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PLATFORM SESSION 3: READING AND WRITING
Brain and Language 69, 389–398 (1999) Article ID brln.1999.2171, available online at http://www.idealibrary.com on
PLATFORM SESSION 3: READING AND WRITING Word-Centered Neglect Dyslexia and Aphasia in a Corrected Left-Hander
Gabriele Miceli and Rita Capasso Neurology, Catholic University, IRCCS S. Lucia, Rome, Italy
Introduction. Neuropsychological investigations of spatially specific reading disorders have led to the proposal that the early stages of word recognition involve three levels of representation. The retina-centered map represents the visual features of the stimulus in relation to their absolute position in the visual field, the stimulus-centered map represents specific letter shapes in relation to other letters in the stimulus, and the word-centered map consists of a graphemic description of the stimulus, in which abstract letter identities are ordered horizontally from left to right, centered with reference to the subject (Caramazza & Hillis, 1990). Subjects with damage to the wordcentered representation present with a well-defined neuropsychological profile: they read incorrectly letters in the contralesional half of the abstract representation, independent of stimulus orientation, case, and font, and make errors with comparable distribution in spelling. In addition, they also show neglect phenomena in purely visual tasks (e.g., line cancellation). The disorder is exceedingly rare, as only half a dozen cases are on record (see References). Consequently, both the theoretical implications and the anatomoclinical correlates of this deficit remain unclear. We report here on a new case of word-centered neglect dyslexia. Case history. SVE is a corrected left-hander with a 13th-grade education, who suffered from an ischemic right frontotemporoparietal lesion. He presents with anomia, ‘‘agrammatic’’ speech, and reduced verbal short-term memory; he also shows mild left neglect in line bisection and cancellation tasks. In reading aloud SVE, who reproduces correctly more words than pseudowords (70/92, 76.1% vs 10/45, 22.2%; χ 2 ⫽ 33.9; p ⬍ .001), makes errors almost exclusively (42/47, 89.4%) on stimulus-initial letters (grossa, big → ‘‘scossa,’’ quake; ravilo → ‘‘giovilo’’). Experimental study. Two-hundred forty 4-letter words were presented horizontally for 200 ms, in the left visual field, centered at the point of fixation, or in the right visual field (Fig. 16, upper half ). SVE read aloud correctly 389 0093-934X/99 $30.00
Copyright 1999 by Academic Press All rights of reproduction in any form reserved.
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FIG. 16. Reading aloud 4-letter words presented horizontally (upper half ) and vertically (lower left): occurrence of incorrectly reproduced letters in each position. The word CANE (dog) is presented as an example. Letters are shown as they appeared on the computer screen. 䊉, point of fixation, which always corresponded to the center of the computer screen. For horizontal presentation, words were located along the horizontal line passing at the center of the screen; for vertical presentation, two letters appeared above, and two below, the point of fixation.
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126/240 (52.5%), 144/240 (60%), and 155/240 (64.6%) words, respectively (χ 2 ⫽ 7.39; p ⬍ .05)—a result that suggests mild retinocentric damage. However, stimulus location was not the major determinant of performance in our subject, who systematically reproduced initial letters less accurately than final letters, independent of position in the visual field. For example, he made more errors on the first letter of words presented to the right of fixation (31.7% errors) than on the last letter of words presented to the left of fixation (4.6% errors), even though the former appeared in the ipsilesional hemifield and the latter in the contralesional hemifield (χ 2 ⫽ 57.5; p ⬍ .001). In addition, also irrespective of stimulus location, he performed with comparable accuracy on letters in the same within-word position. The same stimuli were presented vertically for 200 ms, to the left of the fixation point, at the fixation point, or to its right (Fig. 16, lower half ). SVE read aloud correctly 110/240 (45.8%), 150/240 (62.5%), and 151/240 (62.9%) words, respectively. Consistent with retinocentric neglect, he reproduced words presented to the left of fixation less accurately than words presented at the other two positions (p ⬍ .001). However, for each spatial location, SVE made more errors on the first than on any other letter ( p ⬍ .001 for all comparisons). Strikingly, this occurred even when words were presented vertically in the right (unaffected) visual field. Writing was severely impaired. Errors were often restricted to the initial letters of a target (pizza → . . . zza; barca, boat → circa, approximately). Overall, SVE managed to produce correctly 32/590.5 letters (5.4%) in the initial half and 265.5/590.5 letters (45%) in the final half of the response (χ 2 ⫽ 242.9; p ⬍ .001). SVE was presented for 200 ms with chimeric objects and asked to name the two halves of each chimera. He was comparably accurate when stimuli were presented in the left or in the right visual field, or at the center of the visual field (χ 2 ⫽ 1.63; p ⫽ n.s.), but systematically named the left half of a chimera less accurately than the right half (p ⬍ .001 for each location). This was true also for stimuli presented entirely in the right visual field. Discussion. The results produced by our subject can be easily summarized. Largely irrespective of stimulus orientation (horizontal, vertical) and absolute location in the visual field (left, center, right), SVE read aloud and wrote incorrectly word-initial letters and named incorrectly the left half of chimeric objects. This pattern of performance indicates damage to the word-centered representation. Thus, our subject adds to the extremely small number of cases in whom this disorder was documented. The observation of comparable performance on written words and chimeric objects suggests that this level of representation is shared by word and object recognition mechanisms. The relative contrast between marked neglect in tasks involving both visual and verbal processes, and the very mild disorder documented in purely visual tasks, presumably results from the interference of aphasia with wordcentered neglect.
