Phonological Dyslexia

A case of acquired phonological dyslexia with selective impairment of Kanji: analysis of reading impairment mechanism using cognitive neuropsychological models for reading

We report a Japanese-speaking patient who showed acquired phonological dyslexia only in Kanji; difficulty in reading two-character Kanji nonwords despite her ability to read Kana nonwords, Kana words, and two-character Kanji inconsistent-atypical words; and inability to repeat reversal nonwords. We investigated the mechanism of nonword reading impairment using the dual-route cascaded model, it was likely that the reading deficit of Kanji nonwords with multiple pronunciations resulted from the dysfunction of the character-to-sound conversion rule system. The patient's reading performance on the dissociation of Kana and Kanji was considered to reflect the difference in the consistency of orthography-to-phonology mapping.

Pseudoword spelling ability predicts response to word spelling treatment in acquired dysgraphia

Although rehabilitation of acquired dysgraphia can be quite effective, identifying predictors of responsiveness to treatment is useful for prognosis and individualization of treatment protocols. This study examined whether various features of treatment response were predicted by the integrity of one or more of the central cognitive components of spelling: orthographic long-term memory, orthographic working memory, and phoneme-grapheme conversion. Twenty dysgraphic individuals received 12 weeks of bi-weekly, individualized, lexically-based spelling rehabilitation using a spell-study-spell paradigm. Linear multiple regression modelling examined whether the type and severity of the dysgraphic deficit, assessed before rehabilitation, predicted the magnitude and rate of improvement, generalization to untrained items and maintenance of treatment gains. The results revealed that pseudoword spelling accuracy - indexing the integrity of the phoneme-grapheme conversion system - was the only factor examined that significantly predicted the rate of accuracy gains for trained words as well as the extent of generalization to untrained words. Pre-treatment pseudoword spelling accuracy also predicted retention of gains for trained and untrained words at 3-month follow-up. These findings reveal that the integrity of the phoneme-grapheme conversion system prior to dysgraphia rehabilitation may play a key role in rehabilitation-driven recovery, even when the treatment approach targets lexical rather than pseudoword spelling processes.

Reading and visual word recognition ability in semantic dementia is not predicted by semantic performance

This paper describes longitudinal testing of two Semantic Dementia (SD) cases. It is common for patients with SD to present with deficits in reading aloud irregular words (i.e. surface dyslexia), and in lexical decision. Theorists from the connectionist tradition (e.g. Woollams et al., 2007) argue that in SD cases with concurrent surface dyslexia, the deterioration of irregular word reading and recognition performance is related to the extent of the deterioration of the semantic system. The Dual Route Cascaded model (DRC; Coltheart et al., 2001) makes no such prediction. We examined this issue using a battery of cognitive tests and two structural scans undertaken at different points in each cases time course. Across both cases, our behavioural testing found little evidence of a key putative link between semantic impairment and the decline of irregular word reading or lexical decision. In addition, our neuroimaging analyses suggested that it may be the emergence of atrophy to key neural regions both inside and outside the anterior temporal lobes that may best capture the emergence of impairments of irregular word reading, and implicated inferior temporal cortex in surface dyslexia.

The anatomical foundations of acquired reading disorders: a neuropsychological verification of the dual-route model of reading

In this study we investigated the neural correlates of acquired reading disorders through an anatomo-correlative procedure of the lesions of 59 focal brain damaged patients suffering from acquired surface, phonological, deep, undifferentiated dyslexia and pure alexia. Two reading tasks, one of words and nonwords and one of words with unpredictable stress position, were used for this study. We found that surface dyslexia was predominantly associated with left temporal lesions, while in phonological dyslexia the lesions overlapped in the left insula and the left inferior frontal gyrus (pars opercularis) and that pure alexia was associated with lesions in the left fusiform gyrus. A number of areas and white matter tracts, which seemed to involve processing along both the lexical and the sublexical routes, were identified for undifferentiated dyslexia. Two cases of deep dyslexia with relatively dissimilar anatomical correlates were studied, one compatible with Coltheart's right-hemisphere hypothesis (1980) whereas the other could be interpreted in the context of Morton and Patterson's (1980), multiply-damaged left-hemisphere hypothesis. In brief, the results of this study are only partially consistent with the current state of the art, and propose new and stimulating challenges; indeed, based on these results we suggest that different types of acquired dyslexia may ensue after different cortical damage, but white matter disconnection may play a crucial role in some cases.

