Functional and structural neural contributions to skilled word reading

Reading is an essential skill in our everyday lives and individuals are required to process, understand, and respond to textual information at an increasingly rapid rate in order to be active participants in society. The role of spatial attention in reading has recently been emphasized, whereby better spatial attentional skills are associated with stronger reading skills, and spatial attentional training has a large impact on improving reading ability. However, the neuroanatomical correlates of reading and attention have primarily been studied in isolation. Further, there has recently been a shift to understanding how underlying white matter connectivity networks contribute to cognitive processes. However, much of the research focusing on the intersection of reading and spatial attention, as well as underlying white matter connectivity, has focused primarily on individuals with reading impairments. This thesis will focus on unraveling the neural relationship between spatial attention and reading, and how structural connectivity accounts for functional activation in reading tasks. In Chapter 2, we examine the neural relationship between lexical and sublexical reading with voluntary and reflexive spatial attention. In Experiments 1 and 2, participants performed overt reading of both lexical exception word (EW; words with inconsistent spelling-to-sound correspondences, e.g., ‘pint’) and sublexical pseudohomophone (PH; non-words that when decoded phonetically sound like real words, e.g., ‘pynt’) reading tasks, as well as tasks involving either voluntary attention (Experiment 1) or reflexive attention (Experiment 2) during functional magnetic resonance imaging (fMRI). Experiment 3 used hybrid combined reading attention tasks during fMRI, whereby the spatial attentional cue preceded presentation of the EW or PH stimulus. Overall, the results from these experiments showed that sublexical reading was more strongly associated with brain regions involved in voluntary attention, whereas lexical reading was more strongly associated with brain regions involved in reflexive attention. Thus, Experiments 1, 2 and 3 lend support to the idea that lexical and sublexical reading strategies are differentially associated with these two types of attention. In Chapter 3, we examined the extent to which fine-grained underlying white matter connectivity is able to predict fMRI activation during both lexical reading and phonetic decoding in skilled readers. Experiment 4 employed EW and PH reading and a computational modeling technique to model the relationship between whole-brain structural DTI connectivity and task-based fMRI activation during lexical and sublexical reading. Results from this study showed that brain activation during both lexical and sublexical reading in skilled readers can be accurately predicted using DTI connectivity, specifically in known reading and language areas, as well as important spatial attentional areas. Thus, this research suggests that there is a fine-grained relationship between skilled reading and extrinsic brain connectivity, showing that functional organization of reading and language can be determined (at least in part) by structural connectivity patterns. Together, the studies presented in this thesis provide valuable insight into functional and structural contributions to word reading that may serve as biomarkers of skilled reading, which in turn may have important implications for understanding and remediating reading impairments

The Development of Orthographic Knowledge: A Cognitive Neuroscience Investigation of Reading Skill

This investigation compared the effects of explicit letter-sound training to holistic word training on the development of word recognition in a novel orthography paradigm. In a between-subjects design, participants were trained to read spoken English words printed in the alphabet script of Korean Hangul. Training took place over four separate sessions with assessment measures conducted throughout. Compared to the holistic training, the component training condition resulted in significantly better transfer to novel word forms and retention of previously learned items. Furthermore, compared to component training, holistic training yielded greater sensitivity to frequency. Variability in the holistically trained condition revealed bimodal distribution of performance: a high and low performing subset. Functional MRI measured cortical responses to the training conditions. Imaging results revealed generally greater responses in the "reading network" overall for the explicit component-based training compared to holistic training, in particular, regions of the inferior and superior parietal gyri as well as the left precentral gyrus. In a comparison of readers within the holistic group, we found that readers who implicitly derived the sublexical patterns in the writing system activated more of the reading network than those who did not sufficiently acquire this knowledge. This latter group primarily activated ventral visual regions. We conclude that explicit training of sublexical components leads to optimal word recognition performance in alphabetic writing systems due to the redundant mechanisms of decoding and specific word form knowledge

The role of the left fusiform gyrus in reading: An examination of Chinese character recognition