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Retina-centered and stimulus-centered deficits are usually observed in right-handers after right-hemisphere damage (Hillis & Caramazza, 1995). In contrast, word-centered neglect has been reported both in left-handers and in dextrals, after damage to the right and to the left hemisphere (Barbut & Gazzaniga, 1987; Baxter & Warrington, 1983; Caramazza & Hillis, 1990; Hillis & Caramazza, 1995). SVE is a corrected left-hander with a righthemisphere lesion. Even though the anatomical basis of the word-centered representational level remains unclear, the observations reported in the various forms of neglect are consistent with the hypothesis that the levels of representation involved in visual word recognition are not only functionally, but also anatomically, distinct. REFERENCES Barbut, D., & Gazzaniga, M. 1987. Disturbances in conceptual space involving language and speech. Brain, 110, 1487–1496. Baxter, D. M., & Warrington, E. K. 1983. Neglect dysgraphia. Journal of Neurology, Neurosurgery and Psychiatry, 45, 1073–1078. Caramazza, A., & Hillis, A. E. 1990. Levels of representation, coordinate frames, and unilateral neglect. Cognitive Neuropsychology, 7, 391–445. Hillis, A. E., & Caramazza, A. 1995a. A framework for interpreting distinct patterns of hemispatial neglect. Neurocase, 1, 189–207. Hillis, A. E., & Caramazza, A. 1995b. Spatially specific deficits in processing graphemic representations in reading and writing. Brain and Language, 48, 263–308.
The Autonomy of Lexical Orthography: Evidence from Cortical Stimulation
Brenda Rapp,* Dana Boatman,† and Barry Gordon‡ *Cognitive Science Department, Johns Hopkins University; †Department of Neurology and Department of Otolaryngology, Johns Hopkins Medical School; and ‡Department of Neurology, Johns Hopkins Medical School, Baltimore, Maryland
Introduction In written language production, do we need to access the spoken form of a word in order to retrieve its spelling: meaning → lexical phonology → lexical orthography (obligatory phonological mediation)? Or, instead, is it possible to retrieve spelling directly from word meaning: meaning → lexical orthography (orthographic autonomy)? Clear evidence against the hypothesis of obligatory phonological mediation in written language production would be difficulty in retrieving the spoken forms of words for production in individuals who can, nonetheless, retrieve word spellings. A number of
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individuals with long-term deficits resulting from neurological injury have exhibited this pattern. Furthermore, in some of these studies it has been determined that the spoken naming deficits arose from difficulty in retrieving phonological lexical forms themselves rather than from damage to peripheral output mechanisms (Miceli et al., 1997; Rapp et al., 1997). Although this evidence favoring orthographic autonomy is extremely strong, one remaining concern is that direct links from word meaning to spelling are created only in situations in which individuals have suffered severe, long-term damage to spoken output processes. This investigation examines the possibility that the pattern of impaired spoken naming ⫹ preserved written naming might also be observed in the context of temporary, reversible deficits created through cortical electrical stimulation in individuals with normal language abilities. Such evidence would put to rest the concern that orthographic autonomy occurs only as an adaptation to chronic spoken language impairment. Case Studies Both of the subjects of this report suffered from chronic epilepsy and had subdural electrode arrays temporarily implanted for the purpose of localization of language functions and seizure foci prior to the surgical removal of the seizure foci. Case 1: LPN was a right-handed, 39-year-old female with 16 years of education. MRI revealed left mesial temporal sclerosis. WADA testing indicated left hemisphere dominance for language. LPN’s full scale (estimated) IQ was 117; she performed within normal limits on all language testing: naming (Boston), syntax, auditory comprehension (Token Test), oral word reading, and verbal fluency. Case 2: STS was a right-handed, 26-year-old male with 13 years of education. MRI results were normal. STS’s full scale (estimated) IQ was 103; he performed within normal limits on all language testing listed above. Methods Surgical procedures. Electrode arrays were surgically placed in the subdural space over the left hemisphere according to a preestablished protocol (Lesser et al., 1987). Arrays were composed of platinum disks, 3 mm in diameter, with a 2.3-mm-diameter exposed surface. Electrodes were 10 mm apart (center-to-center) in a rectangular pattern, embedded in medical-grade silastic. Electrical interference testing. Testing was initiated 2 days after surgical implantation of the electrode array. Cortical electrical interference was produced by 300-µs square-wave pulses of alternating polarity generated at a rate of 50 pulses per second through adjacent pairs of electrodes.
