What's in a name? The characterization of pure alexia

Neuropsychological Diagnosis and Assessment of Alexia: A Mixed-Methods Study

The neuropsychological diagnosis and assessment of alexia remain formidable due to its multifaceted presentations and the intricate neural underpinnings involved. The current study employed a mixed-method design, incorporating cluster and thematic analyses, to illuminate the complexities of alexia assessment. We used the Web of Science and Scopus to retrieve articles spanning from 1985 to February 2024. Our selection was based on identified keywords in relation to the assessment and diagnosis of alexia. The analysis of 449 articles using CiteSpace (Version 6.3.R1) and VOSviewer (Version 1.6.19) software identified ten key clusters such as 'pure alexia' and 'posterior cortical atrophy', highlighting the breadth of research within this field. The thematic analysis of the most cited and recent studies led to eight essential categories. These categories were synthesized into a conceptual model that illustrates the interaction between neural, cognitive, and diagnostic aspects, in accordance with the International Classification of Functioning, Disability, and Health (ICFDH) framework. This model emphasizes the need for comprehensive diagnostic approaches extending beyond traditional reading assessments to include specific tasks like character identification, broader visual processing, and numerical tasks. Future diagnostic models should incorporate a diverse array of alexia types and support the creation of advanced assessment tools, ultimately improving clinical practice and research.

Cortical and Subcortical Mechanisms of Orthographic Word-form Learning

We examined the initial stages of orthographic learning in real time as literate adults learned spellings for spoken pseudowords during fMRI scanning. Participants were required to learn and store orthographic word forms because the pseudoword spellings were not uniquely predictable from sound to letter mappings. With eight learning trials per word form, we observed changes in the brain's response as learning was taking place. Accuracy was evaluated during learning, immediately after scanning, and 1 week later. We found evidence of two distinct learning systems-hippocampal and neocortical-operating during orthographic learning, consistent with the predictions of dual systems theories of learning/memory such as the complementary learning systems framework [McClelland, J. L., McNaughton, B. L., & O'Reilly, R. C. Why there are complementary learning systems in the hippocampus and neocortex: Insights from the successes and failures of connectionist models of learning and memory. Psychological Review, 102, 419-457, 1995]. The bilateral hippocampus and the visual word form area (VWFA) showed significant BOLD response changes over learning, with the former exhibiting a rising pattern and the latter exhibiting a falling pattern. Moreover, greater BOLD signal increase in the hippocampus was associated with better postscan recall. In addition, we identified two distinct bilateral brain networks that mirrored the rising and falling patterns of the hippocampus and VWFA. Functional connectivity analysis revealed that regions within each network were internally synchronized. These novel findings highlight, for the first time, the relevance of multiple learning systems in orthographic learning and provide a paradigm that can be used to address critical gaps in our understanding of the neural bases of orthographic learning in general and orthographic word-form learning specifically.

Post-stroke Chinese pure alexia: linguistic features and neuropsychological profiles

PURPOSE

Very few cases of Chinese pure alexia have been reported to date. We aim to summarize the linguistic features and neuropsychological profiles of Chinese pure alexia through a case series study.

METHODS

11 consecutive patients with post-stroke Chinese pure alexia and 11 healthy controls were included. The Aphasia Battery of Chinese (ABC) and 68-Chinese character oral reading test (68-character test) were used to evaluate the reading and writing ability. Reading errors were classified based on the performance of 68-character test. Neuropsychological profiles were evaluated with corresponding scales. The possible correlation between the reading ability and the writing ability or neuropsychological performance was analyzed.

