When writing 0 (zero) is easier than writing O (o): a neuropsychological case study of agraphia

Writing letters in two graphic systems: Behavioral and neural correlates in Latin-Arabic biscripters

Biscriptuality is the ability to read and write using two scripts. Despite the increasing number of biscripters, this phenomenon remains poorly understood. Here, we focused on investigating graphomotor processing in French-Arabic biscripters. We chose the French and Arabic alphabets because they have comparable visuospatial complexity and linguistic features, but differ dramatically in their graphomotor characteristics. In a first experiment we describe the graphomotor features of the two alphabets and showed that while Arabic and Latin letters are produced with the same velocity and fluency, Arabic letters require more pen lifts, contain more right-to-left strokes and clockwise curves, and take longer to write than Latin letters. These results suggest that Arabic and Latin letters are produced via different motor patterns. In a second experiment we used functional magnetic resonance imaging to ask whether writing the two scripts relies upon partially distinct or fully overlapping neural networks, and whether the elements of the previously described handwriting network are recruited to the same extent by the two scripts. We found that both scripts engaged the so-called "writing network", but that within the network, Arabic letters recruited the left superior parietal lobule (SPL) and the left primary motor cortex (M1) more strongly than Latin letters. Both regions have previously been identified as holding scale-invariant representations of letter trajectories. Arabic and Latin letters also activated distinct regions that do not belong to the writing network. Complementary analyses indicate that the differences observed between scripts at the neural level could be driven by the specific graphomotor features of each script. Overall, our results indicate that particular features of the practiced scripts can lead to different motor organization at both the behavioral and brain levels in biscripters.

Handwriting in Alzheimer's Disease

BACKGROUND

Agraphia is a typical feature in the clinical course of Alzheimer's disease (AD).

OBJECTIVE

Assess the differences between AD and normal aging as regards kinematographic features of handwriting and elucidate writing deficits in AD.

METHODS

The study included 23 patients with AD (78.09 years/SD = 7.12; MMSE 21.39/SD = 3.61) and 34 healthy controls (75.56 years/SD = 5.85; MMSE 29.06/SD = 0.78). Both groups performed alphabetical and non-alphabetical writing tasks. The kinematographic assessment included the average number of inversions per stroke (NIV; number of peaks in the velocity profile in a single up or down stroke), percentage of automated segments, frequency (average number of strokes per second), writing pressure, and writing velocity on paper.

RESULTS

A total of 14 patients showed overt writing difficulties reflected by omissions or substitutions of letters. AD patients showed less automated movements (as measured by NIV), lower writing velocity, and lower frequency of up-and-down strokes in non-alphabetical as well as in alphabetical writing. In the patient group, Spearman correlation analysis between overt writing performance and NIV was significant. That means patients who had less errors in writing a sentence showed a higher automaticity in handwriting. The correctness of alphabetical writing and some kinematographic measures in writing non-alphabetical material reached excellent diagnostic values in ROC analyses. There was no difference in the application of pressure on the pen between patients and controls.

CONCLUSION

Writing disorders are multi-componential in AD and not strictly limited to one processing level. The slow and poorly automated execution of motor programs is not bound to alphabetical material.

Word deafness with preserved number word perception

We describe the performance of an aphasic individual, K.A., who showed a selective impairment affecting his ability to perceive spoken language, while largely sparing his ability to perceive written language and to produce spoken language. His spoken perception impairment left him unable to distinguish words or nonwords that differed on a single phoneme and he was no better than chance at auditory lexical decision or single spoken word and single picture matching with phonological foils. Strikingly, despite this profound impairment, K.A. showed a selective sparing in his ability to perceive number words, which he was able to repeat and comprehend largely without error. This case adds to a growing literature demonstrating modality-specific dissociations between number word and non-number word processing. Because of the locus of K.A.'s speech perception deficit for non-number words, we argue that this distinction between number word and non-number word processing arises at a sublexical level of representations in speech perception, in a parallel fashion to what has previously been argued for in the organization of the sublexical level of representation for speech production.

Neuroanatomy of Handwriting and Related Reading and Writing Skills in Adults and Children with and without Learning Disabilities: French-American Connections

In this article, we present recent neuroimaging studies performed to identify the neural network involved in handwriting. These studies, carried out in adults and in children, suggest that the mastery of handwriting is based on the involvement of a network of brain structures whose involvement and inter-connection are specific to writing alphabet characters. This network is built upon the joint learning of writing and reading and depends on the level of expertise of the writer. In addition, a part of this graphomotor network is also brought into play during the identification letters during visual reading. These skills are also the basis for the development of more complex language activities involving orthographic knowledge and composition of texts. The studies presented cover two perspectives: that of neuroscience and that of cognitive psychology, as both are necessary to understand a complex process of writing and both depend on natural interactions and the influence of educational exposure.