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Before testing each electrode site, the threshold current for afterdischarges or potential sensorimotor effects was established. If no afterdischarges or sensorimotor responses were present, the current was set to a maximal level of 15 mA. On stimulation trials, both stimulus and response were administered under electrical interference. The current remained activated for 5 s or until patients responded. Stimuli were presented approximately 1 s after current onset. The 5-s stimulus-response period was considered adequate in light of patients’ baseline response times without electrical interference. Cognitive testing. Patients were tested at each electrode pair on a range of tasks; we report on motor responses, spoken and written picture naming, and oral reading. The spoken and written picture naming tasks allow us to evaluate if subjects can proceed normally from picture recognition to meaning and then on to the retrieval of phonological and/or orthographic forms. Oral reading and motor responses allow us to evaluate the integrity of peripheral production mechanisms. Results Consistent with the hypothesis of orthographic autonomy, a pattern of impaired spoken picture naming accompanied by intact written picture naming was observed at multiple electrode sites for each subject. The observed deficits in spoken naming could not be attributed to interruption of the spoken production process at a peripheral level since tongue movements and oral reading were not affected. Furthermore, difficulty in spoken naming could not be attributed to a greater vulnerability of spoken naming mechanisms as STS exhibited the reverse dissociation of intact spoken naming and impaired written naming (Table 18).
TABLE 18 Percentage Correct across Various Tasks under Cortical Stimulation (T, Temporal Lobe; F, Frontal Lobe) Electrode site Subject LPN Posterior, midinferior T Posterior, midinferior T Posterior, basal T Subject STS Inferior, posterior F Inferior, anterior F Middle F Inferior, posterior F
Spoken naming
Written naming
Oral reading
Tongue, hand, finger mvmts
0% 25% 40%
100% 100% 100%
Mild slowing Mild slowing 100%
100% 100% 100%
20% 25% 100% 100%
100% 100% 20% 40%
100% 100% 100% 100%
100% 100% 100% 100%
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Conclusions The results of this study reveal that with electrical cortical stimulation techniques it is possible to interfere (at specific cortical locations) with the retrieval of lexical phonological forms without interfering with the retrieval of orthographic forms. These results allow us to conclude that the architecture of the naming system is organized so that orthographic lexical forms can be independently accessed for production without the mediating role of phonology. Furthermore, these results, obtained under conditions of temporary disruption of cortical activity, converge on conclusions reached from the study of subjects with long-term disruption. Thus, in addition to confirming the hypothesis of orthographic autonomy, these findings increase our confidence that the patterns of performance observed in subjects with long-term deficits may indeed legitimately form the basis for inferences about the functional organization of unimpaired cognitive systems. REFERENCES Lesser, R., Luders, H., Klem, G., et al. 1987. Extra-operative cortical functional localization in patients with epilepsy. Journal of Clinical Neuropsychology, 4, 27–53. Miceli, G., Benvegnu, B., Capasso, R., & Caramazza, A. 1997. The independence of phonological and orthographic lexical forms: Evidence from aphasia. Cognitive Neuropsychology, 14, 35–69. Rapp, B., Benzing, L., & Caramazza, A. 1997. The autonomy of lexical orthography. Cognitive Neuropsychology, 14, 71–104.