The left fusiform gyrus is hypothesized to be selectively involved in visual word processing. Nevertheless, the particular components of reading to which this area responds is the subject of much controversy. In Experiment 1, activity in the left fusiform gyrus was measured using functional magnetic resonance imaging (fMRI) while subjects performed a phonological task with regular and irregular Chinese characters. Results exhibited greater activity for irregular than regular characters in the left fusiform gyrus, suggesting that this region is involved in the direct route of the dual-route model. In Experiment 2, activity was measured using fMRI while subjects performed phonological, semantic, and orthographic tasks with irregular Chinese characters. The left fusiform gyrus exhibited greater activity during the orthographic task than during the phonological and semantic tasks, which did not differ, suggesting that this region is involved in orthographic processing to a greater extent than phonological or semantic access

A Dual-Route Approach to Orthographic Processing

In the present theoretical note we examine how different learning constraints, thought to be involved in optimizing the mapping of print to meaning during reading acquisition, might shape the nature of the orthographic code involved in skilled reading. On the one hand, optimization is hypothesized to involve selecting combinations of letters that are the most informative with respect to word identity (diagnosticity constraint), and on the other hand to involve the detection of letter combinations that correspond to pre-existing sublexical phonological and morphological representations (chunking constraint). These two constraints give rise to two different kinds of prelexical orthographic code, a coarse-grained and a fine-grained code, associated with the two routes of a dual-route architecture. Processing along the coarse-grained route optimizes fast access to semantics by using minimal subsets of letters that maximize information with respect to word identity, while coding for approximate within-word letter position independently of letter contiguity. Processing along the fined-grained route, on the other hand, is sensitive to the precise ordering of letters, as well as to position with respect to word beginnings and endings. This enables the chunking of frequently co-occurring contiguous letter combinations that form relevant units for morpho-orthographic processing (prefixes and suffixes) and for the sublexical translation of print to sound (multi-letter graphemes)

Orthographic priming in Braille reading as evidence for task-specific reorganization in the ventral visual cortex of the congenitally blind

The task-specific principle asserts that, following deafness or blindness, the deprived cortex is reorganized in a manner such that the task of a given area is preserved even though its input modality has been switched. Accordingly, tactile reading engages the ventral occipitotemporal cortex (vOT) in the blind in a similar way to regular reading in the sighted. Others, however, show that the vOT of the blind processes spoken sentence structure, which suggests that the task-specific principle might not apply to vOT. The strongest evidence for the vOT's engagement in sighted reading comes from orthographic repetition-suppression studies. Here, congenitally blind adults were tested in an fMRI repetition-suppression paradigm. Results reveal a double dissociation, with tactile orthographic priming in the vOT and auditory priming in general language areas. Reconciling our finding with other evidence, we propose that the vOT in the blind serves multiple functions, one of which, orthographic processing, overlaps with its function in the sighted

Neural Systems for Reading Aloud: A Multiparametric Approach

Reading aloud involves computing the sound of a word from its visual form. This may be accomplished 1) by direct associations between spellings and phonology and 2) by computation from orthography to meaning to phonology. These components have been studied in behavioral experiments examining lexical properties such as word frequency; length in letters or phonemes; spelling–sound consistency; semantic factors such as imageability, measures of orthographic, or phonological complexity; and others. Effects of these lexical properties on specific neural systems, however, are poorly understood, partially because high intercorrelations among lexical factors make it difficult to determine if they have independent effects. We addressed this problem by decorrelating several important lexical properties through careful stimulus selection. Functional magnetic resonance imaging data revealed distributed neural systems for mapping orthography directly to phonology, involving left supramarginal, posterior middle temporal, and fusiform gyri. Distinct from these were areas reflecting semantic processing, including left middle temporal gyrus/inferior-temporal sulcus, bilateral angular gyrus, and precuneus/posterior cingulate. Left inferior frontal regions generally showed increased activation with greater task load, suggesting a more general role in attention, working memory, and executive processes. These data offer the first clear evidence, in a single study, for the separate neural correlates of orthography–phonology mapping and semantic access during reading aloud

A Common Left Occipito-Temporal Dysfunction in Developmental Dyslexia and Acquired Letter-By-Letter Reading?

