60 research outputs found

    The VWFA: It\u27s not just for words anymore

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    Reading is an important but phylogenetically new skill. While neuroimaging studies have identified brain regions used in reading, it is unclear to what extent these regions become specialized for use predominantly in reading vs. other tasks. Over the past several years, our group has published three studies addressing this question, particularly focusing on whether the putative visual word form area (VWFA) is used predominantly in reading, or whether it is used more generally in a number of tasks. Our three studies utilize a range of neuroimaging techniques, including task based fMRI experiments, a seed based resting state functional connectivity (RSFC) experiment, and a network based RSFC experiment. Overall, our studies indicate that the VWFA is not used specifically or even predominantly for reading. Rather the VWFA is a general use region that has processing properties making it particularly useful for reading, though it continues to be used in any task that requires its general processing properties. Our network based RSFC analysis extends this finding to other regions typically thought to be used predominantly for reading. Here, we review these findings and describe how the three studies complement each other. Then, we argue that conceptualizing the VWFA as a brain region with specific processing characteristics rather than a brain region devoted to a specific stimulus class, allows us to better explain the activity seen in this region during a variety of tasks. Having this type of conceptualization not only provides a better understanding of the VWFA but also provides a framework for understanding other brain regions, as it affords an explanation of function that is in keeping with the long history of studying the brain in terms of the type of information processing performed (Posner, 1978)

    Ventral occipito-temporal cortex function and anatomical connectivity in reading

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    Previous functional neuroimaging studies of reading in skilled readers, acquired dyslexia and developmental dyslexia have all shown that the left ventral occipito-temporal cortex (vOT) is involved in visual word recognition. Specifically, a region in the left posterior occipito-temporal sulcus lateral to fusiform gyrus and medial to inferior temporal gyrus has been reported to play an important role. However, the precise functional contribution of this area in reading is yet to be fully explored. In this thesis, I empirically evaluated a claim that vOT responds not only to bottom-up processing demands of the visual stimuli but is also influenced by automatic, top-down non-visual processing demands, as proposed by the Interactive Account of vOT functioning. The first part of this thesis investigated the functional properties of vOT during reading, using functional magnetic resonance imaging. In the first project, the top-down influences on vOT were investigated, teasing apart visual and non-visual properties of written stimuli. In the second project, using the Japanese orthography I disentangled a word’s lexical frequency from the frequency of its visual form – an important distinction for understanding the neural information processing in regions engaged by reading and further explored the interactive nature of the vOT responses. The second part then investigated the anatomical basis of these functional interactions between vOT and other cortical regions. I used diffusion-weighted magnetic resonance imaging and tractography, the only method currently available to identify and measure white matter fibre pathways non-invasively and in vivo. My research has demonstrated that vOT integrates bottom-up visual information and top-down predictions from regions encoding non-visual attributes of the stimulus in an interactive fashion. It also illustrated the putative anatomical basis for functional connectivity during reading, which is consistent with the parallel cortical visual pathways seen in other primates. Altogether, the results provide strong support for the Interactive Account

    Typical and Dyslexic Development in Learning to Read Chinese

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    Early and Sustained Supramarginal Gyrus Contributions to Phonological Processing

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    Reading is a difficult task that, at a minimum, requires recognizing a visual stimulus and linking it with its corresponding sound and meaning. Neurologically, this involves an anatomically distributed set of brain regions cooperating to solve the problem. It has been hypothesized that the supramarginal gyrus (SMG) contributes preferentially to phonological aspects of word processing and thus plays an important role in visual word recognition. Here, we used chronometric transcranial magnetic stimulation (TMS) to investigate the functional specificity and timing of SMG involvement in reading visually presented words. Participants performed tasks designed to focus on either the phonological, semantic, or visual aspects of written words while double pulses of TMS (delivered 40 ms apart) were used to temporarily interfere with neural information processing in the left SMG at five different time windows. Stimulation at 80/120, 120/160, and 160/200 ms post-stimulus onset significantly slowed subjects’ reaction times in the phonological task. This inhibitory effect was specific to the phonological condition, with no effect of TMS in the semantic or visual tasks, consistent with claims that SMG contributes preferentially to phonological aspects of word processing. The fact that the effect began within 80–120 ms of the onset of the stimulus and continued for approximately 100 ms, indicates that phonological processing initiates early and is sustained over time. These findings are consistent with accounts of visual word recognition that posit parallel activation of orthographic, phonological, and semantic information that interact over time to settle into a distributed, but stable, representation of a word

