One particularly interesting form of such dyslexia has been termed “deep” (Marshall and Newcombe, 1973) or “phonemic” (Shallice and Warrington, 1975) dyslexia. When patients with this syndrome are asked to read individual words aloud, their performance can be characterized as follows : (I) some words, primarily nouns and adjectives high in imageability/concreteness, are read correctly; (2) some words, and especially function words and abstract words, receive no overt response at all; and (3) some words evoke paralexic errors, where the relationship between stimulus and response can be further classified as visual (e.g. origin-“organ”), derivational (e.g. courage-“courageous”), or semantic (e.g. dream-“sleep”). These paralexic responses are especially intriguing, because they indicate that the written word is providing some appropriate information to the patient’s language system, despite the failure of one or more processes crucial to the production of the correct response. Errors such as these are potentially explicable in terms of a model of normal word recognition and production like Morton’s (1968, 1969) logogen system. T h e features of the model of particular relevance here are its assumptions (a) that in the 307
308
K. E. PATTERSON AND A. J. MARCEL
process of visual analysis, logogens (or lexical entries) for words graphically similar
Downloaded by [Chinese University of Hong Kong] at 18:01 05 November 2015
to a presented word are activated to some extent; (b) that as a result of semantic
interpretation, logogens for words semantically similar to the presented item are also activated; and (c) that the critical threshold of activation, where the word becomes available as a response, varies from word to word. An account of paralexic errors requires only the further assumption that, in a phonemic dyslexic patient, threshold differences between words or classes of words may be abnormally augmented. A word which is visually similar or semantically related to the presented item (and especially one related in both ways, as in the case of a derivational connection like courage-“courageous”) and which has a substantially lower threshold than the correct word may then be expected as a paralexic error. Since the normal logogen system is characterized by differential thresholds for various words, such reading errors could in principle occur in the undamaged brain. Normal readers do make paralexic errors in reading text (Morton, 1964; Kolers, 1970) and even in reporting unrelated or single words under conditions of patternmasked tachistoscopic exposure (Allport, in press ; Marcel, 1974). More importantly, however, there may be additional processes in normal reading which function to suppress such errors. One candidate for an error-suppressing process in reading is grapheme-phoneme conversion. A non-lexical route to phonology is necessary to account for our ability to pronounce orthographically regular non-words like dube and indeed to pronounce new words. If, in reading, the graphic analysis of a word is subjected to such a conversion process, the resulting phonological representation may provide a confirmatory source of evidence on the identity of a word. One plausible hypothesis regarding phonemic dyslexia is that it entails an impaired ability to obtain a phonological code for a written word via this non-lexical route. This suggestion has in fact been made by Marshall and Newcombe (1973) and by Shallice and Warrington (1975) but has received little direct evaluation. T h e current research involved two experiments designed to test this hypothesis. Both experiments utilize orthographically regular non-words because actual words, which almost certainly possess both lexical and non-lexical routes to phonology, make it difficult to isolate the operation of one route. T h e first experiment tested the ability of phonemic dyslexics to read orthographically regular non-words. T h e second experiment involved a lexical decision task, where the subject decides whether a printed letter string is a word or not. This paradigm has played a prominent role in experimental considerations of a controversy regarding the involvement of grapheme-phoneme conversion in normal reading. We will not attempt to evaluate this issue (see Coltheart, Davelaar, Jonasson and Besner, in press ; and Meyer, Schvaneveldt and Ruddy, 1974, for discussions). However, one result from the controversy is particularly germane here: in the lexical decision task, normal subjects take longer to say “no” to a non-word which sounds exactly like a real word (e.g. stane) than to a non-word which does not sound exactly like any word (e.g. stame) (Coltheart et al, in press; Rubenstein, Lewis and Rubenstein, 1971). This result would seem to arise from phonological coding, accessing any lexical entry having equivalent phonology. It consequently suggests a method of investigating that coding system in dyslexic patients. If these patients are impaired
309
PHONOLOGICAL CODING IN DYSLEXIA
in grapheme-phoneme conversion, the prediction follows that their performance in lexical decision should be unaffected by the phonological status .of non-words.
