The Neurobiological Development of Reading Fluency DOI: http://dx.doi.org/10.5772/intechopen.82806

where significant differences in FA existed between dyslexic and typical readers, and research that used VBA to locate cortical coordinates where FA significantly correlated with reading ability or performance on a reading-based task. Their results were extraordinary. The analysis of 47 foci from 5 experiments (99 subjects), where FA was significantly greater in typical compared to dyslexic readers, and the analysis of 17 foci from 2 experiments (52 subjects), where FA was significantly greater in dyslexic compared to typical readers, yielded no significant clusters when using FDR correction of 0.05. Further, the analysis of 42 foci from 9 experiments (500 subjects), where reading ability was significantly positively correlated with FA, and the analysis of 2 foci from 2 experiments (40 subjects), where reading ability was significantly negatively correlated with FA, also yielded no significant clusters when using FDR correction of 0.05. Studies of children and adults were analyzed separately. No significant clusters were produced when typical readers had significantly higher FA than dyslexic readers or when dyslexic readers had significantly greater FA than typical readers, regardless of age [90]. The fact that these results showed no systematic differences in fractional anisotropy between dyslexic and typical readers, or as a function of reading ability, after correcting for multiple comparisons, underscores the ambiguity inherent in brain research in spite

Neurodevelopment and Neurodevelopmental Disorder

of, or perhaps because of, cutting edge technologies. Hoppenbrouwers,

fore inadequately controlling for spurious findings [93].

worldwide have advanced the discussion in many useful ways.

10. Conclusion

108

Vandermosten, and Boets noted that despite appearing consistent, each one of the studies they included in their meta-analysis produced coordinates at different locations within the temporo-parietal region and corpus callosum [91]. In fact many studies have also reported differences and correlations in a range of other regions distributed widely throughout the cortex [59, 92]. Turkeltaub et al. pointed out that the software commonly used for these kinds of analysis, GingerALE 2.0.4, has since been updated too correct initial errors which made ALE analysis to lenient, there-

There is little doubt that neurobiological investigation into the brain activations of struggling readers is messy and incomplete and fraught with misinformation. Reviews of international studies reveal many areas of agreement regarding the factors that result in dyslexia, but the characteristics of different languages and their orthographies introduce differences in the required processing skills. This is also seen in the unequal application of the Psycholinguistic Grain Size Theory, where transparent languages with a regular orthography are less affected than those opaque languages with many irregular words and derivatives. The contribution of RAN to understanding the neurobiological features of dyslexia appears to have global implications as this naming speed deficit has been found to be more common than even the phonological deficit in both regular and irregular orthographies. These methods and techniques used to investigate the manifestations of dyslexia

Phonological processing and speed have long been in the forefront of international dyslexia research. Particularly in transparent orthographies, phonological impairments have supported the idea of lexical and sub-lexical routes of decoding that utilize different areas in the brain. Difficulties with phoneme blending often precede and contribute to a slower rate of reading. These processing weaknesses eventually produce students who display the dreaded Double Deficit- a condition that in many languages has been identified as the most severely incapacitating. However, in some languages, RAN is useful as a predictor of reading accuracy only

in the early grades. Receptive vocabulary, often an important factor in less

consistent orthographies, has been found to play a role in reading accuracy in more regular orthographies as readers become more experienced, but this seems to rely on specific language features that promote decoding based on lexical aspects of known, related words. So in languages where these language-specific patterns are prevalent, most dyslexics achieve high levels of reading accuracy but remain deficit in reading speed.

Research into the visual processing of struggling readers has focused mainly on the functions of the occipito-temporal reading circuit. Dysfunction in a variety of visuo-attentional skills such as visual search, visual recognition, and visual information processing has been documented in several languages, with both transparent and opaque orthographies. Interesting work in languages that use diacritical vowel markings which are absent after instruction emphasizes the theory that when grapheme-phoneme processing skills are weak, students are unable to develop strong connections in the orthographic lexicon to support further autonomous word recognition. In this case, the results also highlight the importance of visual accuracy and memory for the missing vowel markings. Generally, however, functional imaging studies reveal reduced reading related activation in a left ventral occipitotemporal brain area, often associated as an interface between visual orthographic codes and phonology and meaning. There is some assurance of parity for even complex visual languages like Urdu that RAN continues to be a reliable predictor of reading accuracy. Regardless, the question of effective interventions remains largely unanswered.