RESULTS

The patients had a correct rate of 43.7 ± 23.2% in the 68-character test, significantly lower (P < 0.001) than that of controls. Shape-similar error was the most common type of reading error (101/209, 48.3%). The ABC total writing score rate of the patients ranged from 68.9% to 98.7% (median, 90.5%), significantly lower (P < 0.001) than that of the controls. The patients also showed worse performance in MMSE, auditory verbal learning test, Boston naming test, intersecting pentagons copying and clock-drawing test (all P < 0.05). In the patient group, the correct rate of 68-character test was significantly correlated with the ABC total writing score rate (P = 0.008), the score rate of Boston naming test (P = 0.017), and the clock-drawing test score (P = 0.010).

CONCLUSION

Shape-similar errors may be a characteristic of Chinese pure alexia. The correlation between visuospatial dysfunction and pure alexia might explain the frequent occurrence of shape-similar errors in Chinese pure alexia.

Systematic evaluation of high-level visual deficits and lesions in posterior cerebral artery stroke

Knowledge about the consequences of stroke on high-level vision comes primarily from single case studies of patients selected based on their behavioural profiles, typically patients with specific stroke syndromes like pure alexia or prosopagnosia. There are, however, no systematic, detailed, large-scale evaluations of the more typical clinical behavioural and lesion profiles of impairments in high-level vision after posterior cerebral artery stroke. We present behavioural and lesion data from the Back of the Brain project, to date the largest (N = 64) and most detailed examination of patients with cortical posterior cerebral artery strokes selected based on lesion location. The aim of the current study was to relate behavioural performance with faces, objects and written words to lesion data through two complementary analyses: (i) a multivariate multiple regression analysis to establish the relationships between lesion volume, lesion laterality and the presence of a bilateral lesion with performance and (ii) a voxel-based correlational methodology analysis to establish whether there are distinct or separate regions within the posterior cerebral artery territory that underpin the visual processing of words, faces and objects. Behaviourally, most patients showed more general deficits in high-level vision (n = 22) or no deficits at all (n = 21). Category-selective deficits were rare (n = 6) and were only found for words. Overall, total lesion volume was most strongly related to performance across all three domains. While behavioural impairments in all domains were observed following unilateral left and right as well as bilateral lesions, the regions most strongly related to performance mainly confirmed the pattern reported in more selective cases. For words, these included a left hemisphere cluster extending from the occipital pole along the fusiform and lingual gyri; for objects, bilateral clusters which overlapped with the word cluster in the left occipital lobe. Face performance mainly correlated with a right hemisphere cluster within the white matter, partly overlapping with the object cluster. While the findings provide partial support for the relative laterality of posterior brain regions supporting reading and face processing, the results also suggest that both hemispheres are involved in the visual processing of faces, words and objects.

Contrasting domain-general and domain-specific accounts in cognitive neuropsychology: An outline of a new approach with developmental prosopagnosia as a case

The backbone of cognitive neuropsychology is the observation of (double) dissociations in performance between patients, suggesting some degree of independence between cognitive processes (domain specificity). In comparison, observations of associations between disorders/deficits have been deemed less evidential in neuropsychological theorizing about cognitive architecture. The reason is that associations can reflect damage to independent cognitive processes that happen to be mediated by structures commonly affected by the same brain disorder rather than damage to a shared (domain-general) mechanism. Here we demonstrate that it is in principle possible to discriminate between these alternatives by means of a procedure involving large unbiased samples. We exemplify the procedure in the context of developmental prosopagnosia (DP), but the procedure is in principle applicable to all neuropsychological deficits/disorders. A simulation of the procedure on a dataset yields estimates of dissociations/associations that are well in line with existing DP-studies, and also suggests that seemingly selective disorders can reflect damage to both domain-general and domain-specific cognitive processes. However, the simulation also highlights some limitations that should be considered if the procedure is to be applied prospectively. The main advantage of the procedure is that allows for examination of both associations and dissociations in the same sample. Hence, it may help even the balance in the use of associations and dissociations as grounds for neuropsychological theorizing.

