Letter-by-letter reading: psychological descriptions of a neurological syndrome

Simultaneous simulations of pure, surface and phonological acquired dyslexia within a full computational model of the primary systems hypothesis

According to the primary systems hypothesis, reading requires interactions of visual-orthographic, phonological and semantic systems. Damage to each primary system generates very different types of acquired dyslexia. Variants of the connectionist 'triangle' models of reading have been developed to investigate individual acquired dyslexia. However, only a few studies have investigated multiple acquired alexia within one framework. Importantly, there are no studies that simultaneously simulate both central dyslexia (e.g. surface and phonological dyslexia) and peripheral dyslexia (e.g. pure alexia). That is largely due to the lack of a visual component in the traditional reading models. To verify the predictions made by the primary systems hypothesis, we developed a connectionist 'deep' multi-layer triangle model of reading including visual, orthographic, phonological and semantic processing layers. We investigated whether damage to the model could produce the general behavioural patterns of impaired performance observed in patients with the corresponding reading deficits. Crucially, damage to the visual-orthographic, 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 neurologically-impaired reading including both central and peripheral dyslexia could be addressed within a single triangle model of reading. The findings are consistent with the predictions made by the primary systems hypothesis.

Developmental surface dyslexia and dysgraphia in a child with corpus callosum agenesis: an approach to diagnosis and treatment

We present a case study detailing cognitive performance, functional neuroimaging, and effects of a hypothesis-driven treatment in a 10-year-old girl diagnosed with complete, isolated corpus callosum agenesis. Despite having average overall intellectual abilities, the girl exhibited profound surface dyslexia and dysgraphia. Spelling treatment significantly and persistently improved her spelling of trained irregular words, and this improvement generalized to reading accuracy and speed of trained words. Diffusion weighted imaging revealed strengthened intrahemispheric white matter connectivity of the left temporal cortex after treatment and identified interhemispheric connectivity between the occipital lobes, likely facilitated by a pathway crossing the midline via the posterior commissure. This case underlines the corpus callosum's critical role in lexical reading and writing. It demonstrates that spelling treatment may enhance interhemispheric connectivity in corpus callosum agenesis through alternative pathways, boosting the development of a more efficient functional organization of the visual word form area within the left temporo-occipital cortex.

Whole-object effects in visual word processing: Parallels with and differences from face recognition

Visual words and faces differ in their structural properties, but both are objects of high expertise. Holistic processing is said to characterize expert face recognition, but the extent to which whole-word processes contribute to word recognition is unclear, particularly as word recognition is thought to proceed by a component-based process. We review the evidence for experimental effects in word recognition that parallel those used to support holistic face processing, namely inversion effects, the part-whole task, and composite effects, as well as the status of whole-word processing in pure alexia and developmental dyslexia, contrasts between familiar and unfamiliar languages, and the differences between handwriting and typeset font. The observations support some parallels in whole-object influences between face and visual word recognition, but do not necessarily imply similar expert mechanisms. It remains to be determined whether and how the relative balance between part-based and whole-object processing differs for visual words and faces.

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.

Aphasia and acquired reading impairments: What are the high-tech alternatives to compensate for reading deficits?

BACKGROUND

People with aphasia (PWA) frequently present impairments in reading comprehension. Such impairments can be particularly debilitating due to the limitations and constraints they impose on everyday life. Recent technological advancements in the field of information and communication technologies offer many compensative tools for PWA. However, most technological tools are designed for patients with speech production impairments. Instruments addressing reading impairments associated with aphasia remain scarce and underrepresented in the scientific literature.

AIMS

To conduct a state-of-the-art review of the technologies currently available to PWA and acquired reading impairments. In particular, this review covers (1) research on technologies explicitly developed to compensate for reading difficulties associated with aphasia; and (2) research into which accessibility features included in mainstream high-tech systems are helpful for PWA when trying to access written material.

METHODS & PROCEDURES

Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) international standard, the authors conducted a systematic review from 2009 to 2019. The databases inspected were Scopus, Web of Science, PubMed, the Cochrane collection, IEEE Xplore, ScienceDirect and SpringerLink. Other research papers were included after checking the references of the selected papers.

MAIN CONTRIBUTION

The review reveals that research on compensative devices for reading impairments largely neglects tools for individuals with aphasia and acquired reading difficulties. Most of the studies in this field are qualitative investigations of how patients with literacy difficulties tackle everyday tasks with the help of mainstream technology (e.g., smartphone applications). Therefore, this paper highlights the scarce high-tech alternatives that support text comprehension in PWA and acquired reading impairments, and suggests further work on the development of customized software for smartphones and personal computers.

