Chiara Valeria Marinelli

Transcranial direct current stimulation improves word retrieval in healthy and nonfluent aphasic subjects

A number of studies have shown that modulating cortical activity by means of transcranial direct current stimulation (tDCS) affects performances of both healthy and brain-damaged subjects. In this study, we investigated the potential of tDCS to enhance associative verbal learning in 10 healthy individuals and to improve word retrieval deficits in three patients with stroke-induced aphasia. In healthy individuals, tDCS (20 min, 1 mA) was applied over Wernickes area (position CP5 of the International 10–20 EEG System) while they learned 20 new “words” (legal nonwords arbitrarily assigned to 20 different pictures). The healthy subjects participated in a randomized counterbalanced double-blind procedure in which they were subjected to one session of anodic tDCS over left Wernickes area, one sham session over this location and one session of anodic tDCS stimulating the right occipito-parietal area. Each experimental session was performed during a different week (over three consecutive weeks) with 6 days of intersession interval. Over 2 weeks, three aphasic subjects participated in a randomized double-blind experiment involving intensive language training for their anomic difficulties in two tDCS conditions. Each subject participated in five consecutive daily sessions of anodic tDCS (20 min, 1 mA) and sham stimulation over Wernickes area while they performed a picture-naming task. By the end of each week, anodic tDCS had significantly improved their accuracy on the picture-naming task. Both normal subjects and aphasic patients also had shorter naming latencies during anodic tDCS than during sham condition. At two follow-ups (1 and 3 weeks after the end of treatment), performed only in two aphasic subjects, response accuracy and reaction times were still significantly better in the anodic than in the sham condition, suggesting a long-term effect on recovery of their anomic disturbances.

Electrical stimulation over the left inferior frontal gyrus (IFG) determines long-term effects in the recovery of speech apraxia in three chronic aphasics

A number of studies have shown that modulating cortical activity by means of transcranial direct current stimulation (tDCS) affects the performance of both healthy and brain-damaged subjects. In this study, we investigated the potential of tDCS for the recovery of apraxia of speech in 3 patients with stroke-induced aphasia. Over 2 weeks, three aphasic subjects participated in a randomized double-blinded experiment involving intensive language training for their articulatory difficulties in two tDCS conditions. Each subject participated in five consecutive daily sessions of anodic tDCS (20 min, 1 mA) and sham stimulation over the left inferior frontal gyrus (referred to as Brocas area) while they performed a repetition task. By the end of each week, a significant improvement was found in both conditions. However, all three subjects showed greater response accuracy in the anodic than in the sham condition. Moreover, results for transfer of treatment effects, although different across subjects, indicate a generalization of the recovery at the language test. Subjects 2 and 3 showed a significant improvement in oral production tasks, such as word repetition and reading, while Subjects 1 and 2 had an unexpected significant recovery in written naming and word writing under dictation tasks. At three follow-ups (1 week, 1 and 2 months after the end of treatment), response accuracy was still significantly better in the anodic than in sham condition, suggesting a long-term effect on the recovery of their articulatory gestures.

Single or dual orthographic representations for reading and spelling? A study of Italian dyslexic-dysgraphic and normal children

Italian children with surface dyslexia and dysgraphia show defective orthographic lexical processing in both reading and spelling. It is unclear whether this parallelism is due to impairment of separate orthographic input and output lexicons or to a unique defective lexicon. The main aim of the present study was to compare the single- versus dual-lexicon accounts in dyslexic/dysgraphic children (and in normal but younger children). In the first experiment, 9 Italian children with surface dyslexia and dysgraphia judged the orthographic correctness (input lexicon) of their phonologically plausible misspellings (output lexicon) and of phonologically plausible spellings experimentally introduced for words they consistently spelt correctly. The children were generally impaired in recognizing phonologically plausible misspellings. Parallel deficits in reading and spelling also emerged: Children were more impaired in judging items they consistently misspelt and more accurate in judging items they always spelt correctly. In a second experiment, younger normal children with reading/spelling ability similar to that of the dyslexic/dysgraphic children in the first experiment (but younger) were examined. The results confirmed a close parallelism between the orthographic lexical representations used for reading and spelling. Overall, findings support the hypothesis that a single orthographic lexicon is responsible for reading and spelling performance in both dyslexic/dysgraphic and normal (but younger) children.