CDP++.Italian: modelling sublexical and supralexical inconsistency in a shallow orthography

Most models of reading aloud have been constructed to explain data in relatively complex orthographies like English and French. Here, we created an Italian version of the Connectionist Dual Process Model of Reading Aloud (CDP++) to examine the extent to which the model could predict data in a language which has relatively simple orthography-phonology relationships but is relatively complex at a suprasegmental (word stress) level. We show that the model exhibits good quantitative performance and accounts for key phenomena observed in naming studies, including some apparently contradictory findings. These effects include stress regularity and stress consistency, both of which have been especially important in studies of word recognition and reading aloud in Italian. Overall, the results of the model compare favourably to an alternative connectionist model that can learn non-linear spelling-to-sound mappings. This suggests that CDP++ is currently the leading computational model of reading aloud in Italian, and that its simple linear learning mechanism adequately captures the statistical regularities of the spelling-to-sound mapping both at the segmental and supra-segmental levels.

Left- and right-hemisphere forms of phonological alexia

We studied the ability of patients with lesions arising from operation for an anterior or posterior (left or right) brain tumour to read a set of words and pronounceable nonwords. In line with previous works, we observed that damage to the left posterior or left anterior cortex can give rise to phonological alexia, where the reading performance of nonwords is affected more than that of words. More surprisingly, similar effects were found in the right posterior group. However, there were significant differences in the error types, for both complex and positional errors, between phonological alexic patients in the three location groups. The findings present difficulties for the position held by theorists of the triangle model that phonological alexia arises from impairments in the language production system or in a general-purpose orthographic-phonological translation system. They also pose new questions about the possible role of the right posterior cortex in letter sequence representation.

The role of plasticity-related functional reorganization in the explanation of central dyslexias

This investigation explored the hypothesis that patterns of acquired dyslexia may reflect, in part, plasticity-driven relearning that dynamically alters the division of labour (DOL) between the direct, orthography → phonology (O → P) pathway and the semantically mediated, orthography → semantics → phonology (O → S → P) pathway. Three simulations were conducted using a variant of the triangle model of reading. The model demonstrated core characteristics of normal reading behaviour in its undamaged state. When damage was followed by reoptimization (mimicking spontaneous recovery), the model reproduced the deficits observed in the central dyslexias-acute phonological damage combined with recovery matched data taken from a series of 12 phonological dyslexic patients-whilst progressive semantic damage interspersed with recovery reproduced data taken from 100 observations of semantic dementia patients. The severely phonologically damaged model also produced symptoms of deep dyslexia (imageability effects, production of semantic and mixed semantic/visual errors). In all cases, the DOL changed significantly in the recovery period, suggesting that postmorbid functional reorganization is important in understanding behaviour in chronic-stage patients.

Written language impairments in primary progressive aphasia: a reflection of damage to central semantic and phonological processes

Connectionist theories of language propose that written language deficits arise as a result of damage to semantic and phonological systems that also support spoken language production and comprehension, a view referred to as the "primary systems" hypothesis. The objective of the current study was to evaluate the primary systems account in a mixed group of individuals with primary progressive aphasia (PPA) by investigating the relation between measures of nonorthographic semantic and phonological processing and written language performance and by examining whether common patterns of cortical atrophy underlie impairments in spoken versus written language domains. Individuals with PPA and healthy controls were administered a language battery, including assessments of semantics, phonology, reading, and spelling. Voxel-based morphometry was used to examine the relation between gray matter volumes and language measures within brain regions previously implicated in semantic and phonological processing. In accordance with the primary systems account, our findings indicate that spoken language performance is strongly predictive of reading/spelling profile in individuals with PPA and suggest that common networks of critical left hemisphere regions support central semantic and phonological processes recruited for spoken and written language.