    Processing deficits for familiar and novel faces in patients with left posterior fusiform lesions

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    Pure alexia (PA) arises fromdamage to the left posterior fusiformgyrus (pFG) and the striking reading disorder that defines this condition has meant that such patients are often cited as evidence for the specialisation of this regiontoprocessing of writtenwords.There is,however, an alternative view that suggests this region is devoted to processing of high acuity foveal input, which is particularly salient for complex visual stimuli like letter strings. Previous reports have highlighted disrupted processing of non-linguistic visual stimuli after damage to the left pFG, both for familiar and unfamiliar objects and also for novel faces. This study explored the nature of face processing deficits in patients with left pFG damage. Identification of famous faces was found to be compromised in both expressive and receptive tasks. Discrimination of novel faces was also impaired, particularly for those that varied in terms of second-order spacing information, and this deficit was most apparent for the patients with the more severe reading deficits. Interestingly, discrimination of faces that varied in terms of feature identity was considerably better in these patients and it was performance in this condition that was related to the size of the length effects shown in reading. This finding complements functional imaging studies showing left pFG activation for faces varying only in spacing and frontal activation for faces varying only on features. These results suggest that the sequential part-based processing strategy that promotes the length effect inthe reading of these patients also allows themto discriminate between faces on the basis of feature identity, but processing of second-order configural information is most compromised due to their left pFG lesion. This study supports a view in which the left pFG is specialised for processing of high acuity foveal visual information that supports processing of both words and faces.variou

    Visual and auditory vocabulary acquisition in learning Chinese as a second language : the impact of modality-specific working memory training