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Description of patients T h e patients tested in this research were two severely aphasic males who come to Addenbrooke’s Hospital, Cambridge for speech therapy on a regular out-patient basis. D. E. (born in 1954) had a motor-scooter accident in 1970; a bilateral carotid angiogram several days after the accident revealed almost total occlusion of the left internal carotid artery. He currently exhibits a moderate right hemiplegia, but no other physical abnormalities. He holds a full-time job as a store-keeper for a manufacturing company. Administration of the Boston Diagnostic Aphasia Test (Goodglass and Kaplan, 1972) in 1975 produced an aphasia severity rating of z (on a scale from o to 5, where o represents no usable speech and 5 corresponds to minimal discernable speech handicap), and a profile very typical of Broca’s aphasia. Thus, his speech is almost exclusively content words, maximum phrase length is three words, the range of grammatical form used is quite limited, and melodic line is virtually absent. His auditory comprehension, as measured by the Boston Test, is sub-normal but only mildly so. T h e only respect in which his speech deviates from the typical Broca profile described by Goodglass and Kaplan is articulatory agility, on which he scored slightly higher than is typical for this classification. P. W. (born in 1908) is an ex-civil servant who suffered a cerebrovascular accident in 1965. H e displays a severe right hemiplegia, and very limited expressive speech. On the Boston Diagnostic Test in 1975, P.W. received an aphasia severity rating of I ;his speech profile was reasonably standard for Broca’s aphasia, though his auditory comprehension score was somewhat lower than is usual in this diagnostic category.
TABLE I Tests of language function Number correct Test
Token test (De Renzi) Object naming Object naming from description Reading individual letters Reading words (Schonell) Spelling words (Schonell)
D.E.
P.W
10115
4115
14/15
14/15
4
15
10126 361100 o/roo
8115
8/26 37/100 011 00
The results of further tests of language function for both patients are shown in Table I, and will be described for D.E. first. A shortened form (from Warrington, Logue and Pratt, 1971) of the Token Test (De Renzi and Vignolo, 1962), which measures auditory comprehension with instructions such as “Before touching the brown circle, pick up the red triangle”, corroborated the result from the Boston
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Aphasia Test for D.E. : his comprehension is sub-normal but not severely impaired. T h e next two tests (also from Warrington, 1975 and Warrington et al., 1971)show that D.E.’s ability to name common objects is essentially normal (his one error was on a thimble, which he named “needle”), and his naming from description (e.g. “What is the name of the bird that flies at night and hoots?”) is only moderately impaired. Note that this latter test taps both naming ability and auditory comprehension. His reading of individual letters, tested in random order, was very poor: he managed only A through E, I and W through 2 (a serial position effect?). On the Schonell (1942) graded word reading test, 35 of his 36 correct responses came from the first and easier half of the list. l ’ h e Token Test showed badly disrupted auditory comprehension for P.W., though he was somewhat more successful at the level of comprehension required by naming from description (which does not depend so heavily on precise syntactic interpretation). His naming of common objects was adequate, though slow; and his performance on reading both letters and words (Schonell) was quite similar to the pattern already described for D.E. Both patients, and in particular P. W., indicated “recognition” of some of the letters which they were unable to read aloud, by responding with a word or name which begins with the presented letter. An attempt was made to administer the Schonell oral spelling test to these patients, but neither one could spell the simplest of words in this manner. T h e Schonell reading test indicates that word frequency is one determinant of reading performance for these patients. Previous work on phonemic dyslexia, such as studies of K.F. by Shallice and Warrington (1975) and of G.R. by Marshall and Newcombe (1973) and Richardson (1975), suggests that imageability ratings of words should also affect probability of correct reading. Using both the Colorado Concreteness and Imagery Norms (1973) and the Paivio, Yuille and Madigan norms (1968), 38 words were selected, primarily nouns plus a few adjectives. Half of the words were high in imageability or I (on a scale from I to 7, mean I = 5-23, with a range of 4.68 to 5.80) and