The Location and Effects of Visual Hemisphere-specific Stimulation on Fluency in Children with the Characteristics of Dyslexia

Fluency is often used as an indicator of reading proficiency, but many students with reading disabilities are unable to benefit from typical classroom interventions. Lorusso, et al. (2006) used a modified FlashWord computer program that tachistoscopically presents words in the right or left visual hemi-field (Visual Hemisphere-specific Stimulation or VHSS). They matched the intervention to the specific reading profiles (dyslexia subtypes) of reading disabled Italian students using parameters proposed by Bakker, Bouma, and Gardien, (1990). After 1440 minutes of intervention, their behavioral results show significant gains in fluency, reading accuracy, spelling, and memory. The present study is designed to replicate Lorusso’s work in English and locate through fMRI imaging the processing areas involved in fluency and changes as a result of the FlashWord intervention. Recent advancements in the conceptualization of fluency (Katzir et al., 2006), define fluency as the automatization of reading processes which results from the automatization of underlying lexical and sublexical skills. This suggests that investigations of the development fluent reading should focus on the fast processing of phonological analysis, as well as underlying skills already linked by fMRI results to specific brain regions. Shaywitz, et al., (2004) focused on three Regions of Interest (ROI) within the core sub-systems supporting the processing of written language in normal readers: the left hemisphere (LH) superior temporal gyrus (STG) in the inferior parietal lobule within the temporoparietal system associated with semantic encoding or word meaning; the posterior aspect of the inferior frontal gyrus (IFG) within the anterior system associated with phonological encoding and sound/symbol associations; and the LH inferior occipito-temporal/fusiform area (VWFA) within the ventral system associated with orthographic encoding and quick recall of high frequency words. It is hypothesized that achieving fluency in reading will involve automaticity within each of these ROIs and that the intervention will increase fluency scores in students with reading disabilities.
This study involved 15 students aged 8-19 years with reading disabilities randomly assigned to Intervention (N = 9) and Delayed Intervention (N = 6) groups. Based on initial fluency assessments, these subjects were matched to a computerized VHSS intervention, FlashWord, modified, targeting either the right or left hemisphere, or both. The Intervention group completed 1440 minutes of their assigned program, and the Delayed Intervention group participated in regular fluency instruction in their classrooms only during the course of the study. Both groups also contributed fMRI data collected during scans conducted pre- and post-intervention and post-intervention assessments of fluency. Analysis of intervention data showed that six of the nine Intervention group subjects (67%) achieved levels of automatic processing (<100 ms as defined by Bakker, et al., 1990) in either left or right visual hemi-field processing. All six of these students (100%) also increased their reading accuracy and rate by an average of 20 wpm. Analysis of fMRI activation maps and ROIs clustered within the core subsystems identified by Shaywitz, et al. (2004), document processing changes in left IFG, left posterior STG, and VWFA that could result from the increase in reading speed. However, statistical comparisons of activation levels in these features were not found to be significant. Analysis of time courses of activation from ROI’s within core reading subsystems are also inconclusive regarding the temporal elements of fluency in neurological processing of written language. Discussion includes analysis of orthographical characteristics of different languages and their impact on this study and the importance of automatization in VWFA. Limitations and future directions are explored.