CONCLUSIONS

High-tech reading tools may help PWA to regain reading autonomy. PWA and acquired reading impairments employ a wide array of devices to overcome reading difficulties, which underlines the importance of reading in everyday life. However, the supports currently available are not yet flexible and accurate enough to answer their day-to-day needs. Thus, further work is necessary to enhance the compensative devices available to them. For instance, existing new technologies in the area of natural language processing (such as automatic text simplification) could potentially be used in compensative devices. What this paper adds What is already known on the subject Most research on high-tech compensative reading tools is focused on investigating how patients with aphasia and acquired reading impairments cope with their reading difficulties in everyday life by resorting to different types of technology. Yet, we still lack specific research on compensative reading technology for PWA. What this paper adds to existing knowledge This review shows that PWA with acquired reading impairments are offered limited options for accessing written content easily and autonomously-and those few resources that are available are not specifically designed for PWA. What are the potential or actual clinical implications of this work? Both aphasia and acquired reading impairments can vary in terms of both their severity and the associated typology of cognitive impairments. Therefore, it might be interesting to investigate flexible and highly adaptable reading support designed for them-and innovations in the field of information and communication technology might prove particularly fruitful.

Technology-Enhanced Reading Therapy for People With Aphasia: Findings From a Quasirandomized Waitlist Controlled Study

Purpose This study investigated the effects of technology-enhanced reading therapy for people with reading impairments, using mainstream assistive reading technologies alongside reading strategies. Method The study used a quasirandomized waitlist controlled design. Twenty-one people with reading impairments following stroke were randomly assigned to receive 14 hr of therapy immediately or after a 6-week delay. During therapy, participants were trained to use assistive reading technology that offered a range of features to support reading comprehension. They developed skills in using the technology independently and in applying the technology to their personal reading goals. The primary outcome measure assessed reading comprehension, using Gray Oral Reading Test-Fourth Edition (GORT-4). Secondary measures were as follows: Reading Comprehension Battery for Aphasia-Second Edition, Reading Confidence and Emotions Questionnaire, Communication Activities of Daily Living-Second Edition, Visual Analog Mood Scales, and Assessment of Living With Aphasia. Matched texts were used with the GORT-4 to compare technology-assisted and unassisted reading comprehension. Mixed analyses of variance explored change between T1 and T2, when the immediate group had received therapy but the delayed group had not, thus serving as untreated controls. Pretherapy, posttherapy, and follow-up scores on the measures were also examined for all participants. Results GORT-4 results indicated that the immediately treated group improved significantly in technology-assisted reading following therapy, but not in unassisted reading. However, the data were not normally distributed, and secondary nonparametric analysis was not significant. The control group was unstable over the baseline, improving significantly in unassisted reading. The whole-group analysis showed significant gains in assisted (but not unassisted) reading after therapy that were maintained at follow-up. The Reading Confidence and Emotions Questionnaire results improved significantly following therapy, with good maintenance of change. Results on all other secondary measures were not significant. Conclusions Technology-assisted reading comprehension improved following the intervention, with treatment compensating for, rather than remediating, the reading impairment. Participants' confidence and emotions associated with reading also improved. Gains were achieved after 14 therapy sessions, using assistive technologies that are widely available and relatively affordable, meaning that this approach could be implemented in clinical practice.

A formal analysis of alexia in persistent aura and a comparison to acquired pure alexia

A patient is reported with reversible pure alexia in the context of migraine with aura. Following previous, anecdotal reports, the present study is the first to formally assess word reading, writing, and other linguistic and visual processing and to compare these to a patient with stroke-related pure alexia. The reading impairment, suggestive of letter-by-letter reading, was observed across 7 days but had remitted at a 3-month follow-up. The deficit also affected recognition of letters, suggesting a functional impairment at the level of letter recognition, not just word reading. It went along with reversible abnormalities in diffusion-weighted and fluid-attenuated inversion recovery imaging in areas known to be involved in word reading.

Cognitive neuropsychological analysis of differential reading and spelling disorder mechanisms in a patient with aphasia

The purpose of this study was to determine if differential reading and spelling mechanisms were involved in a Japanese patient with aphasia. In our case, the patient scored low on all of the administered reading tasks, suggesting that both the reading lexical and non-lexical routes were impaired. In contrast, his writing-to-dictation score for Kana nonwords was high, suggesting that the spelling non-lexical route was intact. However, the patient scored low on a writing-to-dictation task comprised of high-familiarity Kanji words. The spelling lexical route was thought to be impaired. Therefore, the mechanism(s) involved in reading and spelling may differ in this case.

Treatment for Alexia With Agraphia Following Left Ventral Occipito-Temporal Damage: Strengthening Orthographic Representations Common to Reading and Spelling

PURPOSE

Damage to left ventral occipito-temporal cortex can give rise to written language impairment characterized by pure alexia/letter-by-letter (LBL) reading, as well as surface alexia and agraphia. The purpose of this study was to examine the therapeutic effects of a combined treatment approach to address concurrent LBL reading with surface alexia/agraphia.

METHOD

Simultaneous treatment to address slow reading and errorful spelling was administered to 3 individuals with reading and spelling impairments after left ventral occipito-temporal damage due to posterior cerebral artery stroke. Single-word reading/spelling accuracy, reading latencies, and text reading were monitored as outcome measures for the combined effects of multiple oral re-reading treatment and interactive spelling treatment.