Grapheme-to-Lexeme Feedback in the Spelling System: Evidence from Dysgraphia
Michael McCloskey,* Paul Macaruso,† and Brenda Rapp* *Johns Hopkins University, Baltimore, Maryland; and †Community College of Rhode Island, Warwick, Rhode Island
Cognitive processes typically involve multiple levels of representation. For example, the process of writing a word may begin with a meaning to be expressed (e.g., domesticated animal that gives milk). From the semantic representation a lexical representation, or lexeme, may be activated (e.g., COW ). The lexeme representation may in turn activate abstract grapheme representations (C, O, W), which then activate letter-shape representations, and so on until the motor response is completed. A central issue concerns how the various levels of representation interact. For example, is the flow of information purely feedforward, as in (1), or is
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there multidirectional information flow, such that the various levels constrain one another via feedback as well as feedforward connections, as in (2)? Semantic ⇒ Lexeme ⇒ Grapheme
(1)
Semantic ⇔ Lexeme ⇔ Grapheme
(2)
This abstract focuses on interaction between lexeme and grapheme levels in writing. We present data from a brain-damaged patient as evidence for grapheme-to-lexeme feedback. Patient CM Patient CM is a 63-year-old man with a Ph.D. in electrical engineering. He worked as a researcher in a university laboratory until suffering a left middle cerebral artery CVA in 1986. CM’s language comprehension is mildly impaired (although single-word comprehension is intact), and both spoken and written language production are severely impaired. Experimental Study Over a 3-year period CM was presented with 3797 words in a writingto-dictation task. On each trial a word was dictated, CM repeated the word, then wrote the word, and then repeated it again. Although his repetition responses were uniformly correct, CM erred in spelling 1696 of the stimulus words (45%). Examples of his errors include half → halp, tip → tobe, and dignify → define. Two features of CM’s errors are relevant to our argument for grapheme-to-lexeme feedback: Letter intrusions and word errors. Letter intrusions. CM’s misspellings frequently included letters that did not appear in the correct spelling (e.g., the p in half → halp). The error corpus included 3354 of these intruded letters. As illustrated in the following trial sequence, many of the intruded letters were present in CM’s responses on one or more of the immediately preceding trials. For example, the intruded I in filter appears in three of the four prior responses (toples, wilten, bolt). Dictated stimulus casket blow wilt topple wept fit
CM’s written response casket bolt wilten toples wept filter
Analyses revealed that intruded letters appeared more often than expected by chance in responses on the five trials preceding the error. Additional analyses established that this letter persistence effect arose at a level of abstract grapheme representations and not at phonological or semantic levels or at
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more peripheral levels in the writing system (e.g., letter shape or graphomotor levels). The persistence effect may be interpreted by assuming that grapheme representations activated in spelling a word often remained active and consequently intruded on subsequent trials. Word errors. The second relevant feature of CM’s performance is that one-third of his errors (556/1696) took the form of words (e.g., dignify → define; arm → amber). Analyses revealed that like the error corpus as a whole, the word errors showed a strong letter persistence effect; that is, intruded letters in word responses were more likely than expected by chance to have appeared in preceding responses. For example, the intruded letters b and e in the arm → amber error occurred in the immediately preceding response (bench). Word errors could arise by chance at the grapheme level; that is, substitution or insertion of incorrect graphemes (e.g., insertion of a p after the s in sort) could produce a letter string that happened by chance to be a word (e.g., sport). We refer to such errors as chance word errors. However, word errors could also result from activation of the wrong word representation at the lexeme level (e.g., the lexeme AMBER when arm was dictated). We refer to errors of this sort as true word errors. Argument for grapheme-to-lexeme feedback. We interpret CM’s pattern of impaired spelling as evidence for feedback from grapheme to lexeme levels according to the following argument: (1) At least some of CM’s word errors are true word errors. (2) The true word errors show the letter persistence effect. (3) The occurrence of the persistence effect in the true word errors implies grapheme-to-lexeme feedback. Step 1: True word errors. Monte Carlo simulations established that CM’s word errors were too frequent to be accounted for in terms of word errors arising by chance at the grapheme level. At most, half of the observed word errors could be chance word errors. Step 2: Persistence effect for true word errors. Analyses of the persistence effect for true word errors established that the effect was too large to be attributed entirely to whatever chance word errors might be included among the word errors. Therefore, true word errors must have contributed to the effect. Step 3: Implications. A purely feedforward process (Lexeme ⇒ Grapheme) cannot account for the persistence effect in true word errors. In a true word error an incorrect lexeme is activated. What must be explained, therefore, is how incorrect lexemes for words (e.g., amber) that systematically share letters with preceding responses (e.g., bench) come to be activated. On a purely feedforward account lexemes are activated from semantic and perhaps phonological information. However, our analyses demonstrated that the persistence effect is a graphemic effect and not a semantic or phonological effect. That is, bench contributes to activation of amber by virtue of
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shared letters and not because of similar meanings or shared phonemes. To explain the persistence effect for true word errors, one must assume that letter representations (e.g., b and e for bench) persisting in an activated state at the grapheme level fed activation back to the lexeme level on subsequent trials, thereby contributing to activation of lexemes for words sharing the activated graphemes (e.g., AMBER). Therefore, CM’s error pattern implies feedback in addition to feedforward connections between grapheme and lexeme levels (Lexeme ⇔ Grapheme).