American researchers have addressed the problems inherent in dyslexia through new conceptualizations of fluency and definitions that acknowledge the crucial role played by the automatization of underlying subskills at the letter, letterpattern, and word levels. They challenged the validity of the commonly held discrepancy definition of dyslexia which mandates that a student with reading difficulties can be labeled "dyslexic" only if they have an average or higher IQ. Research showed that there were no reliable differences in the brain functioning of poor readers with high IQs and poor readers with low IQs. The effects of instructional intervention have also been explored in studies with American students. Most of this research focuses on explicit instruction in the alphabetic principle and phonological processing. These efforts generally resulted in increases in the activation of left posterior superior temporal gyrus (STG), although processing speed remained unaffected. However, a novel study using visual hemisphere-specific stimulation has shown some advancement in the speed of processing of dyslexic readers. Matching struggling readers to either a left or right hemisphere intervention program by specific oral reading behaviors appears to be helpful in applying an effective remediation program. The differences in the composition of the intervention programs (the left hemisphere lessons are all phonologically decodable words and the right hemisphere lessons are all phonologically decodable non-words) apparently interact with the weak brain processing systems efficiently. The forced pressure of faster and faster recall appears to strengthen the pathways resulting in automatized recall. Brain activations of subjects who achieved levels of automatic processing (recall within 100–250 ms) revealed expected changes: pre-intervention, there was a great deal of diffuse activation in the frontal areas and in the right hemisphere, and post-intervention activation was much more focused bilaterally around the STG and postcentral gyrus with very little activation in the VWFA. Further these documented processing changes were discovered to directly support increases in reading speed in those students reaching automatic levels of visual processing. So, visual hemisphere-specific stimulation has emerged as an intervention tool that influences access to the VWFA in American dyslexic readers.

Other technologies also shed light on the functional connectivity of brain regions important to fluent reading, but, as always, must be scrutinized for reliability. It is well established that diffusion tensor imaging (DTI) and fractional anisotropy are useful tools for understanding the structural integrity of white matter. Many studies have investigated relationships between differences in FA and various reading abilities, and differences in FA in dyslexic and normal readers. Generally these studies identify left hemisphere under-activation from dorsal inferior parietal to ventral occipito-temporal regions and to the middle temporal and the inferior frontal under-activation, with over-activation in left hemisphere anterior insula, primary motor cortex, lingual gyrus, caudate nuclei, thalamus, and right hemisphere medial frontal cortex. However, many researchers have also commented that in spite of apparent consistency, there is substantial disparity in the coordinates locating specific activations in the temporo-parietal region and corpus callosum. These observations led to a careful, but controversial meta-analysis using voxelbased analysis (VBA) to identify cortical coordinates where significant differences in FA existed. These analyses found no systematic differences in FA between dyslexic and typical readers, or as a function of reading ability, and highlighted possible weaknesses in older versions of the software commonly used to make DTI analyses. Clearly, one must engage in this kind of research and rely on these results cautiously.

identification of orthographic units, their transformation into an internal sound and articulation. This program's creators included the appearance of letters and words at an accelerating rate on the screen (although without hemisphere consideration) in an effort to improve automatized naming and visual recognition more effectively than flashcards [95]. The direct comparison of traditional instructional techniques to outcomes produced through a computer-based intervention underscores the power of these types of programs and their impact on the automatization of lexical and sub-lexical reading processes. Perhaps the power of technology in new applications will ultimately provide solutions for the long-suffering dyslexic readers, espe-

cially those of opaque orthographies.

The Neurobiological Development of Reading Fluency DOI: http://dx.doi.org/10.5772/intechopen.82806

Author details

Bobbie Jean Koen

111

University of Houston, Houston, Texas, United States

\*Address all correspondence to: bjkoen@comcast.net

provided the original work is properly cited.

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

For many years, the only neurobiological research was done in adults, which did not allow investigation of the developing brain. Granted, it is very challenging to obtain reliable fMRI results with children, but new techniques and a more permissive environment are encouraging, and the promise of bringing new understandings to fruition as effective intervention practices continues to beckon. Instructional intervention that is designed to improve time-sensitive procedural rather than timefree declarative knowledge of grapheme-phoneme correspondences may overcome the temporal deficit in children by decreasing the over-connectivity of brain regions in the executive panel of working memory- that is the left and right inferior frontal gyrus, and increasing the connectivity between the left inferior frontal gyrus and the middle frontal gyrus (working memory) [94]. From a clinical or educational perspective, remediation seems most targeted and effective when it addresses an isolated disability [71]. The challenge in developing strong intervention tools is to make them engaging, accessible, and fun.

Saine et al. conducted a longitudinal intervention study designed to build a model of predictive values of reading fluency using three different instructional techniques to identify the most effective type of intervention for children with different profiles of core pre-reading skills. Their results show that a computerized remedial reading intervention called GraphoGame was the most successful in remediating reading fluency in Finnish children (7 years old) with deficits in letter knowledge, phonological awareness, and rapid automatized naming [95]. Perhaps reflecting its extremely shallow orthography, (there is full symmetric consistency between graphemes and phonemes and the simplest syllabic structure in the Finnish language) and the fairly long duration of intervention (66 hours), increases in fluency were found in both of the other treatments (remedial reading instruction and mainstream instruction) as well, with the least amount of growth shown in the mainstream group. However, evaluation of data by pre-reading profiles shows that all of the tested profile-types responded most strongly in the computerized reading program.

The GraphoGame program is similar to FlashWord in the structure of the phonological analysis, proceeding from early reading competencies to higher-level concepts, and in the forced, fast processing at the word-level. It was developed to affect the cognitive operations that constitute word reading: the visual