What letters can "learn" from Arabic digits--fMRI-controlled single case therapy study of peripheral agraphia

Research on (hand-)writing has revealed that Exner's area subserves transferring linguistic impulses into writing programmes. We report on a patient with a lesion affecting Broca's and Exner's area suffering from severe peripheral agraphia for letters but not for Arabic digits. Analogous to semantic (magnitude) information in numbers, we developed a specifically tailored writing training: additional mental imagery based semantic information was attached to letters. The training resulted in significant improvements. Imaging data revealed stronger fronto-parietal network activity including perilesional activation around Exner's area and precuneus for writing letters to dictation than for writing letters corresponding to their mental image expressions. Follow-up testing showed not only stable training effects but also an activation shift into the left angular gyrus. Results document neuronal correlates of a successful intervention by attaching additional meanings to letters in order to retrieve their grapho-motor patterns. These findings contribute to understanding the impact of Exner's area.

Patterns of linguistic and numerical performance in aphasia

BACKGROUND

Empirical research on the relationship between linguistic and numerical processing revealed inconsistent results for different levels of cognitive processing (e.g., lexical, semantic) as well as different stimulus materials (e.g., Arabic digits, number words, letters, non-number words). Information of dissociation patterns in aphasic patients was used in order to investigate the dissociability of linguistic and numerical processes. The aim of the present prospective study was a comprehensive, specific, and systematic investigation of relationships between linguistic and numerical processing, considering the impact of asemantic vs. semantic processing and the type of material employed (numbers compared to letters vs. words).

METHODS

A sample of aphasic patients (n = 60) was assessed with a battery of linguistic and numerical tasks directly comparable for their cognitive processing levels (e.g., perceptual, morpho-lexical, semantic).

RESULTS AND CONCLUSIONS

Mean performance differences and frequencies of (complementary) dissociations in individual patients revealed the most prominent numerical advantage for asemantic tasks when comparing the processing of numbers vs. letters, whereas the least numerical advantage was found for semantic tasks when comparing the processing of numbers vs. words. Different patient subgroups showing differential dissociation patterns were further analysed and discussed. A comprehensive model of linguistic and numerical processing should take these findings into account.

Functional specificity in the motor system: Evidence from coupled fMRI and kinematic recordings during letter and digit writing

A few intriguing neuropsychologial studies report dissociations where agraphic patients are severely impaired for writing letters whereas they write digits nearly normally. Here, using functional magnetic resonance imaging (fMRI) together with graphic tablet recordings, we tested the hypothesis that the motor patterns for writing letters are coded in specific regions of the cortex. We found a set of three regions that were more strongly activated when participants wrote letters than when they wrote digits and whose response was not explained by low-level kinematic features of the graphic movements. Two of these regions (left dorsal premotor cortex and supplementary motor complex) are part of a motor control network. The left premotor activation belongs to what is considered in the literature a key area for handwriting. Another significant activation, likely related to phoneme-to-grapheme conversion, was found in the right anterior insula. This constitutes the first neuroimaging evidence of functional specificity derived from experience in the cortical motor system.

Double dissociations of word and number processing in auditory and written modalities: a case study

We report an individual with a massive left-hemisphere lesion, who showed reverse patterns of dissociations between word and number processing in two modalities (auditory comprehension and written production). His performance in auditory comprehension was perfect for words, but severely impaired for numbers. In written production, he performed significantly better at writing numbers (both Arabic numbers and word numbers) than writing words. His visual comprehension fell into normal range for words and numbers while his oral production was at floor for both. This case profile adds further evidence to the functional/neural segregation of word and number processing systems.

The specificity of notation codes in apraxic agraphia: dissociation between Arabic and alphabetical scripts in a patient with severe ideomotor and visuoconstructional apraxia

This article describes the case of a patient with corticobasal syndrome, who showed severe ideomotor and visuoconstructional apraxia along with handwriting difficulties more marked for letters and words than for digits and numbers. For alphabetical script, these difficulties were less marked when graphic motor patterns were activated with a model, whilst for digits IV's graphic productions were better in dictation. Moreover, IV's graphic production was negatively influenced by graphomotor complexity for letters but not for numbers. IV is the first reported case of a patient with severe limb apraxia, who also showed peripheral agraphia, with dissociation in alphabetical and numerical notation codes resulting from a specific deficit in the activation of graphomotor programs.