Computational modelling of phonological dyslexia: how does the DRC model fare?

This paper investigates the patterns of reading impairment in phonological dyslexia using computational modelling with the dual-route cascaded model of reading (DRC, Coltheart, Rastle, Perry, Langdon, & Ziegler, 2001). Systematic lesioning of nonlexical and phonological processes in DRC demonstrates that different lesions and severity of those lesions can reproduce features of phonological dyslexia including impaired reading of nonwords, relatively spared reading of words, an advantage for reading pseudohomophones. Using the same stimuli for model and for patients, lesions to DRC were also used to simulate the reading accuracy shown by three individuals with acquired phonological dyslexia. No single lesion could replicate the reading performance of all three individuals. In order to simulate reading accuracy for one individual a phonological impairment was necessary (addition of noise to the phoneme units), and for the remaining two individuals an impairment to nonlexical reading procedures (increasing the time interval between each new letter being processed) was necessary. We argue that no single locus of impairment (neither phonological nor nonlexical) can account for the reading impairments of all individuals with phonological dyslexia. Instead, different individuals have different impairments (and combinations of impairments) that together provide the spectrum of patterns found in phonological dyslexia.

Phonological dyslexia and dysgraphia: cognitive mechanisms and neural substrates

To examine the validity of different theoretical assumptions about the neuropsychological mechanisms and lesion correlates of phonological dyslexia and dysgraphia, we studied written and spoken language performance in a large cohort of patients with focal damage to perisylvian cortical regions implicated in phonological processing. Despite considerable variation in accuracy for both words and non-words, the majority of participants demonstrated the increased lexicality effects in reading and spelling that are considered the hallmark features of phonological dyslexia and dysgraphia. Increased lexicality effects were also documented in spoken language tasks such as oral repetition, and patients performed poorly on a battery of phonological tests that did not involve an orthographic component. Furthermore, a composite measure of general phonological ability was strongly predictive of both reading and spelling accuracy, and we obtained evidence that the continuum of severity that characterized the written language disorder of our patients was attributable to an underlying continuum of phonological impairment. Although patients demonstrated qualitatively similar deficits across measures of written and spoken language processing, there were quantitative differences in levels of performance reflecting task difficulty effects. Spelling was more severely affected than reading by the reduction in phonological capacity and this differential vulnerability accounted for occasional disparities between patterns of impairment on the two written language tasks. Our findings suggest that phonological dyslexia and dysgraphia in patients with perisylvian lesions are manifestations of a central or modality-independent phonological deficit rather than the result of damage to cognitive components dedicated to reading or spelling. Our results also provide empirical support for shared-components models of written language processing, according to which the same central cognitive systems support both reading and spelling. Lesion-deficit correlations indicated that phonological dyslexia and dysgraphia may be produced by damage to a variety of perisylvian cortical regions, consistent with distributed network models of phonological processing.

Deep dyslexia for kanji and phonological dyslexia for kana: different manifestations from a common source

A Japanese-speaking stroke patient with disrupted phonology but relatively good semantics was severely impaired in nonword reading, with better preserved and imageability-modulated word-reading in both kanji and kana. This basic similarity of reading in the two Japanese scripts was accompanied by the following differences: (i) distinct error patterns (prominent semantic errors for kanji vs. phonological errors for kana); (ii) a more pronounced imageability effect for kanji; and (iii) a remarkable pseudohomophone advantage for kana. The combination of deep dyslexia for kanji and phonological dyslexia for kana in a single patient suggests that these are not two distinct reading disorders.