RESULTS

After treatment, participants demonstrated faster and more accurate single-word reading and improved text-reading rates. Spelling accuracy also improved, particularly for untrained irregular words, demonstrating generalization of the trained interactive spelling strategy.

CONCLUSION

This case series characterizes concomitant LBL with surface alexia/agraphia and demonstrates a successful treatment approach to address both the reading and spelling impairment.

Selective Neural Synchrony Suppression as a Forward Gatekeeper to Piecemeal Conscious Perception

The emergence of conscious visual perception is assumed to ignite late (∼250 ms) gamma-band oscillations shortly after an initial (∼100 ms) forward sweep of neural sensory (nonconscious) information. However, this neural evidence is not utterly congruent with rich behavioral data which rather point to piecemeal (i.e., graded) perceptual processing. To address the unexplored neural mechanisms of piecemeal ignition of conscious perception, hierarchical script sensitivity of the putative visual word form area (VWFA) was exploited to signal null (i.e., sensory), partial (i.e., letter-level), and full (i.e., word-level) conscious perception. Two magnetoencephalography experiments were conducted in which healthy human participants viewed masked words (Experiment I: active task, Dutch words; Experiment II: passive task, Hebrew words) while high-frequency (broadband gamma) brain activity was measured. Findings revealed that piecemeal conscious perception did not ignite a linear piecemeal increase in oscillations. Instead, whereas late (∼250 ms) gamma-band oscillations signaled full conscious perception (i.e., word-level), partial conscious perception (i.e., letter-level) was signaled via the inhibition of the early (∼100 ms) forward sweep. This inhibition regulates the downstream broadcast to filter out irrelevant (i.e., masks) information. The findings thus highlight a local (VWFA) gatekeeping mechanism for conscious perception, operating by filtering out and in selective percepts.

Aphasia, Alexia, and Oral Reading

Alexia is an acquired disturbance in reading. Alexias that occur after left hemisphere damage typically result from linguistic deficits and may occur as isolated symptoms or as part of an aphasia syndrome. This article presents an overview of the classification of the alexias, including both the traditional neuroanatomical perspective and the more recent psycholinguistic approach. Then, assessment procedures are reviewed, followed by a summary of treatment approaches for alexia. Finally, two case studies illustrate how oral reading of connected language (sentences and paragraphs rather than single words) has been used as a technique for treating alexia in patients with aphasia.

Fast word reading in pure alexia: "fast, yet serial"

Pure alexia is a severe impairment of word reading in which individuals process letters serially with a pronounced length effect. Yet, there is considerable variation in the performance of alexic readers with generally very slow, but also occasionally fast responses, an observation addressed rarely in previous reports. It has been suggested that "fast" responses in pure alexia reflect residual parallel letter processing or that they may even be subserved by an independent reading system. Four experiments assessed fast and slow reading in a participant (DN) with pure alexia. Two behavioral experiments investigated frequency, neighborhood, and length effects in forced fast reading. Two further experiments measured eye movements when DN was forced to read quickly, or could respond faster because words were easier to process. Taken together, there was little support for the proposal that "qualitatively different" mechanisms or reading strategies underlie both types of responses in DN. Instead, fast responses are argued to be generated by the same serial-reading strategy.

Neural correlates of spelling difficulties in Alzheimer's disease

Alzheimer's disease (AD) is associated with a general cognitive decline that affects the memory and language domains. Thus, an oral production deficit with a lexical-semantic origin has been widely observed in these patients. Their written production capacities, however, have been much less studied. We assessed the spelling abilities of 22 AD patients and a group of matched healthy controls with a test battery including written picture naming and word and pseudoword dictation tests, as well as text dictation and spontaneous writing tasks. The results of the AD patients in the discriminative tasks were then entered into voxel-based morphometry analyses along with their grey matter volumes. The patient group presented a selective impairment for word dictation, which contrasted with a spared capacity to spell pseudowords, and showed more difficulties for words with arbitrary and rule-based orthography. Moreover, they also produced less complete syntactic units in the spontaneous writing task. These results point out the lexical-semantic, as opposed to sublexical, nature of the spelling deficit associated to AD. In addition, we recognized a mainly left-lateralized cortical network, including areas in the posterior inferior temporal lobe and the superior region of the parietal cortex, which might be responsible for this impairment. Other regions, such as the putamen, were also associated to the deficit. The results of this study, hence, improve our understanding of the neuropsychological and neuroanatomical mechanisms that underlie the cognitive symptoms associated to AD.