Stroke disconnectome decodes reading networks

Cognitive functional neuroimaging has been around for over 30 years and has shed light on the brain areas relevant for reading. However, new methodological developments enable mapping the interaction between functional imaging and the underlying white matter networks. In this study, we used such a novel method, called the disconnectome, to decode the reading circuitry in the brain. We used the resulting disconnection patterns to predict a typical lesion that would lead to reading deficits after brain damage. Our results suggest that white matter connections critical for reading include fronto-parietal U-shaped fibres and the vertical occipital fasciculus (VOF). The lesion most predictive of a reading deficit would impinge on the left temporal, occipital, and inferior parietal gyri. This novel framework can systematically be applied to bridge the gap between the neuropathology of language and cognitive neuroscience.

Eye Signs in Stroke

A large part of the central nervous system is involved in the normal functioning of the vision, and hence vision can be affected in a stroke patient. Transient visual symptoms can likewise be a harbinger of stroke and prompt rapid evaluation for the prevention of recurrent stroke. A carotid artery disease can manifest as transient monocular visual loss (TMVL), central retinal artery occlusion (CRAO), anterior ischemic optic neuropathy or ocular ischemic syndrome (OIS). Stroke posterior to the optic chiasm can cause sectoranopias, quadrantanopias, or hemianopias, which can be either congruous or incongruous. Any stroke involving the dorsal stream (occipito-parietal lobe), or ventral stream (occipito-temporal lobe) can manifest with visuospatial perception deficits. Similarly, different ocular motility abnormalities can result from a stroke affecting the cerebrum, cerebellum, or brainstem. Among these deficits, vision and perception disorders are more difficult to overcome. Clinical, experimental, and neuroimaging studies have helped us to understand the anatomical basis, physiological dysfunction, and the underlying mechanisms of these neuro-ophthalmic signs.

Shallow or deep? The impact of orthographic depth on visual processing impairments in developmental dyslexia

The extent to which impaired visual and phonological mechanisms may contribute to the manifestation of developmental dyslexia across orthographies of varying depth has yet to be fully established. By adopting a cross-linguistic approach, the current study aimed to explore the nature of visual and phonological processing in developmental dyslexic readers of shallow (Italian) and deep (English) orthographies, and specifically the characterisation of visual processing deficits in relation to orthographic depth. To achieve this aim, we administered a battery of non-reading visual and phonological tasks. Developmental dyslexics performed worse than typically developing readers on all visual and phonological tasks. Critically, readers of the shallow orthography were disproportionately impaired on visual processing tasks. Our results suggest that the impaired reading and associated deficits observed in developmental dyslexia are anchored by dual impairments to visual and phonological mechanisms that underpin reading, with the magnitude of the visual deficit varying according to orthographic depth.

Holistic processing of faces and words predicts reading accuracy and speed in dyslexic readers

We compared the performance of dyslexic and typical readers on two perceptual tasks, the Vanderbilt Holistic Face Processing Task and the Holistic Word Processing Task. Both yield a metric of holistic processing that captures the extent to which participants automatically attend to information that is spatially nearby but irrelevant to the task at hand. Our results show, for the first time, that holistic processing of faces is comparable in dyslexic and typical readers but that dyslexic readers show greater holistic processing of words. Remarkably, we show that these metrics predict the performance of dyslexic readers on a standardized reading task, with more holistic processing in both tasks associated with higher accuracy and speed. In contrast, a more holistic style on the words task predicts less accurate reading of both words and pseudowords for typical readers. We discuss how these findings may guide our conceptualization of the visual deficit in dyslexia.