Phonological dyslexia and phonological impairment: an exception to the rule?

The condition known as phonological dyslexia involves very poor reading of non-words, with otherwise good word reading performance [e.g. Derouesné & Beauvois, 1979; Sartori, G., Barry, C., & Job, R. (1984). Phonological dyslexia: A review. In R. N. Malatesha & H. A. Whitaker (Eds.), Dyslexia: A global issue. The Hague: Martinus Nijhoff Publishers]. Theoretical accounts of this non-word reading impairment suggest disruption to either a component of a non-lexical orthographic-phonological reading route [that is specifically involved in reading non-words; Coltheart, M., Rastle, K., Perry, C., Langdon, R., & Zeigler, J. (2001). A dual route cascaded model of visual word recognition and reading aloud. Psychological Review, 108, 204-256] or to generalised phonological processes on which novel reading is heavily dependent [Farah, M., Stowe, R. M., & Levinson, K. L. (1996). Phonological dyslexia: Loss of a reading-specific component of cognitive architecture? Cognitive Neuropsychology, 13, 849-868; Harm, M. W., & Seidenberg, M. S. (1999). Phonology, reading acquisition, and dyslexia: Insights from connectionist models. Psychological Review, 106, 491-528]. The present paper questions the latter hypothesis: that phonological dyslexia always occurs in connection with some other form of phonologically based disruption (i.e. in a 'cluster' of impairments that are not necessarily reading-specific). Contrary to this view, several recent studies have reported that phonological dyslexia can occur without corresponding generalised phonological impairment [e.g. Caccappolo-van Vliet, E., Miozzo, M., & Stern, Y. (2004a). Phonological dyslexia without phonological impairment? Cognitive Neuropsychology, 21, 820-839; Caccappollo-van Vliet, E., Miozzo, M., & Stern, Y. (2004b). Phonological dyslexia: A test case for reading models. Psychological Science, 15, 583-590]. However, the work is subject to a number of criticisms. The following study examines performance of a phonological dyslexic case (JH) on a variety of phonological based tasks and, unlike many other studies, components of phonological short-term memory. Despite clear impairments in reading non-words, good performance on a variety of phonological tasks makes the possibility of generalised phonologically based disruption unlikely. The view that JH's good phonological skill was dependent on the use of spelling based strategies was also excluded. As a result, JH's pattern of performance provides clear evidence that phonological dyslexia can occur without any generalised phonological impairment.

Specific Reading and Phonological Processing Deficits are Associated with Damage to the Left Frontal Operculum

Functional neuroimaging studies in normal subjects indicate that a region in the left frontal operculum (FO) is more active when subjects read pronounceable nonwords as compared to most word types. Here, we report convergent evidence on this finding using the lesion method. We tested the prediction that subjects with left FO damage would have impaired reading of pronounceable nonwords, but relatively intact reading of most word types. Eleven target subjects with circumscribed left FO lesions, and two comparison groups of either brain-damaged or normal subjects matched to the target subjects for age, sex, handedness, and education, were studied using reading tasks derived from previous neuroimaging work. As predicted, the FO group was significantly less accurate than the comparison groups at reading nonwords. By contrast, the FO subjects showed relatively intact word reading, a pattern consistent with the syndrome of "phonological dyslexia". The FO subjects, however, did exhibit particular difficulty reading low frequency words with inconsistent grapheme-to-phoneme correspondences (e.g., PINT), which parallels the finding from functional imaging studies that reading such items produces more activation in left FO than reading high frequency words and low frequency words with consistent grapheme-to-phoneme correspondences (e.g., JADE) (Fiez et al., 1999). In several follow-up experiments, we found that the FO subjects were also impaired on other phonological tasks that have been associated with left frontal opercular activation in functional neuroimaging studies. The findings converge nicely with extant functional imaging work, and provide further evidence that regions within the left FO are part of a system that makes specific and critical contributions to some of the phonological processes that support reading.