half were low (mean I = 2.97, with a range of 2-30 to 3-43). T h e two sets were balanced as closely as possible for mean word length (high I: 6.2 letters; low I: 5-8 letters) and for mean concreteness ratings: (high I: 3.79; low I : 3.65 ; also on a scale from I to 7). An unsuccessful attempt was made to balance the sets for frequency of usage as well. However, the direction of the frequency difference should work against any effect of imageability, since mean occurrences per million (Kucera and Francis, 1967) were 47-4 for the high I words and 135-3 for the low I words. T h e 38 words were typed individually on 3 x 5-in cards, in lower case, and were presented in random order to the patients to read aloud. T h e top section of Table I1 shows that imageability ratings are a very good predictor of reading peformance for both D.E. and P.W. Performance on this list can also serve to provide a picture of these patients’ reading errors, which are delineated in the lower section of Table 11. D.E.’s paralexic errors were mostly derivational or visual. On this particular list of words, he made no errors which were purely semantic in nature (i.e., without a visual component), though he has done so on other occasions (e.g. sife-“plot”; debt-“buy”). For P.W., on the other hand, the largest group of paralexic responses involved a semantic relationship to the target word. Neither
Derivational Visual Semantic Visual and semantic Paraphasic
ERRORS 0missions
High imageability Low imageability
CORRECT
24138
2
3
0
5
8
6
14/38
xz/rg 2/19
Number
Examples
amount-‘‘account”; incident-“accident” disaster-“like danger, airplane, crashed”
gain ;reason edition-“editor”; warmth-‘‘warm’’ origin-“organ” ;patent-“patient”
lecture; marriage event; scene
D.E.
24/38
4
I
I1
I
5
2
14/38
4/19
10/19
Number
P.W. Examples
phase ;reality danger-“dangerous” ; grown-“growing” gain-“grain” edition-“journal”; fact-“truth” incident-“accident” event-“athletics the same”
drawla; happy excuse; patent
Reading performance on words varying in imageability
TABLE I1
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K. E. PATTERSON AND A. J. MARCEL
patient produced a neologistic response, and indeed almost never does so. It should be noted that while some of the errors labelled visual also bear an acoustic similarity to the target word, the label of visual seems appropriate: errors often show visual similarity with little acoustic similarity (e.g. agony-“anger”) but never the reverse (as would be so if “loose” were a response to juice). As an addendum to the clinical description, it is perhaps worth mentioning that although these two patients display similar patterns of aphasia, Marshall and Newcombe (1973) and Shallice and Warrington (1975) have described phonemic dyslexic patients with different patterns of aphasic symptoms. Thus, while phonemic dyslexia almost certainly occurs only in the context of more general language impairment, at present there is no clear association between this syndrome and a specific type of aphasia.
Experiment I Method Two sets of orthographically regular non-words (RNW’s) were prepared, each consisting of 50items 3-6 letters in length, all single-syllable, all easily pronounceable by a normal person (see below). One set, for use with auditory presentation, contained only non-words which do not sound exactly like any real word in the English language (e.g. dake, widge, jub). T h e other set, for use with visual presentation, contained 25 of the 5 0 in the first set, plus 25 each of which sounds exactly like a real word (e.g. t o m , flore, stane). Part I of the test was a repeating task. Each one of the 50 RNW’s in set I was read aloud to the patient, following instructions to “repeat exactly what I say”. They were told that the items were non-words. Part 2 of the test, which took place several weeks after part I , was a reading task. The patient was given the 5 0 RNW’s in set 2, printed in lower case on two sheets and told: “Although these items are not words, it is possible to read them aloud, to pronounce them. Please try to read them, or to guess what you think they might sound like”. Eight normal subjects (of assorted sex, age and level of verbal skills) at the Applied Psychology Unit were given the 50 non-words in set z to read. None of them made what could reasonably be called an error. There were differences of pronunciation (e.g., toun was pronounced “town” by some and “toon” by others); and one subject made several initial slips which he then corrected (e.g. plosh-“splosh, no that’s plosh”). It was quite apparent that all the normals, even those who found the task puzzIing, were able to read the non-words without difficulty. It seemed unnecessary to test the ability of normals to repeat non-words.