Category-selective deficits are the exception and not the rule: Evidence from a case-series of 64 patients with ventral occipito-temporal cortex damage

The organisational principles of the visual ventral stream are still highly debated, particularly the relative association/dissociation between word and face recognition and the degree of lateralisation of the underlying processes. Reports of dissociations between word and face recognition stem from single case-studies of category selective impairments, and neuroimaging investigations of healthy participants. Despite the historical reliance on single case-studies, more recent group studies have highlighted a greater commonality between word and face recognition. Studying individual patients with rare selective deficits misses (a) important variability between patients, (b) systematic associations between task performance, and (c) patients with mild, severe and/or non-selective impairments; meaning that the full spectrum of deficits is unknown. The Back of the Brain project assessed the range and specificity of visual perceptual impairment in 64 patients with posterior cerebral artery stroke recruited based on lesion localization and not behavioural performance. Word, object, and face processing were measured with comparable tests across different levels of processing to investigate associations and dissociations across domains. We present two complementary analyses of the extensive behavioural battery: (1) a data-driven analysis of the whole patient group, and (2) a single-subject case-series analysis testing for deficits and dissociations in each individual patient. In both analyses, the general organisational principle was of associations between words, objects, and faces even following unilateral lesions. The majority of patients either showed deficits across all domains or in no domain, suggesting a spectrum of visuo-perceptual deficits post stroke. Dissociations were observed, but they were the exception and not the rule: Category-selective impairments were found in only a minority of patients, all of whom showed disproportionate deficits for words. Interestingly, such selective word impairments were found following both left and right hemisphere lesions. This large-scale investigation of posterior cerebral artery stroke patients highlights the bilateral representation of visual perceptual function.

Reading and alexia

Alexia refers to a reading disorder caused by some form of acquired brain pathology, most commonly a stroke or tumor, in a previously literate subject. In neuropsychology, a distinction is made between central alexia (commonly seen in aphasia) and peripheral alexia (a perceptual or attentional deficit). The prototypical peripheral alexia is alexia without agraphia (pure alexia), where patients can write but are impaired in reading words and letters. Pure alexia is associated with damage to the left ventral occipitotemporal cortex (vOT) or its connections. Hemianopic alexia is associated with less extensive occipital damage and is caused by a visual field defect, which creates problems reading longer words and passages of text. Reading impairment can also arise due to attentional deficits, most commonly following right hemisphere or bilateral lesions. Studying patients with alexia, along with functional imaging studies of normal readers, has improved our understanding of the neurobiological processes involved in reading. A key question is whether an area in the left ventral occipitotemporal cortex is specialized for or selectively involved in word processing, or whether reading relies on tuning of more general purpose perceptual areas. Reading deficits may also be observed in dementia and traumatic brain injury, but often with less consistent deficit patterns than in patients with focal lesions.

Pure alexia with intact perception of complex visual stimuli: a case study

After a stroke involving the left occipitotemporal cortex our patient shows a word-length effect and has problems to identify letters or numbers in strings of symbols. But he is normal in identifying isolated letters and in non-verbally categorizing even complex images such as faces or natural scenes. His cortical lesion is stretching from the visual word form area (VWFA) anteriorly causing additional problems to name visual stimuli and to match acoustic stimuli with images. We conclude that our patient suffers from pure alexia without deficits to identify even complex visual stimuli. Our results directly contradict several explanations for letter-by-letter reading.

Are children with developmental dyslexia all the same? A cluster analysis with more than 300 cases

Reading is vital to every aspect of modern life, exacerbated by reliance of the internet, email, and social media on the written medium. Developmental dyslexia (DD) characterizes a disorder in which the core deficit involves reading. Traditionally, DD is thought to be associated with a phonological impairment. However, recent evidence has begun to suggest that the reading impairment in some individuals is provoked by a visual processing deficit. In this paper, we present WISC-IV data from more than 300 Italian children with a diagnosis of DD to investigate the manifestation of phonological and visual subtypes. Our results indicate the existence of two clusters of children with DD. In one cluster, the deficit was more pronounced in the phonological component, while both clusters were impaired in visual processing. These data indicate that DD may be an umbrella term that encompasses different profiles. From a theoretical perspective, our results demonstrate that dyslexia cannot be explained in terms of an isolated phonological deficit alone; visual impairment plays a crucial role. Moreover, general rather than specific accounts of DD are discussed.