Is developmental dyslexia modality specific? A visual-auditory comparison of Italian dyslexics

Although developmental dyslexia is often referred to as a cross-modal disturbance, tests of different modalities using the same stimuli are lacking. We compared the performance of 23 children with dyslexia and 42 chronologically matched control readers on reading versus repetition tasks and visual versus auditory lexical decision using the same stimuli. With respect to control readers, children with dyslexia were impaired only on stimuli in the visual modality; they had no deficit on the repetition and auditory lexical decision tasks. By applying the rate-amount model (Faust et al., 1999), we showed that performance of children with dyslexia on visual (but not auditory) tasks was associated with that of control readers by a linear relationship (with a 1.78 slope), suggesting that a global factor accounts for visual (but not auditory) task performance. We conclude that the processing of linguistic stimuli in the visual and auditory modalities is carried out by independent processes and that dyslexic children have a selective deficit in the visual modality.

Line and word bisection in right-brain-damaged patients with left spatial neglect.

Right-brain-damaged patients with left unilateral spatial neglect typically set the mid-point of horizontal lines to the right of the objective center. By contrast, healthy participants exhibit a reversed bias (pseudoneglect). The same effect has been described also when bisecting orthographic strings. In particular, for this latter kind of stimulus, some recent studies have shown that visuo-perceptual characteristics, like stimulus length, may contribute to both the magnitude and the direction bias of the bisection performance (Arduino et al. in Neuropsychologia 48:2140–2146, 2010). Furthermore, word stress was shown to modulate reading performances in both healthy participants, and patients with left spatial neglect and neglect dyslexia (Cubelli and Beschin in Brain Lang 95:319–326, 2005; Rusconi et al. in Neuropsychology 18:135–140, 2004). In Experiment I, 22 right-brain-damaged patients (11 with left visuo-spatial neglect) and 11 matched neurologically unimpaired control participants were asked to set the subjective mid-point of word letter strings, and of lines of comparable length. Most patients exhibited an overall disproportionate rightward bias, sensitive to stimulus length, and similar for words and lines. Importantly, in individual patients, biases differed according to stimulus type (words vs. lines), indicating that at least partly different mechanisms may be involved. In Experiment II, the putative effects on the bisection bias of ortho-phonological information (i.e., word stress endings), arising from the non-neglected right hand side of the stimulus were investigated. The orthographic cue induced a rightward shift of the perceived mid-point in both patients and controls, with short words stressed on the antepenultimate final sequence inducing a smaller rightward deviation with respect to short words stressed on the penultimate final sequence. In conclusion, partly different mechanisms, including both visuo-spatial and lexical factors, may support line and word bisection performance of right-brain-damaged patients with left spatial neglect, and healthy participants.

The effect of morphology on spelling and reading accuracy: a study on Italian children

In opaque orthographies knowledge of morphological information helps in achieving reading and spelling accuracy. In transparent orthographies with regular print-to-sound correspondences, such as Italian, the mappings of orthography onto phonology and phonology onto orthography are in principle sufficient to read and spell most words. The present study aimed to investigate the role of morphology in the reading and spelling accuracy of Italian children as a function of school experience to determine whether morphological facilitation was present in children learning a transparent orthography. The reading and spelling performances of 15 third-grade and 15 fifth-grade typically developing children were analyzed. Children read aloud and spelled both low-frequency words and pseudowords. Low-frequency words were manipulated for the presence of morphological structure (morphemic words vs. non-derived words). Morphemic words could also vary for the frequency (high vs. low) of roots and suffixes. Pseudo-words were made up of either a real root and a real derivational suffix in a combination that does not exist in the Italian language or had no morphological constituents. Results showed that, in Italian, morphological information is a useful resource for both reading and spelling. Typically developing children benefitted from the presence of morphological structure when they read and spelled pseudowords; however, in processing low-frequency words, morphology facilitated reading but not spelling. These findings are discussed in terms of morpho-lexical access and successful cooperation between lexical and sublexical processes in reading and spelling.

Spelling Acquisition in English and Italian: A Cross-Linguistic Study.

We examined the spelling acquisition in children up to late primary school of a consistent orthography (Italian) and an inconsistent orthography (English). The effects of frequency, lexicality, length, and regularity in modulating spelling performance of the two groups were examined. English and Italian children were matched for both chronological age and number of years of schooling. Two-hundred and seven Italian children and 79 English children took part in the study. We found greater accuracy in spelling in Italian than English children: Italian children were very accurate after only 2 years of schooling, while in English children the spelling performance was still poor after 5 years of schooling. Cross-linguistic differences in spelling accuracy proved to be more persistent than the corresponding ones in reading accuracy. Orthographic consistency produced not only quantitative, but also qualitative differences, with larger frequency and regularity effects in English than in Italian children.