PLATFORM SESSION 3: READING AND WRITING Word-Centered Neglect Dyslexia and Aphasia in a Corrected Left-Hander
Gabriele Miceli and Rita Capasso Neurology, Catholic University, IRCCS S. Lucia, Rome, Italy
Introduction. Neuropsychological investigations of spatially specific reading disorders have led to the proposal that the early stages of word recognition involve three levels of representation. The retina-centered map represents the visual features of the stimulus in relation to their absolute position in the visual field, the stimulus-centered map represents specific letter shapes in relation to other letters in the stimulus, and the word-centered map consists of a graphemic description of the stimulus, in which abstract letter identities are ordered horizontally from left to right, centered with reference to the subject (Caramazza & Hillis, 1990). Subjects with damage to the wordcentered representation present with a well-defined neuropsychological profile: they read incorrectly letters in the contralesional half of the abstract representation, independent of stimulus orientation, case, and font, and make errors with comparable distribution in spelling. In addition, they also show neglect phenomena in purely visual tasks (e.g., line cancellation). The disorder is exceedingly rare, as only half a dozen cases are on record (see References). Consequently, both the theoretical implications and the anatomoclinical correlates of this deficit remain unclear. We report here on a new case of word-centered neglect dyslexia. Case history. SVE is a corrected left-hander with a 13th-grade education, who suffered from an ischemic right frontotemporoparietal lesion. He presents with anomia, ‘‘agrammatic’’ speech, and reduced verbal short-term memory; he also shows mild left neglect in line bisection and cancellation tasks. In reading aloud SVE, who reproduces correctly more words than pseudowords (70/92, 76.1% vs 10/45, 22.2%; χ 2 ⫽ 33.9; p ⬍ .001), makes errors almost exclusively (42/47, 89.4%) on stimulus-initial letters (grossa, big → ‘‘scossa,’’ quake; ravilo → ‘‘giovilo’’). Experimental study. Two-hundred forty 4-letter words were presented horizontally for 200 ms, in the left visual field, centered at the point of fixation, or in the right visual field (Fig. 16, upper half ). SVE read aloud correctly 389 0093-934X/99 $30.00
Copyright 1999 by Academic Press All rights of reproduction in any form reserved.
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FIG. 16. Reading aloud 4-letter words presented horizontally (upper half ) and vertically (lower left): occurrence of incorrectly reproduced letters in each position. The word CANE (dog) is presented as an example. Letters are shown as they appeared on the computer screen. 䊉, point of fixation, which always corresponded to the center of the computer screen. For horizontal presentation, words were located along the horizontal line passing at the center of the screen; for vertical presentation, two letters appeared above, and two below, the point of fixation.
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126/240 (52.5%), 144/240 (60%), and 155/240 (64.6%) words, respectively (χ 2 ⫽ 7.39; p ⬍ .05)—a result that suggests mild retinocentric damage. However, stimulus location was not the major determinant of performance in our subject, who systematically reproduced initial letters less accurately than final letters, independent of position in the visual field. For example, he made more errors on the first letter of words presented to the right of fixation (31.7% errors) than on the last letter of words presented to the left of fixation (4.6% errors), even though the former appeared in the ipsilesional hemifield and the latter in the contralesional hemifield (χ 2 ⫽ 57.5; p ⬍ .001). In addition, also irrespective of stimulus location, he performed with comparable accuracy on letters in the same within-word position. The same stimuli were presented vertically for 200 ms, to the left of the fixation point, at the fixation point, or to its right (Fig. 16, lower half ). SVE read aloud correctly 110/240 (45.8%), 150/240 (62.5%), and 151/240 (62.9%) words, respectively. Consistent with retinocentric neglect, he reproduced words presented to the left of fixation less accurately than words presented at the other two positions (p ⬍ .001). However, for each spatial location, SVE made more errors on the first than on any other letter ( p ⬍ .001 for all comparisons). Strikingly, this occurred even when words were presented vertically in the right (unaffected) visual field. Writing was severely impaired. Errors were often restricted to the initial letters of a target (pizza → . . . zza; barca, boat → circa, approximately). Overall, SVE managed to produce correctly 32/590.5 letters (5.4%) in the initial half and 265.5/590.5 letters (45%) in the final half of the response (χ 2 ⫽ 242.9; p ⬍ .001). SVE was presented for 200 ms with chimeric objects and asked to name the two halves of each chimera. He was comparably accurate when stimuli were presented in the left or in the right visual field, or at the center of the visual field (χ 2 ⫽ 1.63; p ⫽ n.s.), but systematically named the left half of a chimera less accurately than the right half (p ⬍ .001 for each location). This was true also for stimuli presented entirely in the right visual field. Discussion. The results produced by our subject can be easily summarized. Largely irrespective of stimulus orientation (horizontal, vertical) and absolute location in the visual field (left, center, right), SVE read aloud and wrote incorrectly word-initial letters and named incorrectly the left half of chimeric objects. This pattern of performance indicates damage to the word-centered representation. Thus, our subject adds to the extremely small number of cases in whom this disorder was documented. The observation of comparable performance on written words and chimeric objects suggests that this level of representation is shared by word and object recognition mechanisms. The relative contrast between marked neglect in tasks involving both visual and verbal processes, and the very mild disorder documented in purely visual tasks, presumably results from the interference of aphasia with wordcentered neglect.