Laterality for recognizing written words and faces in the fusiform gyrus covaries with language dominance

Recognizing words and faces engages highly specialized sites within the middle fusiform gyrus, known as the visual word form area (VWFA) and fusiform face area (FFA) respectively. The VWFA and FFA have clear but opposite population-level asymmetries, with the VWFA typically being lateralized to the left and the FFA to the right hemisphere. The present study investigates how language dominance may relate to these asymmetries. We hypothesize that individuals with left hemisphere dominance for word production (i.e., left language dominance, LLD) will have typical lateralization for word and face recognition in the fusiform gyrus, whereas participants with right language dominance (RLD) will demonstrate 'atypical' rightward laterality for words and leftward dominance for faces. To test this hypothesis, we recruited twenty-seven left-handers who had previously been identified as being LLD or RLD based on a visual half field task. Using fMRI, hemisphere dominance was determined for language (Broca's region) as well as for word and face recognition in the middle fusiform gyrus for each participant. The direction of asymmetry correlated significantly between language and recognizing words (ρ = .648, p < .001) as well as between language and face recognition (ρ = -.620, p = .001). Moreover, most LLD-participants were typically lateralized for faces and written words, while both functions tended to be reversed in individuals with RLD. However, segregation between language and face recognition was less clear in participants with RLD, as many of them lacked an obvious asymmetry for faces. Although our results thus suggest there is no one-on-one relationship between asymmetries for language, written word and face recognition, they also argue against a complete independence of their lateralization.

Orthographic connectivity in Arabic reading: a case study of an individual with deep dyslexia and letter-by-letter reading

Arabic orthography is complex, partly as a consequence of variations in orthographic connectivity. In this article, we present the case study of CHS, an Arabic individual with deep dyslexia associated with letter-by-letter reading. In the experimental study, we specifically explored the influence of orthographic connectivity on CHS's word recognition and reading abilities. Our results show that CHS's performance was better preserved for words and non-words made up of connected letters than made up of non-connected letters. CHS demonstrated impairment of visuoperceptual mechanisms, which affected the processing of complex orthographic material. These results provide insight into the cognitive processes associated with reading Arabic.

Voxel-based lesion analysis of brain regions underlying reading and writing

The neural basis of reading and writing has been a source of inquiry as well as controversy in the neuroscience literature. Reading has been associated with both left posterior ventral temporal zones (termed the "visual word form area") as well as more dorsal zones, primarily in left parietal cortex. Writing has also been associated with left parietal cortex, as well as left sensorimotor cortex and prefrontal regions. Typically, the neural basis of reading and writing are examined in separate studies and/or rely on single case studies exhibiting specific deficits. Functional neuroimaging studies of reading and writing typically identify a large number of activated regions but do not necessarily identify the core, critical hubs. Last, due to constraints on the functional imaging environment, many previous studies have been limited to measuring the brain activity associated with single-word reading and writing, rather than sentence-level processing. In the current study, the brain correlates of reading and writing at both the single- and sentence-level were studied in a large sample of 111 individuals with a history of chronic stroke using voxel-based lesion symptom mapping (VLSM). VLSM provides a whole-brain, voxel-by-voxel statistical analysis of the role of distinct regions in a particular behavior by comparing performance of individuals with and without a lesion at every voxel. Rather than comparing individual cases or small groups with particular behavioral dissociations in reading and writing, VLSM allowed us to analyze data from a large, well-characterized sample of stroke patients exhibiting a wide range of reading and writing impairments. The VLSM analyses revealed that reading was associated with a critical left inferior temporo-occipital focus, while writing was primarily associated with the left supramarginal gyrus. Separate VLSM analyses of single-word versus sentence-level reading showed that sentence-level reading was uniquely associated with anterior to mid-portions of the middle and superior temporal gyri. Both single-word and sentence-level writing overlapped to a great extent in the left supramarginal gyrus, but sentence-level writing was associated with additional underlying white matter pathways such as the internal capsule. These findings suggest that critical aspects of reading and writing processes diverge, with reading relying critically on the ventral visual recognition stream and writing relying on a dorsal visuo-spatial-motor stream.