Costs and benefits of orthographic inconsistency in reading:evidence from a cross-linguistic comparison

We compared reading acquisition in English and Italian children up to late primary school analyzing RTs and errors as a function of various psycholinguistic variables and changes due to experience. Our results show that reading becomes progressively more reliant on larger processing units with age, but that this is modulated by consistency of the language. In English, an inconsistent orthography, reliance on larger units occurs earlier on and it is demonstrated by faster RTs, a stronger effect of lexical variables and lack of length effect (by fifth grade). However, not all English children are able to master this mode of processing yielding larger inter-individual variability. In Italian, a consistent orthography, reliance on larger units occurs later and it is less pronounced. This is demonstrated by larger length effects which remain significant even in older children and by larger effects of a global factor (related to speed of orthographic decoding) explaining changes of performance across ages. Our results show the importance of considering not only overall performance, but inter-individual variability and variability between conditions when interpreting cross-linguistic differences.

Modeling individual differences in text reading fluency: a different pattern of predictors for typically developing and dyslexic readers

This study was aimed at predicting individual differences in text reading fluency. The basic proposal included two factors, i.e., the ability to decode letter strings (measured by discrete pseudo-word reading) and integration of the various sub-components involved in reading (measured by Rapid Automatized Naming, RAN). Subsequently, a third factor was added to the model, i.e., naming of discrete digits. In order to use homogeneous measures, all contributing variables considered the entire processing of the item, including pronunciation time. The model, which was based on commonality analysis, was applied to data from a group of 43 typically developing readers (11- to 13-year-olds) and a group of 25 chronologically matched dyslexic children. In typically developing readers, both orthographic decoding and integration of reading sub-components contributed significantly to the overall prediction of text reading fluency. The model prediction was higher (from ca. 37 to 52% of the explained variance) when we included the naming of discrete digits variable, which had a suppressive effect on pseudo-word reading. In the dyslexic readers, the variance explained by the two-factor model was high (69%) and did not change when the third factor was added. The lack of a suppression effect was likely due to the prominent individual differences in poor orthographic decoding of the dyslexic children. Analyses on data from both groups of children were replicated by using patches of colors as stimuli (both in the RAN task and in the discrete naming task) obtaining similar results. We conclude that it is possible to predict much of the variance in text-reading fluency using basic processes, such as orthographic decoding and integration of reading sub-components, even without taking into consideration higher-order linguistic factors such as lexical, semantic and contextual abilities. The approach validity of using proximal vs. distal causes to predict reading fluency is discussed.

Does pronounceability modulate the letter string deficit of children with dyslexia? A study with the rate and amount model

The locus of the deficit of children with dyslexia in dealing with strings of letters may be a deficit at a pre-lexical graphemic level or an inability to bind orthographic and phonological information. We evaluate these alternative hypotheses in two experiments by examining the role of stimulus pronounceability in a lexical decision task (LDT) and in a forced-choice letter discrimination task (Reicher–Wheeler paradigm). Seventeen fourth grade children with dyslexia and 24 peer control readers participated to two experiments. In the LDT children were presented with high-, low-frequency words, pronounceable pseudowords (such as DASU) and unpronounceable non-words (such as RNGM) of 4-, 5-, or 6- letters. No sign of group by pronounceability interaction was found when over-additivity was taken into account. Children with dyslexia were impaired when they had to process strings, not only of pronounceable stimuli but also of unpronounceable stimuli, a deficit well accounted for by a single global factor. Complementary results were obtained with the Reicher–Wheeler paradigm: both groups of children gained in accuracy in letter discrimination in the context of pronounceable primes (words and pseudowords) compared to unpronounceable primes (non-words). No global factor was detected in this task which requires the discrimination between a target letter and a competitor but does not involve simultaneous letter string processing. Overall, children with dyslexia show a selective difficulty in simultaneously processing a letter string as a whole, independent of its pronounceability; however, when the task involves isolated letter processing, also these children can make use of the ortho-phono-tactic information derived from a previously seen letter string. This pattern of findings is in keeping with the idea that an impairment in pre-lexical graphemic analysis may be a core deficit in developmental dyslexia.