White matter disconnectivity fingerprints causally linked to dissociated forms of alexia

For over 150 years, the study of patients with acquired alexia has fueled research aimed at disentangling the neural system critical for reading. An unreached goal, however, relates to the determination of the fiber pathways that root the different visual and linguistic processes needed for accurate word reading. In a unique series of neurosurgical patients with a tumor close to the visual word form area, we combine direct electrostimulation and population-based streamline tractography to map the disconnectivity fingerprints characterizing dissociated forms of alexia. Comprehensive analyses of disconnectivity matrices establish similarities and dissimilarities in the disconnection patterns associated with pure, phonological and lexical-semantic alexia. While disconnections of the inferior longitudinal and posterior arcuate fasciculi are common to all alexia subtypes, disconnections of the long arcuate and vertical occipital fasciculi are specific to phonological and pure alexia, respectively. These findings provide a strong anatomical background for cognitive and neurocomputational models of reading.

A computational model of typical and impaired reading: the role of visual processing

Computational modelling has served as a powerful tool to advance our understanding of language processes by making theoretical ideas rigorously specified and testable (a form of 'open science' for theory building). In reading research, one of the most influential computational modelling frameworks is the triangle model of reading that characterises the mappings between orthography, phonology and semantics. Currently, most instantiations of the triangle modelling framework start the processes from orthographic levels which abstract away visual processing. Moreover, without visual processing, most models do not provide an opportunity to investigate visual-related dyslexia. To bridge this crucial gap, the present study extended the existing triangle models by implementing an additional visual input. We trained the model to learn to read from visual input without pre-defined orthographic representations. The model was assessed by reading tasks in both intact and after damage (to mimic acquire alexias). The simulation results demonstrated that the model was able to name word and nonwords as well as make lexical decisions. Damage to the visual, phonological or semantic components of the model resulted in the expected reading impairments associated with pure alexia, phonological dyslexia, and surface dyslexia, respectively. The simulation results demonstrated for the first time that both typical and neurologically-impaired reading including both central and peripheral dyslexia could be addressed in this extended triangle model of reading. The findings are consistent with the primary systems account.

HOW PURE IS PURE ALEXIA? A NEUROPSYCHOLOGICAL ANALYSIS OF A CASE SERIES OF PATIENTS WITH ALEXIA DUE TO LEFT HEMISPHERIC STROKES

The aim of this study was to analyze a case series with acquired alexia after stroke within the posterior areas of the left hemisphere, in the context of the current criteria for pure alexia and their relevance to the set of symptoms observable in clinical practice. Seven patients with ischemic strokes and an initial diagnosis of pure alexia were enrolled for detailed analysis. The evaluation consisted of neuropsychological assessment in the form of standardized tests and non-standardized reading tasks, while oculomotor activity during reading was measured. Language functions, visual object and space perception, verbal and nonverbal memory, and visuospatial constructional ability were among the domains assessed. In five of the participants, pure alexia was recognized based on sig- nificant and specific discrepancies between test scores, indicating primary abnormalities in the visual processing of letter strings as a basic mechanism of the disorder. In most of the patients, coexisting cognitive deficits were revealed; however, these were dispropor- tionately milder and less functionally significant than reading disturbances. Pure alexia is a relatively rare disorder after a stroke, but it considerably affects the quality of everyday independent functioning. Its clinical characteristics in practice rarely meet all the criteria proposed in the subject literature. The differential diagnosis of this form of alexia and other reading disorders requires detailed clinical analysis.

Abstract WP493: Post-Stroke Chinese Pure Alexia: Prominent Shape-Similar Errors and Associated Neuropsychological Profiles

Objective: To describe the characteristics of post-stroke Chinese pure alexia and associated neuropsychological profiles. Methods: All patients with post-stroke pure alexia from the neurology department of our hospital were enrolled from June 2018 to July 2019. Brain MRI was performed to evaluate the stroke radiologically. The Aphasia Battery of Chinese (ABC) was used to evaluate the general language functions. A Chinese individual character reading test including 68 commonly used characters was used to evaluate the ability to read individual Chinese characters. The numbers of correct reading and misreading were recorded, and the error types of misreading were analyzed. MMSE, auditory verbal learning test, cube copying task, clock drawing test, and picture copying tests were performed to evaluate other cognitive impairments. Results: A total of 5 male patients were included, with a median age of 58 years (50-64 years). They all had Chinese pure alexia with intact verbal comprehension and speech and relatively preserved writing skills. The etiologies were all acute infarction involving the left temporo-parietal lobe and splenium of corpus callosum. In the Chinese individual character reading test, the median number of correct reading was 21 (18-44) out of 68 characters, with many shape-similar errors (one character was read as another one with a similar shape but different meaning and pronunciation). The percentage of shape-similar errors among all type errors was 81.5%, 60.0%, 23.7%, 18.5%, and 57.9% respectively, and 43.1% overall, much higher than other type errors. All the patients had obvious impairment in memory and visuospatial function with an exception that one patient had relatively preserved visuospatial ability. Conclusion: Shape-similar error is a remarkable feature of Chinese pure alexia. Chinese pure alexia is associated with impaired visuospatial function, but visuospatial dysfunction is not necessary for the development of Chinese pure alexia.

A Computational Model of Normal and Impaired Lexical Decision: Graded Semantic Effects

Lexical decision is an important paradigm in studies of visual word recognition yet the underlying mechanisms supporting the activity are not well understood. While most models of visual word recognition focus on orthographic processing as the primary locus of the lexical decision, a number of behavioural studies have suggested a flexible role for semantic processing regulated by the similarity of the nonword foil to real words. Here we developed a computational model that interactively combines visual-orthographic, phonological and semantic processing to perform lexical decisions. Importantly, the model was able to differentiate words from nonwords by dynamically integrating measures of polarity across the key processing layers. The model was more reliant on semantic information when nonword foils were pseudowords as opposed to consonant strings. Moreover, the model was able to capture a range of standard reading effects in lexical decision. Damage to the model also resulted in reading patterns observed in patients with pure alexia, phonological dyslexia, and semantic dementia, demonstrating for the first time that both normal and neurologically-impaired lexical decision can be addressed in a connectionist computational model of reading.