Dyslexia is a learning disorder that manifests itself as a difficulty with reading, spelling and in some cases mathematics. It is separate and distinct from reading difficulties resulting from other causes, such as a non-neurological deficiency with vision or hearing, or from poor or inadequate reading instruction. It is estimated that dyslexia affects between 5% and 12% of the U.S. population in some degree and is thought to be the result of a neurological defect/difference, and though not an intellectual disability, a language disability, among others. It is also worth noting that most dyslexics who have Boder's Dysiedetic type, have attentional and spatial difficulties which interfere with the reading acquisition process as well.
Visuospatial Cognition and Theories of Developmental Dyslexia:
When we look at a scene we feel that we perceive the visual world in all its detail and richness. This experienced quality and effortlessness of vision masks the fact that scene perception is actually a highly complex cognitive process, which requires the explorative scanning by eye movements, the quick and accurate direction of attention, the anticipation of the consequences of actions, and the integration and comparison of current visual input with stored representations of previously viewed parts of the scene and knowledge of objects and their relationships. A number of striking visual illusions demonstrate that scene perception is in fact a rather fragile process that essentially builds upon assumptions about the visual world to optimally piece together observations from a number of fields of scientific study.
The leading theories on the topic of developmental dyslexia should not be viewed as competing, but instead be seen as a complementary set of theories trying to explain the underlying causes of a similar set of symptoms but from a variety of research perspectives and backgrounds.
Here is a great link for information on the history and theories of developmental dyslexia.
One such theory that has gained note in the past decade is represented by the automaticity/cerebellar theory of dyslexia. Here the biological claim is that the cerebellum of people with dyslexia is mildly dysfunctional and that a number of cognitive difficulties ensue from this dysfunction.
For many years, developmental dyslexia was thought to be a problem related to language itself. However, with the arrival of neuroimaging tools and greater research into the relationship between dyslexia and balance, among other things, opinions began to shift. It has become clear to researchers that developmental dyslexia and the cerebellum are somehow related due to the function of the cerebellum matching the deficits in function associated with developmental dyslexia.
The cerebellum, more than many other areas of the brain, is engaged in processing and deciphering a constant series of "behind the scenes" events. It is forever multitasking in the background of our conscious mind. It is responsible for the sequencing of input, the automatization of tasks and skills, as well as the production and interpretation of verbal and written language. Since developmental dyslexia is defined by problems in these three exact areas, the hypothesis that the cerebellum was responsible, especially when coupled with revelatory neuroimaging studies, has gathered strength and wide acceptance as a promising area of study.
The cerebellum plays a critical role in overall brain function but has particular importance in reading and writing tasks. “Impairments of the cerebellum cause deficits in motor control such as posture and balance, and additional difficulties in achieving ‘automaticity’ of other learned skills” including skills that are related to reading and writing. The complicated issue is deciding where and how there is a “misfire” among neural pathways—a task that can be almost impossible without the use of sophisticated imaging equipment over a long span.
While these problems seem difficult to overcome and detection of the exact location of the impairment may never be known, this does not mean there are not options for those with developmental dyslexia. In fact, cerebellar dysfunction as a theory does not imply a sentence for those with developmental dyslexia to a life of failed reading attempts. With concentrated effort on refining the neural pathways in the cerebellum, along with the sensory connections from the cerebellum to the other critical informational processing centers in the brain, the brain’s natural plasticity can be taken advantage of to establish better neuro-processing to help overcome developmental dyslexia as well as other processing-based learning difficulties.
Nothing about the brain is static. It is always on, always at work; sending, receiving, responding, interpreting. Accordingly, it is always handling input, although this input or the pathways it travels on may not be “optimized” for adequate processing. Neurological issues like these underlie learning challenges and indicate that specific disabilities like developmental dyslexia may be addressed simply… with vestibular-based brain training exercises like those available in the Learning Breakthrough Program.
Rochelle, K., & Talcott, J. (2006). Impaired balance in developmental dyslexia? A meta-analysis of the contending evidence. Journal of Child Psychology & Psychiatry, 47(11), 1159-1166.
Cyril R Pernet, Jean Baptiste Poline, Jean Francois Demonet and Guillaume A Rousselet: BMC Neuroscience (in press) – Brain classification reveals the right cerebellum as the best biomarker of dyslexia. http://www.biomedcentral.com/bmcneurosci/