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    The global aim of this thesis was to investigate underlying working memory processes and neural correlates of visual and auditory vocabulary acquisition in Chinese. As an additional question and pre-condition for examining the main goal I questioned whether visual working memory can be trained separately from auditory and whether intra-modal can be distinguished from across-modal training effects in visual working memory on the behavioral and on the neural level. The Working Memory Training Study was designed to test whether visual working memory processes can be trained specifically on the behavioral and neural level and whether those effects can be separated from across-modal training effect. Decidedly larger training gains after visual working memory training compared with auditory or no training on a visual 2-back task were found. These effects were accompanied by specific training-related decreases in the right middle frontal gyrus arising from visual training only. Likewise, visual and auditory training led to decreased activations in the superior portion of the right middle frontal gyrus and the right posterior parietal lobule. I infer that the combination of effects resulted from increased neural efficiency of intra-modal (visual) processes on the one hand and of across-modal (general control) processes on the other hand. Therefore, visual processes of working memory can be trained specifically, and these effects can be functionally dissociated from alterations in general control processes common to both working memory trainings. These results offered a good starting point to use the training paradigm in the Language Training Study. As exemplified for the visual modality, the working memory training paradigm was successful in training a modality-specific process. Thus, the paradigm was applicable to investigate different transfer effects of visual and auditory working memory training on visual and auditory vocabulary learning in Chinese. The Language Training Study aimed at investigating whether visual working memory training exerts unique influence on learning Chinese visual words (orthographic learning) due to the greater complexity of the Chinese writing system, and, conversely, whether auditory working memory training has a specific impact on learning Chinese auditory words (phonological learning). In addition, training induced modulations in language-related brain networks were examined using fMRI in a pretest-training-posttest design. Both working memory trainings led to positive transfer effects on orthographic learning as compared to no training, whereas for phonological learning no transfer effects were obtained. Differential activation changes after visual and auditory working memory training were found in areas engaged in visual and auditory word processing: Activation sustained/decreased after intra-modal (visual) training in the left mid-fusiform gyrus in the orthographic task. Similarly, activation decreased after intra-modal (auditory) training in the anterior insula in the phonological task. These findings are consistent with the view that working memory training in the equivalent modality enhances the efficiency of perceptual encoding in the orthographic task and incorporating novel sound patterns into long-term phonological representations in the phonological task. Surprisingly, activation increases after across-modal training emerged in both tasks within the same brain regions: Activation increased after auditory training in the mid-fusiform gyrus in the orthographic task and likewise after visual training in the anterior insula in the phonological task, suggesting that working memory training in the complementary modality reflects selective attention to the respective tasks presumably guided by modality-unspecific improvements in executive components of working memory. Moreover, visual training led to additional recruitment of brain regions in the orthographic task, i.e. the right precuneus, presumably mirroring the generation of a mental visual image of the to-be-retrieved character.Das Ziel dieser Arbeit war es zugrundeliegende Arbeitsgedächtnisprozesse und neuronale Korrelate visuellen und auditiven Vokabellernens im Chinesischen zu untersuchen. Als zusätzliche Fragestellung und Voraussetzung um der Hauptforschungsfrage nachzugehen wurde außerdem untersucht, ob visuelles Arbeitsgedächtnis separat von auditivem trainiert werden kann und ob intra-modale von cross-modalen Trainingseffekten auf der Verhaltens- und der neuralen Ebene unterschieden werden können. In der Arbeitsgedächtnistrainingsstudie wurde getestet, ob visuelle Arbeitsgedächtnisprozesse auf der Verhaltens- und der neuronalen Ebene spezifisch trainiert werden und ob solche Effekte von cross-modalen Trainingseffekten separiert werden können. In einer visuellen 2-back Aufgabe zeigten sich deutlich größere Leistungszuwächse nach visuellem im Vergleich zu auditivem oder keine Training. Diese Effekte gingen mit spezifischen trainingsinduzierten Aktivierungsreduktionen im rechten Gyrus frontalis medius einher, die nur auf das visuelle Training zurückgingen. In gleicher Weise führten visuelles und auditives Training zu Aktivierungsreduktionen im superioren Teil des rechten Gyrus frontalis medius und im rechten superioren Parietallappen. Ich schließe daraus, dass die Kombination dieser Effekte durch erhöhte neuronale Effizienz intra-modaler (visueller) Prozesse einerseits und cross-modaler (genereller Kontroll-) Prozesse andererseits zustande kamen. Folglich scheinen visuelle Arbeitsgedächtnisprozesse spezifisch trainierbar zu sein und können funktionell von Veränderungen in generellen Kontrollprozessen, die beide Arbeitsgedächtnistraining gleichermaßen zeigten, dissoziiert werden. Diese Ergebnisse waren einen gute Ausgangsbasis, um das Trainingsparadigma in der Sprachtrainingsstudie anzuwenden. Wie für die visuelle Modalität exemplarisch dargestellt, konnte mit dem Arbeitsgedächtnisparadigma erfolgreich ein modalitäts-spezifischer Prozess trainiert werden. Demnach war das Paradigma geeignet um unterschiedliche Transfereffekte des visuellen und auditiven Arbeitsgedächtnistrainings auf visuelles und auditives Vokabellernen im Chinesischen zu untersuchen. Mit der Sprachtrainingsstudie sollte untersucht werden, ob visuelles Arbeitsgedächtnistraining spezifisch das Lernen chinesischer visueller Wörter (orthographisches Lernen) aufgrund der hohen Komplexität des chinesischen Schriftsystems beeinflusst und in umgekehrter Weise, ob auditives Arbeitsgedächtnistraining spezifisch das Lernen chinesischer auditiver Wörter (phonologisches Lernen) verbessert. Darüber hinaus wurden trainingsinduzierte Aktivierungsveränderungen in sprachrelevanten Gehirnnetzwerken mittels funktioneller Magnetresonanztomographie in einem Pretest-Training-Posttest-Design untersucht. Beide Arbeitsgedächtnistrainings führten zu positiven Transfereffekten beim orthographischen Lernen im Vergleich zu keinem Arbeitsgedächtnistraining, während für phonologisches Lernen keine Transfereffekte gefunden wurden. Unterschiedliche Aktivierungsveränderungen nach visuellem und auditivem Arbeitsgedächtnistraining wurden in Arealen gefunden, die auch bei visueller und auditiver Wortverarbeitung rekrutiert werden: Die Aktivierung wurde nach intra-modalem (visuellem) Training in der orthographischen Aufgabe im linken Gyrus fusiformis aufrechterhalten bzw. fiel ab. In ähnlicher Weise fiel die Aktivierung nach intra-modalem (auditiven) Training in der phonologischen Aufgabe in der linken anterioren Insel ab. Diese Ergebnisse weisen darauf hin, dass Arbeitsgedächtnistraining in der äquivalenten Modalität die Effizienz perzeptuellen Enkodieren in der orthographischen Aufgabe und die Einspeicherung neuer Klangmuster in Langzeitgedächtnisrepräsentation in der phonologischen Aufgabe verstärkt hat. Überraschenderweise wurden Aktivierungserhöhungen nach cross-modalem Training innerhalb derselben Gehirnregionen gefunden: Die Aktivierung im Gyrus fusiformis nahm nach auditivem Training in der orthographischen Aufgabe zu genauso wie die Aktivierung in der anterioren Insel nach visuellem Training in der phonologischen Aufgabe. Dies weist darauf hin, dass Arbeitsgedächtnistraining in der komplementären Modalität zu selektiver Aufmerksamkeitsallokation auf die entsprechende Aufgabe führt, was vermutlich auf modalitätsunspezifische Verbesserungen in exekutiven Arbeitsgedächtnisprozessen zurückzuführen ist. Darüber hinaus führte visuelles Arbeitsgedächtnistraining zu einer zusätzlichen Rekrutierung von Hirnarealen in der orthographischen Aufgabe, dem rechten Precuneus, was wahrscheinlich die Generierung eines visuellen mentalen Bildes des abzurufenden Schriftzeichens widerspiegelt