An eye movement study on the role of the visual field defect in pure alexia

Pure alexia is a severe impairment of word reading which is usually accompanied by a right-sided visual field defect. Patients with pure alexia exhibit better preserved writing and a considerable word length effect, claimed to result from a serial letter processing strategy. Two experiments compared the eye movements of four patients with pure alexia to controls with simulated visual field defects (sVFD) when reading single words. Besides differences in response times and differential effects of word length on word reading in both groups, fixation durations and the occurrence of a serial, letter-by-letter fixation strategy were investigated. The analyses revealed quantitative and qualitative differences between pure alexic patients and unimpaired individuals reading with sVFD. The patients with pure alexia read words slower and exhibited more fixations. The serial, letter-by-letter fixation strategy was observed only in the patients but not in the controls with sVFD. It is argued that the VFD does not cause pure alexic reading.

On compensatory strategies and computational models: the case of pure alexia

The article is concerned with inferences from the behaviour of neurological patients to models of normal function. It takes the letter-by-letter reading strategy common in pure alexic patients as an example of the methodological problems involved in making such inferences that compensatory strategies produce. The evidence is discussed on the possible use of three ways the letter-by-letter reading process might operate: "reversed spelling"; the use of the phonological input buffer as a temporary holding store during word building; and the use of serial input to the visual word-form system entirely within the visual-orthographic domain such as in the model of Plaut [1999. A connectionist approach to word reading and acquired dyslexia: Extension to sequential processing. Cognitive Science, 23, 543-568]. The compensatory strategy used by, at least, one pure alexic patient does not fit with the third of these possibilities. On the more general question, it is argued that even if compensatory strategies are being used, the behaviour of neurological patients can be useful for the development and assessment of first-generation information-processing models of normal function, but they are not likely to be useful for the development and assessment of second-generation computational models.

Prelexical representations and processes in reading: evidence from acquired dyslexia

We report a detailed and extensive single-case study of an acquired dyslexic patient, L.H.D., who suffered a left-hemisphere lesion as a result of a ruptured aneurysm. We present evidence that L.H.D.'s reading errors stem from a deficit in visual letter identification, and we use her deficit as a basis for exploring a variety of issues concerning prelexical representations and processes in reading. First, building on the work of other researchers, we present evidence that the prelexical reading system includes an allograph level of representation that represents each distinct visual shape of a letter (e.g., a, A, etc., for the letter A). We extend a theory proposed by Caramazza and Hillis [Caramazza, A., & Hillis, A. (1990a). Spatial representation of words in the brain implied by studies of a unilateral neglect patient. Nature, 346, 267-269] to include an allograph level, and we probe the nature of the allograph representations in some detail. Next, we explore the implications of visual similarity effects and letter perseverations in L.H.D.'s reading performance, arguing that these effects shed light on activation dynamics in the prelexical reading system and on the genesis of L.H.D.'s errors. We also probe the processing of letter case in the visual letter identification process, proposing that separate abstract letter identity and case representations are computed. Finally, we present evidence that the allograph level as well as the abstract letter identity level implement a word-based frame of reference.

What lies beneath: a comparison of reading aloud in pure alexia and semantic dementia

Exaggerated effects of word length upon reading-aloud performance define pure alexia, but have also been observed in semantic dementia. Some researchers have proposed a reading-specific account, whereby performance in these two disorders reflects the same cause: impaired orthographic processing. In contrast, according to the primary systems view of acquired reading disorders, pure alexia results from a basic visual processing deficit, whereas degraded semantic knowledge undermines reading performance in semantic dementia. To explore the source of reading deficits in these two disorders, we compared the reading performance of 10 pure alexic and 10 semantic dementia patients, matched in terms of overall severity of reading deficit. The results revealed comparable frequency effects on reading accuracy, but weaker effects of regularity in pure alexia than in semantic dementia. Analysis of error types revealed a higher rate of letter-based errors and a lower rate of regularization responses in pure alexia than in semantic dementia. Error responses were most often words in pure alexia but most often nonwords in semantic dementia. Although all patients made some letter substitution errors, these were characterized by visual similarity in pure alexia and phonological similarity in semantic dementia. Overall, the data indicate that the reading deficits in pure alexia and semantic dementia arise from impairments of visual processing and knowledge of word meaning, respectively. The locus and mechanisms of these impairments are placed within the context of current connectionist models of reading.

Brain mechanisms and reading remediation: more questions than answers

Dyslexia is generally diagnosed in childhood and is characterised by poor literacy skills with associated phonological and perceptual problems. Compensated dyslexic readers are adult readers who have a documented history of childhood dyslexia but as adults can read and comprehend written text well. Uncompensated dyslexic readers are adults who similarly have a documented history of reading impairment but remain functionally reading-impaired all their lives. There is little understanding of the neurophysiological basis for how or why some children become compensated, while others do not, and there is little knowledge about neurophysiological changes that occur with remedial programs for reading disability. This paper will review research looking at reading remediation, particularly in the context of the underlying neurophysiology.