Dyscravia: voicing substitution dysgraphia

We report a new type of dysgraphia, which we term dyscravia. The main error type in dyscravia is substitution of the target letter with a letter that differs only with respect to the voicing feature, such as writing "coat" for "goat", and "vagd" for "fact". Two Hebrew-speaking individuals with acquired dyscravia are reported, TG, a man aged 31, and BG, a woman aged 66. Both had surface dysgraphia in addition to their dyscravia. To describe dyscravia in detail, and to explore the rate and types of errors made in spelling, we administered tests of writing to dictation, written naming, and oral spelling. In writing to dictation, TG made voicing errors on 38% of the words, and BG made 17% voicing errors. Voicing errors also occurred in nonword writing (43% for TG, 56% for BG). The writing performance and the variables that influenced the participants' spelling, as well as the results of the auditory discrimination and repetition tasks indicated that their dyscravia did not result from a deficit in auditory processing, the graphemic buffer, the phonological output lexicon, the phonological output buffer, or the allographic stage. The locus of the deficit is the phoneme-to-grapheme conversion, in a function specialized in the conversion of phonemes' voicing feature into graphemes. Because these participants had surface dysgraphia and were forced to write via the sublexical route, the deficit in voicing was evident in their writing of both words and nonwords. We further examined whether the participants also evinced parallel errors in reading. TG had a selective voicing deficit in writing, and did not show any voicing errors in reading, whereas BG had voicing errors also in the reading of nonwords (i.e., she had dyslegzia in addition to dyscravia). The dissociation TG demonstrated indicated that the voicing feature conversion is separate for reading and writing, and can be impaired selectively in writing. BG's dyslegzia indicates that the grapheme-to-phoneme conversion also includes a function that is sensitive to phonological features such as voicing. Thus the main conclusion of this study is that a separate function of voicing feature conversion exists in the phoneme-to-grapheme conversion route, which may be selectively impaired without deficits in other functions of the conversion route, and without a parallel deficit in reading.

Multisensory enhancement: gains in choice and in simple response times

Human observers can detect combinations of multisensory signals faster than each of the corresponding signals presented separately. In simple detection tasks, this facilitation in response times may reflect an enhancement in the perceptual processing stage or/and in the motor response stage. The current study compared the multisensory enhancements obtained in simple and choice response times (SRT and CRT, respectively) in bi- and tri-sensory (audio-visual-haptic) signal combinations using an identical experimental setup that differed only in the tasks--detecting the signals (SRT) or reporting the signals' location (CRT). Our measurements show that RTs were faster in the multisensory combinations conditions compared to the single stimulus conditions and that the absolute multisensory gains were larger in CRT than in SRT. These results can be interpreted in two ways. According to a serial stages model, the larger multisensory gains in CRT may suggest that when combinations of multisensory signals are presented, an additional enhancement occurs in the cognitive processing stages engaged in the CRT, beyond the enhancement in the perceptual and motor stages common to both SRT and CRT. Alternatively, the results suggest that multisensory enhancement reflect task-dependent interactions within and between multiple processing levels rather than facilitated processing modules. Thus, the larger absolute multisensory gains in CRT may reflect the inverse effectiveness principle, and Bayesian statistics, in that the maximal multisensory enhancements occur in the more difficult (less precise) uni-sensory conditions, i.e., in the CRT.

Deafness for the meanings of number words

We describe the performance of an aphasic individual who showed a selective impairment affecting his comprehension of auditorily presented number words and not other word categories. His difficulty in number word comprehension was restricted to the auditory modality, given that with visual stimuli (written words, Arabic numerals and pictures) his comprehension of number and non-number words was intact. While there have been previous reports of selective difficulty or sparing of number words at the semantic and post-semantic levels, this is the first reported case of a pre-semantic deficit that is specific to the category of number words. This constitutes evidence that lexical semantic distinctions are respected by modality-specific neural mechanisms responsible for providing access to the meanings of words.

Pure misallocation of “0” in number transcoding: A new symptom of right cerebral dysfunction

To account for the mechanism of number transcoding, many authors have proposed various models, for example, semantic-abstract model, lexical-semantic model, triple-code model, and so on. However, almost all of them are based on the symptoms of patients with left cerebral damage. Previously, I reported two Japanese patients with right posterior cerebral infarction showing pure misallocation of "0" (omission: "40,265"-->"4,265," addition: "107"-->"1,007," transposition: "4,072"-->"4,702") both in writing and oral reading of Arabic numerals. To examine whether the pure misallocation of "0" is commonly observed in patients with right cerebral damage, I investigated writing and oral reading of Arabic numerals in 18 patients with right cerebral damage and 16 healthy controls. All patients with right cerebral damage showed pure misallocation of "0" both in writing and reading. The pure misallocation of "0" due to right cerebral damage cannot be explained by current models. It may be more useful to explain the phenomenon by regarding an Arabic numeral as graph on a two-dimensional plane composed of two axes (place-holding values and digits).

Letter processing automatically recruits a sensory–motor brain network

Behavioral, neuropsychological and neuroimaging research suggest a distributed network that is recruited when we interact with letters. For the first time, we combine several letter processing tasks in a single experiment to study why letters seem to engage such disparate processing areas. Using fMRI, we investigate how the brain responds to letters using tasks that should recruit systems for letter perception, letter writing, letter copying and letter imagery. We describe a network of five cortical regions including the left fusiform gyrus, two left pre-central areas, left cuneus and the left inferior frontal gyrus that are all selectively engaged during a 1-back matching paradigm with letters. Our results suggest involvement of these regions to different extents in different tasks. However, the regions also form an integrated network such that letter perception also engages motor regions while writing recruits letter-specific visual regions as well. We suggest that this distributed network is a direct result of our sensory-motor interactions with letters.