Results and discussion T h e basic result of Experiment I can be seen in the per cent column of Table 111, and can be summarized in one sentence: these patients can repeat non-words but they cannot read them. This conclusion is reinforced by the denominator values in the number column of Table 111. T h e patients found the repeating task easy (though puzzling) to do, and completed it without hesitation. They found the reading task extremely difficult, even aversive ;they responded very slowly if at all ; and although neither refused to do the task, they were not forced to complete it, T h e importance of the patients’ success in part I lies mainly in its implications for their failure in part 2. That is, their inability to read non-words is neither (a)
PHONOLOGICAL CODING I N DYSLEXIA
313
TABLE I11 Performance on regular non-words Per cent D.E. P.W.
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Auditory Correct Word errors input (repeating)
76
74
Number D.E. P.W.
38/50 12/50
Non-word errors Omissions Visual Correct input Word errors (reading) Non-word errors Omissions
3/50
Examples dube, plosh, filk, widge duke-“dig” ; jub-“job” hort-“court” ;jleep“sleep” seb-“steb” ; tiW‘stib”
0150 I0
0
3/30 I 8/30
430 9/30
oj20 8/20
toun, jlore, wurk dake-“drake” ; sprude“spade” rud-“naughty” glem--“jewel”
0/20 12/20
a physical inability to produce those sounds, nor (b) an inability (or unwillingness) ever to produce nonsense. Performance in part I was clearly not perfect, and even for repetition these patients show a definite word advantage: they were tested on repeating a set of 50 single-syllable words, and both patients showed 100% correct repetition of words. They also showed a word bias in the non-word task, in that their incorrect responses (several examples of which are given in Table 111) were predominantly words. Note that there were no failures to respond. I n the reading task, the general inclination of both patients was to give no response. T h e fact that D.E. produced a larger proportion of word errors than P.W. probably reflects only his greater susceptibility to the experimenter’s encouragement to make some response. Alternatively, or additionally, this difference between the two patients may be related to the fact that in reading words, D.E. makes more visual errors than P.W. T h e critical result in any case is that there were only two types of response: omissions and real words. While the normal person can operate non-lexically with written material, the phonemic dyslexic seems restricted to lexical treatment of such input. Most of the word errors, for both patients, bore a simple graphic similarity to the stimulus item; some additional T h e examples in Table 111 examples are cit-“city” ;frute-“flute” ;gat-“gate”. are given to indicate (a) that letters are both added and deleted to produce responses; and (b) that even in attempting to read non-words, the patients’ responses can contain both visual and semantic components. One further example seems worth presenting. D.E. produced four responses to one stimulus item (rair“chair, hair, rain, air”), which must represent a substantial proportion of the lexical items which are visually similar to rair. T h e experimenter then suggested saying “air” with the first sound of “rain” added on to the front; but D.E. simply laughed and said “no”.
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T h e results of the reading task suggest that these patients have a major deficit in the ability to convert a written stimulus into a phonological code via a non-lexical set of conversion rules. It seems likely that the failure is in obtaining the phonological code proper and not just in accomplishing its articulation. First, the patients can articulate these non-words given auditory presentation. Second, after a patient had failed to read a non-word, the experimenter often produced it for him, asking “Does it look as if it might sound like -?” Neither patient ever answered this question in the affirmative. It is difficult to be certain, but even the three correct readings of non-words by D.E. were probably obtained through access of the graphically-similar lexical entry or logogen rather than through application of conversion rules. This interpretation implies that the only non-word responses which could be correct, though spuriously so, would be to items which are homophonic with real words. Further, only homophonic non-words which are also graphically similar to their lexical counterparts could yield “correct” readings. Thus, while toun, jlore, and wurk might (and did for D.E.) produce “correct” responses, we predict that phude, korse and sprade should never do.