Face and Word Recognition Can Be Selectively Affected by Brain Injury or Developmental Disorders

Face and word recognition have traditionally been thought to rely on highly specialised and relatively independent cognitive processes. Some of the strongest evidence for this has come from patients with seemingly category-specific visual perceptual deficits such as pure prosopagnosia, a selective face recognition deficit, and pure alexia, a selective word recognition deficit. Together, the patterns of impaired reading with preserved face recognition and impaired face recognition with preserved reading constitute a double dissociation. The existence of these selective deficits has been questioned over the past decade. It has been suggested that studies describing patients with these pure deficits have failed to measure the supposedly preserved functions using sensitive enough measures, and that if tested using sensitive measurements, all patients with deficits in one visual category would also have deficits in the other. The implications of this would be immense, with most textbooks in cognitive neuropsychology requiring drastic revisions. In order to evaluate the evidence for dissociations, we review studies that specifically investigate whether face or word recognition can be selectively affected by acquired brain injury or developmental disorders. We only include studies published since 2004, as comprehensive reviews of earlier studies are available. Most of the studies assess the supposedly preserved functions using sensitive measurements. We found convincing evidence that reading can be preserved in acquired and developmental prosopagnosia and also evidence (though weaker) that face recognition can be preserved in acquired or developmental dyslexia, suggesting that face and word recognition are at least in part supported by independent processes.

Reading on the right when there's nothing left? Probabilistic tractography reveals hemispheric asymmetry in pure alexia

We present a patient with reading inexpertise and right hemianopia following left posterior cerebral artery (PCA) stroke. We examine the extent of disruption to reading performance and the extent of white matter tract damage relative to a patient with more limited PCA infarction and isolated right hemianopia. We show white matter disconnection of the temporal occipital fusiform cortex in our pure alexia patient. Connectivity-based laterality indices revealed right hemisphere laterality in the alexia patient; this was not associated with improved reading function. We speculate that the degree of premorbid laterality may be a critical factor affecting the extent of reading dysfunction in alexia.

Word and text processing in developmental prosopagnosia

The "many-to-many" hypothesis proposes that visual object processing is supported by distributed circuits that overlap for different object categories. For faces and words the hypothesis posits that both posterior fusiform regions contribute to both face and visual word perception and predicts that unilateral lesions impairing one will affect the other. However, studies testing this hypothesis have produced mixed results. We evaluated visual word processing in subjects with developmental prosopagnosia, a condition linked to right posterior fusiform abnormalities. Ten developmental prosopagnosic subjects performed a word-length effect task and a task evaluating the recognition of word content across variations in text style, and the recognition of style across variations in word content. All subjects had normal word-length effects. One had prolonged sorting time for word recognition in handwritten stimuli. These results suggest that the deficit in developmental prosopagnosia is unlikely to affect visual word processing, contrary to predictions of the many-to-many hypothesis.

Treatment response profiles: An extension of the double dissociation concept in neuropsychological research

The presence of double dissociations in patients with neurological damage has long been used as evidence that the dissociated functions cannot be explained in terms of a common system or module. Shallice (1988) has suggested that a second procedure, the double critical variable method, can provide evidence for a similar conclusion. In this paper we examine the situation where double dissocations are not naturally present, suggesting that the two phenomena are merely aspects of the same underlying condition. We propose that the logic of the double critical variable method can be applied in this situation, whenever responses to treatment vary in a particular manner across syndromes and patients. This logic was previously used by Beschin, Cocchini, Allen, and Della Sala (2012) to show a dissociation between anosognosia and neglect in stroke patients; we suggest that it might have a more general application. As an aid in understanding the concept we also introduce the performance/performance curve; this builds on the existing idea of performance/resource curves to draw a single graph from two such curves, whose points may be derived from direct observation. It enables the empirical testing of hypotheses about the functional form of unobservable performance/resource relationships, and may be of use beyond the existing application to treatment response profiles.

