Differences of dyslexia in each language must be added to this variety of definitions and classifications. Actually, English and Spanish differ in the phonetic and visual aspects of their language structures. For that reason, the proportion of each subtype of dyslexia is different in anglo-saxon countries than in hispanic nations. While in Spanish language there is a great proportion of disorders on visual and spatial decodification, English has a wider proportion of phonetic and secuential trouble. That's because Spanish is a more phonological language than English, and its teaching at school applies an analytic- synthetic methodology.
Several facts cause disparity among discoveries in clinical neurophysiology.
Many of the presented cognitive tests showed some methodological problems, and the studied populations were too heterogenous. Another level of complexity lies on the fact that dynamic neurophysiology involves new technical and methodological problems, not only because face or eyes's movement may contaminate the records, but also the selection of references may cause trouble. Moreover, there may be some difficulties in sampling the cognitive activity, mostly because it's related whether with variations on attention, efforts or frustration towards the task. Finally, two kids who carry the same subtype of dyslexia but have diverse educational levels would answer differently to the same test. The child who has the lowest educational level would add other variations to the activity caused by the reading.