We used fMRI to examine functional brain abnormalities of German-speaking dyslexics who suffer from slow effortful reading but not from a reading accuracy problem. Similar to acquired cases of letter-by-letter reading, the developmental cases exhibited an abnormal strong effect of length (i.e., number of letters) on response time for words and pseudowords.Corresponding to lesions of left occipito-temporal (OT) regions in acquired cases, we found a dysfunction of this region in our developmental cases who failed to exhibit responsiveness of left OT regions to the length of words and pseudowords. This abnormality in the left OT cortex was accompanied by absent responsiveness to increased sublexical reading demands in phonological inferior frontal gyrus (IFG) regions. Interestingly, there was no abnormality in the left superior temporal cortex which--corresponding to the onological deficit explanation--is considered to be the prime locus of the reading difficulties of developmental dyslexia cases.The present functional imaging results suggest that developmental dyslexia similar to acquired letter-by-letter reading is due to a primary dysfunction of left OT regions

Grey matter reduction in the occipitotemporal cortex in Spanish children with dyslexia: A voxel-based morphometry study

Structural and functional neuroimaging studies have reported brain alterations in occipitotemporal, temporoparietal, and left frontal areas in dyslexic patients. These areas have been linked to reading skill impairments, due to their involvement in word recognition and processing. However, most of the patients in these studies were speakers of languages with a deep orthography. In this study, we used voxel-based morphometry (VBM) to investigate brain differences in grey matter volume associated with a transparent language in a sample of 25 native Spanish participants (13 dyslexic and 12 non-dyslexic children). Results revealed a volume reduction in the left occipitotemporal cortex and right cerebellum in dyslexics. Significantly, the reduction in occipitotemporal areas has been previously linked to reading in transparent languages. Our results support previous studies and are consistent with the idea that reading problems in languages with a shallow orthography are related to the ventral reading network

Cognitive processes and neural correlates of reading in languages with graded levels of orthographic transparency: Spanish, English and Hebrew

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This thesis examined the cognitive processes and neural correlates involved in reading Spanish (a transparent orthography), English (an intermediate orthography) and Hebrew (an opaque orthography) by bilinguals and trilinguals. The main objectives of the five experiments were to: (i) extend previous findings which demonstrated that orthographic transparency influences the degree of reliance on lexical and sublexical processing, and (ii) assess the effects of orthographic transparency and language proficiency on strategies employed for reading in a second and third language. Word/non-word naming tasks undertaken by Spanish-English bilinguals, Hebrew-English bilinguals and English monolinguals, where frequency, length and lexicality were manipulated, showed a predominant reliance on sublexical processing in Spanish, lexical processing in Hebrew, and a balanced interplay in English. Effects of language proficiency were also observed as slower naming and lower accuracy in English as a second language. Concurrently, while showing an efficient adaptation of reading strategy to the level of orthographic transparency of English, Hebrew bilinguals appeared to show stronger reliance on sublexical processing than Spanish bilinguals, suggesting a compensatory mechanism. fMRI experiments showed that reading in all languages was associated with a common network of predominantly left-lateralised cerebral regions. Reading in each language was associated with some preferential activation within regions implicated in lexical and sublexical processing, in keeping with their graded levels of orthographic transparency. Effects of language proficiency were demonstrated as increased activation within medial frontal regions implicated in attentional processes as well as right-lateralised homologous language-processing regions. Furthermore, the patterns of activation seen in Hebrew readers in English strengthened the notion of a compensatory mechanism. Finally, a trilingual experiment replicated findings observed in bilinguals, revealed the acute complexity of reading in Hebrew as an additional language and further strengthened the concept of a compensatory mechanism in English and Spanish. The present findings further contribute to current knowledge on teaching methods, diagnostic tools and therapeutic strategies for developmental and acquired reading disorders

Distinct neural specializations for learning to read words and name objects

Understanding the neural systems that underpin reading acquisition is key if neuroscientific findings are to inform educational practice. We provide a unique window into these systems by teaching 19 adults to read 24 novel words written in unfamiliar letters and to name 24 novel objects while in an MRI scanner. Behavioral performance on trained items was equivalent for the two stimulus types. However, componential letter-sound associations were extracted when learning to read, as shown by correct reading of untrained words, whereas object-name associations were holistic and arbitrary. Activity in bilateral anterior fusiformgyri was greater during object name learning than learning to read, and ROI analyses indicated that left mid-fusiform activity was predictive of success in object name learning but not in learning to read. In contrast, activity in bilateral parietal cortices was predictive of success for both stimulus types but was greater during learning and recall of written word pronunciations relative to object names. We argue that mid-to-anterior fusiform gyri preferentially process whole items and contribute to learning their spoken form associations, processes that are required for skilled reading. In contrast, parietal cortices preferentially process componential visual-verbal mappings, a process that is crucial for early reading development