Sequential then interactive processing of letters and words in the left fusiform gyrus

Despite decades of cognitive, neuropsychological and neuroimaging studies, it is unclear if letters are identified before word-form encoding during reading, or if letters and their combinations are encoded simultaneously and interactively. Here using functional magnetic resonance imaging, we show that a 'letter-form' area (responding more to consonant strings than false fonts) can be distinguished from an immediately anterior 'visual word-form area' in ventral occipito-temporal cortex (responding more to words than consonant strings). Letter-selective magnetoencephalographic responses begin in the letter-form area ∼60 ms earlier than word-selective responses in the word-form area. Local field potentials confirm the latency and location of letter-selective responses. This area shows increased high-gamma power for ∼400 ms, and strong phase-locking with more anterior areas supporting lexico-semantic processing. These findings suggest that during reading, visual stimuli are first encoded as letters before their combinations are encoded as words. Activity then rapidly spreads anteriorly, and the entire network is engaged in sustained integrative processing.

Intact reading in patients with profound early visual dysfunction

Despite substantial neuroscientific evidence for a region of visual cortex dedicated to the processing of written words, many studies continue to reject explanations of letter-by-letter (LBL) reading in terms of impaired word form representations or parallel letter processing in favour of more general deficits of visual function. In the current paper, we demonstrate that whilst LBL reading is often associated with general visual deficits, these deficits are not necessarily sufficient to cause reading impairment and have led to accounts of LBL reading which are based largely on evidence of association rather than causation. We describe two patients with posterior cortical atrophy (PCA) who exhibit remarkably preserved whole word and letter reading despite profound visual dysfunction. Relative to controls, both patients demonstrated impaired performance on tests of early visual, visuoperceptual and visuospatial processing; visual acuity was the only skill preserved in both individuals. By contrast, both patients were able to read aloud words with perfect to near-perfect accuracy. Reading performance was also rapid with no overall significant difference in response latencies relative to age- and education-matched controls. Furthermore, the patients violated a key prediction of general visual accounts of LBL reading – that pre-lexical impairments should result in prominent word length effects; in the two reported patients, evidence for abnormal word length effects was equivocal or absent, and certainly an order of magnitude different to that reported for LBL readers. We argue that general visual accounts cannot explain the pattern of reading data reported, and attribute the preserved reading performance to preserved direct access to intact word form representations and/or parallel letter processing mechanisms. The current data emphasise the need for much clearer evidence of causality when attempting to draw connections between specific aspects of visual processing and different types of acquired peripheral dyslexia.

Recovery in a letter-by-letter reader: more efficiency at the expense of normal reading strategy

Although changes in reading performance of recovering letter-by-letter readers have been described in some detail, no prior research has provided an in-depth analysis of the underlying adaptive word processing strategies. Our work examined the reading performance of a letter-by-letter reader, FH, over a period of 15 months, using eye movement methodology to delineate the recovery process at two different time points (T1, T2). A central question is whether recovery is characterized either by moving back towards normal word processing or by refinement and possibly automatization of an existing pathological strategy that was developed in response to the impairment. More specifically, we hypothesized that letter-by-letter reading may be executed with at least four different strategies and our work sought to distinguish between these alternatives. During recovery significant improvements in reading performance were achieved. A shift of fixation positions from the far left to the extreme right of target words was combined with many small and very few longer regressive saccades. Apparently, 'letter-by-letter reading' took the form of local clustering, most likely corresponding to the formation of sublexical units of analysis. This pattern was more pronounced at T2, suggesting that improvements in reading efficiency may come at the expense of making it harder to eventually return to normal reading.

Phonological activation in pure alexia

Pure alexia is a reading impairment in which patients appear to read letter-by-letter. This disorder is typically accounted for in terms of a peripheral deficit that occurs early on in the reading system, prior to the activation of orthographic word representations. The peripheral interpretation of pure alexia has recently been challenged by the phonological deficit hypothesis, which claims that a postlexical disconnection between orthographic and phonological information contributes to or is responsible for the disorder. Because this hypothesis was mainly supported by data from a single patient (IH), who also has surface dyslexia, the present study re-examined this hypothesis with another pure alexic patient (EL). In contrast to patient IH, EL did not show any evidence of a phonological deficit. Her pattern of performance in naming was not qualitatively different from that of normal readers; she appeared to be reading via a mode of processing resulting in strong serial and lexical effects, a pattern often observed in normal individuals reading unfamiliar stimuli. The present results do not obviously support the phonological hypothesis and are more consistent with peripheral interpretations of pure alexia. The peripheral and the phonological accounts of pure alexia are discussed in light of two current models of visual word recognition.