Experiment 11 Experiment I was interpreted as suggesting that the non-lexical route from graphemes to phonemes is essentially inoperative in patients with phonemic dyslexia. Experiment I, however, required the patient not only to convert graphemes to phonemes, but then also to produce those phonemes; and while unlikely, it is still possible that the difficulty arose alternatively or additionally at the articulation stage. Experiment I1 employs the lexical decision paradigm, where phonological conversion seems to occur in normal subjects, but the overt response is not the articulation of that phonological code. T h e typical datum in a lexical decision experiment is the reaction time to individual items. Since the conditions under which patients were tested precluded such fine-grained measurement, we measured the time period required for lexical decisions on whole lists of letter strings.
Method The 10control subjects for this experiment included two students, four young enlisted men from the Navy, and four members of the Applied Psychology Unit subject panel. The stimulus materials consisted of (a) a set of 3-6-letter, single-syllable, familiar nouns, verbs and adjectives (minimum frequency of occurrence 10 per million, Kucera and Francis, 1967) and (b) a set of 3-6-letter single-syllable non-words like those described in Experiment I, that is orthographically regular and easily pronounceable by a normal person. Half of the non-words were homophonic with real words (e.g. stane, frute) and half were non-homophonic (duke, selt). T h e test began with a practice list of 28 letter strings, consisting of 14words, seven homophonic non-words, and seven non-homophonic non-words. This was followed by four test lists, each with 34 letter strings: two lists each contained 17 words and 17 homophonic non-words, while the other two lists each contained 17 words and 17 non-homophonic non-words. Each list was printed (lower case) in two columns on a sheet of paper, with randomised order of words and non-words. Each subject was tested individually, and was instructed simply to respond “yes” if he recognised a letter string as a real word and “no” if he did not. He was asked to move through each list steadily, not pausing between items and not going back to an item even if he thought he had made a mistake. The response period for each list was timed (to the nearest 7
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PHONOLOGICAL CODING IN DYSLEXIA
half second) with a stop watch, starting when the experimenter handed the subject the list and said “begin” and terminating as soon as the subject had said “yes” or “no” to the final item on the list. All subjects were tested on the two types of lists in alternation, half beginning with one type and half with the other. Both patients had been given some experience with the lexical decision task several weeks prior to the collection of the data presented here.
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Results and discussion
All subjects, both normal and aphasic, performed the lexical decision task with reasonable accuracy; the patients, in fact, made no more errors than several of the normals. For all subjects, false positive errors (“yes” to a non-word) were more frequent than miss errors (“no” to a real word), which is not surprising given familiar words and orthographically regular non-words. Over all four lists, D.E. had three misses, P.W. had none; two control subjects had five and three misses each, and the remaining controls had none.
TABLE IV Time (s) and false positives (number) for the two types of lists in the lexical decision task. Values in parentheses for controE group are standard deviations Lists with homophonic Lists with nonhomophonic non-words non-words TIME Control mean D.E. P.W. FALSE POSITIVES Control mean D.E. P.W.
25.85 (7‘55) 33‘50 39.00
27.88 (7.71) 30’75 38’75
Difference score +2’03 (0.49) -2’75 -0.25
1.55 (1.82)
+0.70
5
4
-1
4
I
-3
0.85
(1.42)
(0.20)
~~
Table IV presents, for the patients individually and for the controls as a group, the response times and numbers of false positives for the two types of lists, and difference scores between the two types of lists. Since each subject was tested on two lists of each type, the values presented for the patients and used in the statistical analysis for the normals are averages of performance on these two lists. Looking first at the control data, we see that lexical decision was significantly slower on lists with homophonic non-words than on lists with non-homophonic non-words, t(9) = 4.12,P (0.005. Control subjects also made more false positive errors to homophonic non-words than to non-homophonic non-words, t(9) = 3-5,P