Brain mechanisms of recovery from pure alexia: A single case study with multiple longitudinal scans

Pure alexia is an acquired reading disorder, typically due to a left occipito-temporal lesion affecting the Visual Word Form Area (VWFA). It is unclear whether the VWFA acts as a unique bottleneck for reading, or whether alternative routes are available for recovery. Here, we address this issue through the single-case longitudinal study of a neuroscientist who experienced pure alexia and participated in 17 behavioral, 9 anatomical, and 9 fMRI assessment sessions over a period of two years. The origin of the impairment was assigned to a small left fusiform lesion, accompanied by a loss of VWFA responsivity and by the degeneracy of the associated white matter pathways. fMRI experiments allowed us to image longitudinally the visual perception of words, as compared to other classes of stimuli, as well as the mechanisms of letter-by-letter reading. The progressive improvement of reading was not associated with the re-emergence of a new area selective to words, but with increasing responses in spared occipital cortex posterior to the lesion and in contralateral right occipital cortex. Those regions showed a non-specific increase of activations over time and an increase in functional correlation with distant language areas. Those results confirm the existence of an alternative occipital route for reading, bypassing the VWFA, but they also point to its key limitation: the patient remained a slow letter-by-letter reader, thus supporting the critical importance of the VWFA for the efficient parallel recognition of written words.

Word and text processing in acquired prosopagnosia

OBJECTIVE

A novel hypothesis of object recognition asserts that multiple regions are engaged in processing an object type, and that cerebral regions participate in processing multiple types of objects. In particular, for high-level expert processing, it proposes shared rather than dedicated resources for word and face perception, and predicts that prosopagnosic subjects would have minor deficits in visual word processing, and alexic subjects would have subtle impairments in face perception. In this study, we evaluated whether prosopagnosic subjects had deficits in processing either the word content or the style of visual text.

METHODS

Eleven prosopagnosic subjects, 6 with unilateral right lesions and 5 with bilateral lesions, participated. In the first study, we evaluated their word length effect in reading single words. In the second study, we assessed their time and accuracy for sorting text by word content independent of style, and for sorting text by handwriting or font style independent of word content.

RESULTS

Only subjects with bilateral lesions showed mildly elevated word length effects. Subjects were not slowed in sorting text by word content, but were nearly uniformly impaired in accuracy for sorting text by style.

INTERPRETATION

Our results show that prosopagnosic subjects are impaired not only in face recognition but also in perceiving stylistic aspects of text. This supports a modified version of the many-to-many hypothesis that incorporates hemispheric specialization for processing different aspects of visual text.

Clinical TVA-based studies: a general review

In combination with whole report and partial report tasks, the theory of visual attention (TVA) can be used to estimate individual differences in five basic attentional parameters: the visual processing speed, the storage capacity of visual short-term memory, the perceptual threshold, the efficiency of top-down selectivity, and the spatial bias of attentional weighting. TVA-based assessment has been used in about 30 studies to investigate attentional deficits in a range of neurological and psychiatric conditions: (a) neglect and simultanagnosia, (b) reading disturbances, (c) aging and neurodegenerative diseases, and most recently (d) neurodevelopmental disorders. The article introduces TVA based assessment, discusses its methodology and psychometric properties, and reviews the progress made in each of the four research fields. The empirical results demonstrate the general usefulness of TVA-based assessment for many types of clinical neuropsychological research. The method's most important qualities are cognitive specificity and theoretical grounding, but it is also characterized by good reliability and sensitivity to minor deficits. The review concludes by pointing to promising new areas for clinical TVA-based research.