Pure alexia and covert reading: Evidence from Stroop tasks

Patients with pure alexia (also referred to as letter-by-letter readers) show a marked word-length effect when naming visually presented words, evidenced by a monotonic increase in response time (or decrease in accuracy) as a function of the number of letters in the string. Interestingly, despite the difficulty in overtly reporting the identity of some words, many patients exhibit fast and above-chance access to lexical and/or semantic information for the same words. To explore the extent of this covert reading, we examined the degree of interference afforded by the inconsistent (word identity and colour label do not match) versus neutral condition in a Stroop task in a pure alexic patient, EL. EL shows evidence of covert reading on a semantic categorisation task and a lexical decision task. She also demonstrates covert reading by exhibiting Stroop interference of the same magnitude as a matched control subject, when naming the colour of the ink in which a word is printed. When the word shares some but not all letters with the colour name (BLOW instead of BLUE), neither subject shows interference. In contrast with the control subject, EL does not show Stroop interference when various orthographic changes (degraded visual input, cursive font) or phonological or semantic changes are made to the word. These findings indicate that although some implicit processing of words may be possible, this processing is rather rudimentary. Not surprising, this implicit activation may be insufficient to support overt word identification. We explain these findings in the context of a single, integrated account of pure alexia.

Sequential and parallel letter processing in letter-by-letter dyslexia

Four experiments are reported that focus on the issue of sequential vs. parallel letter processing in letter-by-letter (LBL) dyslexia; these were conducted on patient IH. Expt. 1 showed a large linear reduction of word naming times with an increase in the number of orthographic neighbours of the target (i.e., words of the same length differing by just one letter; N size). Given the large negative linear correlation existing between word length and N size, this result raises the possibility that the large word length effect diagnostic of LBL dyslexia may be, in fact, an artefact of uncontrolled N size. Expt. 2 falsified this possibility by showing that the word length effect is unaffected by whether N size is controlled for or not. This result also suggested that the facilitatory effect of increased N size in LBL dyslexia is based on the parallel processing of the constituent letters of the target. Further supporting a contribution of parallel letter processing to overt word recognition performance in the disorder, Expt. 3 showed significant but independent effects of word length and letter confusability (i.e., similarity of the constituent letters of the target word with other letters of the alphabet). The letter confusability effect therefore appears to rest on the parallel analysis of the letters in the target word. Finally, Expt. 4 showed that the facilitatory effect of N size is prevented with high letter-confusability targets. These observations suggest that LBL dyslexia rests on an impairment of letter encoding that results in an excessive level of background noise in the activation of lexical-orthographic representations when letters are processed in parallel. This prevents overt identification of the target and forces sequential letter processing in order to achieve this goal.

Reading without the left ventral occipito-temporal cortex

The left ventral occipito-temporal cortex (LvOT) is thought to be essential for the rapid parallel letter processing that is required for skilled reading. Here we investigate whether rapid written word identification in skilled readers can be supported by neural pathways that do not involve LvOT. Hypotheses were derived from a stroke patient who acquired dyslexia following extensive LvOT damage. The patient followed a reading trajectory typical of that associated with pure alexia, re-gaining the ability to read aloud many words with declining performance as the length of words increased. Using functional MRI and dynamic causal modelling (DCM), we found that, when short (three to five letter) familiar words were read successfully, visual inputs to the patient’s occipital cortex were connected to left motor and premotor regions via activity in a central part of the left superior temporal sulcus (STS). The patient analysis therefore implied a left hemisphere “reading-without-LvOT” pathway that involved STS. We then investigated whether the same reading-without-LvOT pathway could be identified in 29 skilled readers and whether there was inter-subject variability in the degree to which skilled reading engaged LvOT. We found that functional connectivity in the reading-without-LvOT pathway was strongest in individuals who had the weakest functional connectivity in the LvOT pathway. This observation validates the findings of our patient’s case study. Our findings highlight the contribution of a left hemisphere reading pathway that is activated during the rapid identification of short familiar written words, particularly when LvOT is not involved. Preservation and use of this pathway may explain how patients are still able to read short words accurately when LvOT has been damaged.

"Serial" effects in parallel models of reading

There is now considerable evidence showing that the time to read a word out loud is influenced by an interaction between orthographic length and lexicality. Given that length effects are interpreted by advocates of dual-route models as evidence of serial processing this would seem to pose a serious challenge to models of single word reading which postulate a common parallel processing mechanism for reading both words and nonwords (Coltheart, Rastle, Perry, Langdon, & Ziegler, 2001; Rastle, Havelka, Wydell, Coltheart, & Besner, 2009). However, an alternative explanation of these data is that visual processes outside the scope of existing parallel models are responsible for generating the word-length related phenomena (Seidenberg & Plaut, 1998). Here we demonstrate that a parallel model of single word reading can account for the differential word-length effects found in the naming latencies of words and nonwords, provided that it includes a mapping from visual to orthographic representations, and that the nature of those orthographic representations are not preconstrained. The model can also simulate other supposedly "serial" effects. The overall findings were consistent with the view that visual processing contributes substantially to the word-length effects in normal reading and provided evidence to support the single-route theory which assumes words and nonwords are processed in parallel by a common mechanism.