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Retina-centered and stimulus-centered deficits are usually observed in right-handers after right-hemisphere damage (Hillis & Caramazza, 1995). In contrast, word-centered neglect has been reported both in left-handers and in dextrals, after damage to the right and to the left hemisphere (Barbut & Gazzaniga, 1987; Baxter & Warrington, 1983; Caramazza & Hillis, 1990; Hillis & Caramazza, 1995). SVE is a corrected left-hander with a righthemisphere lesion. Even though the anatomical basis of the word-centered representational level remains unclear, the observations reported in the various forms of neglect are consistent with the hypothesis that the levels of representation involved in visual word recognition are not only functionally, but also anatomically, distinct. REFERENCES Barbut, D., & Gazzaniga, M. 1987. Disturbances in conceptual space involving language and speech. Brain, 110, 1487–1496. Baxter, D. M., & Warrington, E. K. 1983. Neglect dysgraphia. Journal of Neurology, Neurosurgery and Psychiatry, 45, 1073–1078. Caramazza, A., & Hillis, A. E. 1990. Levels of representation, coordinate frames, and unilateral neglect. Cognitive Neuropsychology, 7, 391–445. Hillis, A. E., & Caramazza, A. 1995a. A framework for interpreting distinct patterns of hemispatial neglect. Neurocase, 1, 189–207. Hillis, A. E., & Caramazza, A. 1995b. Spatially specific deficits in processing graphemic representations in reading and writing. Brain and Language, 48, 263–308.
The Autonomy of Lexical Orthography: Evidence from Cortical Stimulation
Brenda Rapp,* Dana Boatman,† and Barry Gordon‡ *Cognitive Science Department, Johns Hopkins University; †Department of Neurology and Department of Otolaryngology, Johns Hopkins Medical School; and ‡Department of Neurology, Johns Hopkins Medical School, Baltimore, Maryland
Introduction In written language production, do we need to access the spoken form of a word in order to retrieve its spelling: meaning → lexical phonology → lexical orthography (obligatory phonological mediation)? Or, instead, is it possible to retrieve spelling directly from word meaning: meaning → lexical orthography (orthographic autonomy)? Clear evidence against the hypothesis of obligatory phonological mediation in written language production would be difficulty in retrieving the spoken forms of words for production in individuals who can, nonetheless, retrieve word spellings. A number of
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individuals with long-term deficits resulting from neurological injury have exhibited this pattern. Furthermore, in some of these studies it has been determined that the spoken naming deficits arose from difficulty in retrieving phonological lexical forms themselves rather than from damage to peripheral output mechanisms (Miceli et al., 1997; Rapp et al., 1997). Although this evidence favoring orthographic autonomy is extremely strong, one remaining concern is that direct links from word meaning to spelling are created only in situations in which individuals have suffered severe, long-term damage to spoken output processes. This investigation examines the possibility that the pattern of impaired spoken naming ⫹ preserved written naming might also be observed in the context of temporary, reversible deficits created through cortical electrical stimulation in individuals with normal language abilities. Such evidence would put to rest the concern that orthographic autonomy occurs only as an adaptation to chronic spoken language impairment. Case Studies Both of the subjects of this report suffered from chronic epilepsy and had subdural electrode arrays temporarily implanted for the purpose of localization of language functions and seizure foci prior to the surgical removal of the seizure foci. Case 1: LPN was a right-handed, 39-year-old female with 16 years of education. MRI revealed left mesial temporal sclerosis. WADA testing indicated left hemisphere dominance for language. LPN’s full scale (estimated) IQ was 117; she performed within normal limits on all language testing: naming (Boston), syntax, auditory comprehension (Token Test), oral word reading, and verbal fluency. Case 2: STS was a right-handed, 26-year-old male with 13 years of education. MRI results were normal. STS’s full scale (estimated) IQ was 103; he performed within normal limits on all language testing listed above. Methods Surgical procedures. Electrode arrays were surgically placed in the subdural space over the left hemisphere according to a preestablished protocol (Lesser et al., 1987). Arrays were composed of platinum disks, 3 mm in diameter, with a 2.3-mm-diameter exposed surface. Electrodes were 10 mm apart (center-to-center) in a rectangular pattern, embedded in medical-grade silastic. Electrical interference testing. Testing was initiated 2 days after surgical implantation of the electrode array. Cortical electrical interference was produced by 300-µs square-wave pulses of alternating polarity generated at a rate of 50 pulses per second through adjacent pairs of electrodes.