    "Radical" Thinking about Character Perception: Specifying Pre-lexical and Sub-lexical Processes of Chinese Reading

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    Previous research has examined cross-linguistic importance of phonological and morphological awareness in Chinese and English word recognition, yet few studies have focused on the earlier, pre-lexical aspects of character recognition and evaluated why orthographic awareness is central to Chinese literacy development. Comparing spread of lexical activation between orthographic, phonologic and semantic stores in English and Chinese reading have helped to specify the lexical pathways underlying character decoding and reading comprehension as part of word recognition. The visual orthographic complexity and coarse form-form mappings of the logographic character system, considered in conjunction with the observations of the Lexical Constituency Model and other reading research, suggests that Chinese pre-lexical processing is exclusively orthographic and threshold-based. Sub-character radicals are decomposed sub-lexical (but not “pre-lexical”) representations and are utilized in unfamiliar reading (based on radical frequency and regularity, and other factors). Radical parts are only accessed after orthographic lexical representations are already assembled, meaning their access involves top-down morpho-orthographic decomposition. The first study proposal uses two character recognition training tasks to examine the pre-lexical decoding mechanism that results in perceptual assembly of lexical orthographic representations. Beginning with the basic premise that the semantic cues provided by radical parts also contribute to reading of unfamiliar graphic forms, two follow-up proposals compare the relevance of visual, orthographic and semantic salience of radical components to both real and pseudocharacter recall. It is anticipated that graphic and semantic salience of radicals will have independent and additive effects on recall of unfamiliar forms and both may be able to be incorporated into L2 pedagogies

    Fixing fluency: Neurocognitive assessment of a dysfluent reading intervention

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    The ability to read is essential to attain society’s literacy demands. Unfortunately, a significant percentage of the population experiences major difficulties in mastering reading and spelling skills. Individuals diagnosed with developmental dyslexia are at severe risk for adverse academic, economic, and psychosocial consequences, thus requiring clinical intervention. To date, there is no effective remediation for the lack of reading fluency, which remains as the most persistent symptom in dyslexia. This thesis aims at identifying factors involved in the failure to develop a functional reading network as well as factors of treatment success in addressing the notorious ‘fluency barrier’ in dyslexia. The present work combines a theoretical framework of dyslexia based on the multisensory integration deficit with recent advances in our knowledge of the brain networks specialized for reading. This thesis uses a longitudinal design including both behavioral and neurophysiological measures in dyslexics at 3rd grade of school. Between measurements, we provide an intervention aimed at improving reading fluency by training automation of letter-speech sound mappings. The studies presented in this thesis contribute to our understanding of dyslexics’ deficits and their remediation

    Change blindness: eradication of gestalt strategies

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    Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task
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