Covert reading of letters in a case of global alexia

This study describes the case of a global alexic patient with a severe reading deficit affecting words, letters and Arabic numbers, following a left posterior lesion. The patient (VA) could not match spoken letters to their graphic form. A preserved ability to recognize shape and canonical orientation of letters indicates intact access to the representation of letters and numbers as visual objects. A relatively preserved ability to match lowercase to uppercase letters suggests partially spared access to abstract letter identities independently of their visual forms. The patient was also unable to match spoken letters and numbers to their visual form, indicating that she could not access the graphemic representations of letters from their phonological representations. This pattern of performance suggests that the link between graphemic and phonological representations is disrupted in this patient. We hypothesize that VA' residual reading abilities are supported by the right hemisphere.

The multiple-lemma representation of Italian compound nouns: a single case study of deep dyslexia

It is not clear how compound words are represented within the influential framework of the lemma-lexeme theory. Theoretically, compounds could be structured through a multiple lemma architecture, in which the lemma nodes of both the compound and its constituents are involved in lexical processing. If this were the case, syntactic properties of both the compound and its constituents should play a role when performing tasks involving compound processing, e.g., compound-word reading. This issue is investigated in the present study through an assessment of the performance of a deep dyslexic patient (GR) in three compound-reading experiments. In the first experiment, verb-noun (VN) compound nouns (e.g., lavapiatti, "dishwasher", lit. wash-dishes) were employed as stimuli, while in the second, VN compound stimuli were embedded in sentences, and were compared to paired verb phrases (e.g., lui lava piatti, "he washes dishes"). Position-specific effects were ruled out by means of a third experiment, which investigated the retrieval of noun-noun compounds (e.g., pescespada, "swordfish", lit. fishsword). In experiment 1, GR made errors on the verb constituent more frequently than on the noun, an effect that did not emerge in Experiment 2: when embedded in sentences, VN compounds were read significantly better than verb-phrases and no grammatical-class effect emerged. In Experiment 3, the first and the second constituent were read with the same level of accuracy. The disproportionate impairment, which emerged in reading the verb component of nominal VN compounds, indicates that the grammatical properties of constituents are being retrieved, and thus confirms access to the constituent lemma-nodes. However, the results suggested a whole-word representation when compounds are embedded in sentences; since the sentence context affects the access to compounds through syntactic constraints, whole-word representation is arguably at the lemma level as well (multiple-lemma representation). Experiment 3 indicates that these effects cannot be accounted for by a position-specific impairment.

Multimodal alexia: neuropsychological mechanisms and implications for treatment

Letter-by-letter (LBL) reading is the phenomenon whereby individuals with acquired alexia decode words by sequential identification of component letters. In cases where letter recognition or letter naming is impaired, however, a LBL reading approach is obviated, resulting in a nearly complete inability to read, or global alexia. In some such cases, a treatment strategy wherein letter tracing is used to provide tactile and/or kinesthetic input has resulted in improved letter identification. In this study, a kinesthetic treatment approach was implemented with an individual who presented with severe alexia in the context of relatively preserved recognition of orally spelled words, and mildly impaired oral/written spelling. Eight weeks of kinesthetic treatment resulted in improved letter identification accuracy and oral reading of trained words; however, the participant remained unable to successfully decode untrained words. Further testing revealed that, in addition to the visual-verbal disconnection that resulted in impaired word reading and letter naming, her limited ability to derive benefit from the kinesthetic strategy was attributable to a disconnection that prevented access to letter names from kinesthetic input. We propose that this kinesthetic-verbal disconnection resulted from damage to the left parietal lobe and underlying white matter, a neuroanatomical feature that is not typically observed in patients with global alexia or classic LBL reading. This unfortunate combination of visual-verbal and kinesthetic-verbal disconnections demonstrated in this individual resulted in a persistent multimodal alexia syndrome that was resistant to behavioral treatment. To our knowledge, this is the first case in which the nature of this form of multimodal alexia has been fully characterized, and our findings provide guidance regarding the requisite cognitive skills and lesion profiles that are likely to be associated with a positive response to tactile/kinesthetic treatment.

Age-of-Acquisition Effects in Pure Alexia

Pure alexia is an acquired reading disorder in which previously literate adults adopt a letter-by-letter processing strategy. Though these individuals display impaired reading, research shows that they are still able to use certain lexical information in order to facilitate visual word processing. The current experiment investigates the role that a word's age of acquisition (AoA) plays in the reading processes of an individual with pure alexia (G.J.) when other lexical variables have been controlled. Results from a sentence reading task in which eye movement patterns were recorded indicated that G.J. shows a strong effect of AoA, where late-acquired words are more difficult to process than early-acquired words. Furthermore, it was observed that the AoA effect is much greater for G.J. than for age-matched control participants. This indicates that patients with pure alexia rely heavily on intact top-down information, supporting the interactive activation model of reading.