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Before testing each electrode site, the threshold current for afterdischarges or potential sensorimotor effects was established. If no afterdischarges or sensorimotor responses were present, the current was set to a maximal level of 15 mA. On stimulation trials, both stimulus and response were administered under electrical interference. The current remained activated for 5 s or until patients responded. Stimuli were presented approximately 1 s after current onset. The 5-s stimulus-response period was considered adequate in light of patients’ baseline response times without electrical interference. Cognitive testing. Patients were tested at each electrode pair on a range of tasks; we report on motor responses, spoken and written picture naming, and oral reading. The spoken and written picture naming tasks allow us to evaluate if subjects can proceed normally from picture recognition to meaning and then on to the retrieval of phonological and/or orthographic forms. Oral reading and motor responses allow us to evaluate the integrity of peripheral production mechanisms. Results Consistent with the hypothesis of orthographic autonomy, a pattern of impaired spoken picture naming accompanied by intact written picture naming was observed at multiple electrode sites for each subject. The observed deficits in spoken naming could not be attributed to interruption of the spoken production process at a peripheral level since tongue movements and oral reading were not affected. Furthermore, difficulty in spoken naming could not be attributed to a greater vulnerability of spoken naming mechanisms as STS exhibited the reverse dissociation of intact spoken naming and impaired written naming (Table 18).
TABLE 18 Percentage Correct across Various Tasks under Cortical Stimulation (T, Temporal Lobe; F, Frontal Lobe) Electrode site Subject LPN Posterior, midinferior T Posterior, midinferior T Posterior, basal T Subject STS Inferior, posterior F Inferior, anterior F Middle F Inferior, posterior F
Spoken naming
Written naming
Oral reading
Tongue, hand, finger mvmts
0% 25% 40%
100% 100% 100%
Mild slowing Mild slowing 100%
100% 100% 100%
20% 25% 100% 100%
100% 100% 20% 40%
100% 100% 100% 100%
100% 100% 100% 100%
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Conclusions The results of this study reveal that with electrical cortical stimulation techniques it is possible to interfere (at specific cortical locations) with the retrieval of lexical phonological forms without interfering with the retrieval of orthographic forms. These results allow us to conclude that the architecture of the naming system is organized so that orthographic lexical forms can be independently accessed for production without the mediating role of phonology. Furthermore, these results, obtained under conditions of temporary disruption of cortical activity, converge on conclusions reached from the study of subjects with long-term disruption. Thus, in addition to confirming the hypothesis of orthographic autonomy, these findings increase our confidence that the patterns of performance observed in subjects with long-term deficits may indeed legitimately form the basis for inferences about the functional organization of unimpaired cognitive systems. REFERENCES Lesser, R., Luders, H., Klem, G., et al. 1987. Extra-operative cortical functional localization in patients with epilepsy. Journal of Clinical Neuropsychology, 4, 27–53. Miceli, G., Benvegnu, B., Capasso, R., & Caramazza, A. 1997. The independence of phonological and orthographic lexical forms: Evidence from aphasia. Cognitive Neuropsychology, 14, 35–69. Rapp, B., Benzing, L., & Caramazza, A. 1997. The autonomy of lexical orthography. Cognitive Neuropsychology, 14, 71–104.