Number reading in pure alexia--a review

It is commonly assumed that number reading can be intact in patients with pure alexia, and that this dissociation between letter/word recognition and number reading strongly constrains theories of visual word processing. A truly selective deficit in letter/word processing would strongly support the hypothesis that there is a specialized system or area dedicated to the processing of written words. To date, however, there has not been a systematic review of studies investigating number reading in pure alexia and so the status of this assumed dissociation is unclear. We review the literature on pure alexia from 1892 to 2010, and find no well-documented classical dissociation between intact number reading and impaired letter identification in a patient with pure alexia. A few studies report strong dissociations, with number reading less impaired than letter reading, but when we apply rigorous statistical criteria to evaluate these dissociations, the difference in performance across domains is not statistically significant. There is a trend in many cases of pure alexia, however, for number reading to be less affected than letter identification and word reading. We shed new light on this asymmetry by showing that, under conditions of brief exposure, normal participants are also better at identifying digits than letters. We suggest that the difference observed in some pure alexic patients may possibly reflect an amplification of this normal difference in the processing of letters and digits, and we relate this asymmetry to intrinsic differences between the two types of symbols.

Amblyopic dyslexia: a little investigated reading disorder

We present a case of a little investigated reading disorder we call 'amblyopic dyslexia'. The reading impairment in this patient resulted from a left extrastriate and white matter lesion causing a scotomatic area of partial deficit within the right visual field. The visual deficit was consistent with cerebral amblyopia, that is, reduced form, colour, and light sensitivity without a complete loss of vision. The patient's reading deficit was characterized by accurate single letter naming and almost accurate but effortful single word reading, with no letter-by-letter strategy. The criteria for distinguishing amblyopic dyslexia from other reading disorders and the most appropriate treatment are discussed.

Spelling and reading: using visual sensitivity to explore shared or separate orthographic representations

Do we use the same neurocognitive mechanisms to spell that we do to read? There is a considerable number of conflicting findings, such that evidence has been provided to support common mechanisms for reading and spelling, while other research supports the proposal that reading and spelling utilise unique neurocognitive resources. Sensitivity to visual spatial-frequency doubling (FD) has been demonstrated to correlate with and specifically predict orthographic processing when reading; therefore, if spelling and reading share some elements of orthographic representation, sensitivity to FD should similarly correlate with, and predict, spelling ability by virtue of this shared association. A double dissociation between reading and spelling was found such that sensitivity to the FD task, as mediated by the visual dorsal stream, predicted reading ability but not spelling, while the visual control task predicted spelling but not reading ability, in poor readers/spellers. The results support a dual-orthographic model with separate orthographic representations for reading and spelling.

When does less yield more? The impact of severity upon implicit recognition in pure alexia

Pure alexia (PA) is characterised by strong effects of word length on reading times and is sometimes accompanied by an overt letter-by-letter (LBL) reading strategy. Past studies have reported "implicit recognition" in some individual PA patients. This is a striking finding because such patients are able to perform semantic classification and lexical decision at above chance levels even when the exposure duration is short enough to prevent explicit identification. In an attempt to determine the prevalence of this "implicit recognition" effect, we assessed semantic categorisation and lexical decision performance using limited exposure durations in 10 PA cases. The majority of the patients showed above chance accuracy in semantic categorisation and lexical decision. Performance on the lexical decision test was influenced by frequency and imageability. In addition, we found that the extent to which patients showed evidence of "implicit recognition" in both tasks was inversely related to the severity of their reading disorder. This result is consistent with hypotheses which suggest that this effect does not constitute an implicit form of unique word identification but is a reflection of the degree of partial activation within the word recognition system. These results also go some way towards explaining the individual variation in the presence of this effect observed across previous case-study investigations in the literature.

The relationship between visual crowding and letter confusability: towards an understanding of dyslexia in posterior cortical atrophy

Visual crowding is a form of masking in which target identification is hindered by excessive feature integration from other stimuli in the vicinity. It has previously been suggested that excessive visual crowding constitutes one specific form of early-visual-processing deficit, which may be observed in individuals with posterior cortical atrophy (PCA). This study investigated whether excessive visual crowding plays a significant role in the acquired dyslexia of two PCA patients, whose reading was characterized by visual paralexias. The patients were administered a series of letter, flanked letter, and word recognition tasks, and the effects of letter spacing and letter confusability upon response accuracy and latency were measured. In both patients, the results showed (a) evidence of excessive visual crowding, (b) a significant interaction between letter spacing and confusability on flanked letter identification tasks, and (c) effects of letter confusability affecting flanked but not unflanked letter identification. However, only mild improvements in reading accuracy were achieved in the experimental manipulations of interletter spacing within words because these manipulations had a dual effect: Increasing spacing improved individual letter identification but damaged whole-word form and/or parallel letter processing. We consider the implications of these results for the characterization of dyslexia in PCA, the design of reading rehabilitation strategies, and the relationship between visual crowding and letter confusability. In particular, we argue that the reading deficits observed in our patients cannot be accounted for solely in terms of a very low signal-to-noise ratio for letter identification, and that an additional crowding deficit is implicated in which excessive integration of fundamental letter features leads to the formation of incorrect letter percepts.