Grapheme-to-Lexeme Feedback in the Spelling System: Evidence from Dysgraphia
Michael McCloskey,* Paul Macaruso,† and Brenda Rapp* *Johns Hopkins University, Baltimore, Maryland; and †Community College of Rhode Island, Warwick, Rhode Island
Cognitive processes typically involve multiple levels of representation. For example, the process of writing a word may begin with a meaning to be expressed (e.g., domesticated animal that gives milk). From the semantic representation a lexical representation, or lexeme, may be activated (e.g., COW ). The lexeme representation may in turn activate abstract grapheme representations (C, O, W), which then activate letter-shape representations, and so on until the motor response is completed. A central issue concerns how the various levels of representation interact. For example, is the flow of information purely feedforward, as in (1), or is
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there multidirectional information flow, such that the various levels constrain one another via feedback as well as feedforward connections, as in (2)? Semantic ⇒ Lexeme ⇒ Grapheme
(1)
Semantic ⇔ Lexeme ⇔ Grapheme
(2)
This abstract focuses on interaction between lexeme and grapheme levels in writing. We present data from a brain-damaged patient as evidence for grapheme-to-lexeme feedback. Patient CM Patient CM is a 63-year-old man with a Ph.D. in electrical engineering. He worked as a researcher in a university laboratory until suffering a left middle cerebral artery CVA in 1986. CM’s language comprehension is mildly impaired (although single-word comprehension is intact), and both spoken and written language production are severely impaired. Experimental Study Over a 3-year period CM was presented with 3797 words in a writingto-dictation task. On each trial a word was dictated, CM repeated the word, then wrote the word, and then repeated it again. Although his repetition responses were uniformly correct, CM erred in spelling 1696 of the stimulus words (45%). Examples of his errors include half → halp, tip → tobe, and dignify → define. Two features of CM’s errors are relevant to our argument for grapheme-to-lexeme feedback: Letter intrusions and word errors. Letter intrusions. CM’s misspellings frequently included letters that did not appear in the correct spelling (e.g., the p in half → halp). The error corpus included 3354 of these intruded letters. As illustrated in the following trial sequence, many of the intruded letters were present in CM’s responses on one or more of the immediately preceding trials. For example, the intruded I in filter appears in three of the four prior responses (toples, wilten, bolt). Dictated stimulus casket blow wilt topple wept fit
CM’s written response casket bolt wilten toples wept filter
Analyses revealed that intruded letters appeared more often than expected by chance in responses on the five trials preceding the error. Additional analyses established that this letter persistence effect arose at a level of abstract grapheme representations and not at phonological or semantic levels or at
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more peripheral levels in the writing system (e.g., letter shape or graphomotor levels). The persistence effect may be interpreted by assuming that grapheme representations activated in spelling a word often remained active and consequently intruded on subsequent trials. Word errors. The second relevant feature of CM’s performance is that one-third of his errors (556/1696) took the form of words (e.g., dignify → define; arm → amber). Analyses revealed that like the error corpus as a whole, the word errors showed a strong letter persistence effect; that is, intruded letters in word responses were more likely than expected by chance to have appeared in preceding responses. For example, the intruded letters b and e in the arm → amber error occurred in the immediately preceding response (bench). Word errors could arise by chance at the grapheme level; that is, substitution or insertion of incorrect graphemes (e.g., insertion of a p after the s in sort) could produce a letter string that happened by chance to be a word (e.g., sport). We refer to such errors as chance word errors. However, word errors could also result from activation of the wrong word representation at the lexeme level (e.g., the lexeme AMBER when arm was dictated). We refer to errors of this sort as true word errors. Argument for grapheme-to-lexeme feedback. We interpret CM’s pattern of impaired spelling as evidence for feedback from grapheme to lexeme levels according to the following argument: (1) At least some of CM’s word errors are true word errors. (2) The true word errors show the letter persistence effect. (3) The occurrence of the persistence effect in the true word errors implies grapheme-to-lexeme feedback. Step 1: True word errors. Monte Carlo simulations established that CM’s word errors were too frequent to be accounted for in terms of word errors arising by chance at the grapheme level. At most, half of the observed word errors could be chance word errors. Step 2: Persistence effect for true word errors. Analyses of the persistence effect for true word errors established that the effect was too large to be attributed entirely to whatever chance word errors might be included among the word errors. Therefore, true word errors must have contributed to the effect. Step 3: Implications. A purely feedforward process (Lexeme ⇒ Grapheme) cannot account for the persistence effect in true word errors. In a true word error an incorrect lexeme is activated. What must be explained, therefore, is how incorrect lexemes for words (e.g., amber) that systematically share letters with preceding responses (e.g., bench) come to be activated. On a purely feedforward account lexemes are activated from semantic and perhaps phonological information. However, our analyses demonstrated that the persistence effect is a graphemic effect and not a semantic or phonological effect. That is, bench contributes to activation of amber by virtue of
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shared letters and not because of similar meanings or shared phonemes. To explain the persistence effect for true word errors, one must assume that letter representations (e.g., b and e for bench) persisting in an activated state at the grapheme level fed activation back to the lexeme level on subsequent trials, thereby contributing to activation of lexemes for words sharing the activated graphemes (e.g., AMBER). Therefore, CM’s error pattern implies feedback in addition to feedforward connections between grapheme and lexeme levels (Lexeme ⇔ Grapheme).