There is much discussion about the relationships between dyslexia and visual processing. Some countries don’t test for visual processing issues at all when testing for dyslexia, while many countries report that assessments are used which measure visual processing in some way. Visual-spatial skills are taken into account when testing for dyslexia in Sweden, while Spanish assessors look for visual scanning, and visual perception is accounted for in Croatia, and to some extent the United Kingdom.
Yet debate remains hot, not only about whether visual perception is a key element of dyslexia, but about what „visual perception“ actually means in these instances. Some studies have indicated that visual perception deficits may play an important role in both dyslexia and dyscalculia, while others have reported visual perception deficits as less important, even irrelevant factors. This appears to reflect the differences in what those studies are looking for. But where studies report strong correlation between dyslexia and visual processing deficits, such visual components cannot be ignored as potentiallyi forming a strong component of dyslexia.
What „Visual Perception“ in Dyslexia (almost certainly) Isn’t
In some dyslexia tests, assessors have been reported as asking subjects to read through coloured filters. This indicates strongly that they are looking for a condition called Meares-Irlen Syndrome (sometimes simply: Irlen Syndrome). While Irlen syndrome is itself a subject of some controversy, it would be at most a visual processing disorder commonly confused with dyslexia, with somewhere between a third and a half of dyslexics reporting having it.
Other clinical studies report that the relationship between dyslexia and visual processing issues is far from clear. To assess the direct contribution of visual factors to the slower and less accurate reading abilities of dyslexic subjects, one such study formulated a task that was similar in many respects to single word reading in its basic visual characteristics, but had none of the other phonological, morphological, or semantic aspects of reading. It was concluded that there was no correlation to speak of between visual processing difficulties and reading. However, this was mainly looking for „optical visual“ deficits, rather than a „visual processing“ deficits.
What „Visual Perception“ in Dyslexia (probably) Is
Many studies (see for instance Valdois, Fischer, Cheng, and others) broadly identify two major candidates for visual perception difficulties in dyslexic subjects: poor letter-string recognition and processing, and problems with spatial processing.
Regarding the deficit in letter-string processing, research suggests this reflects a visual processing disorder compatible with other reported elements of dyslexia, such as working memory issues and visual attention span disorder (i.e., a deficit in the number of distinct visual elements that can be processed, in parallel, in a multi-element arrangement). It manifests mainly in the recognition and processing of letter position (including place and orientation) within a series of letters. Subjects may experience difficulties in identifying where a letter is, which it is, or „which way round“ it is (such as confusing „b“ and „d“) within a letter string.
Regarding the spatial processing aspect of visual perception, this concerns, among other things, a subject’s capacity to detect fast changes in small visual patterns and pattern orientation, or coherently moving dots on a screen. Dyslexic subjects as a whole tend to perform significantly below the level of non-dyslexic subjects in activities testing for this. Other facets of deficient spatial processing may include a difficulty in speed and place discrimination, but also, interestingly, the detection, discrimination, and manipulation of letter-strings. For example, determining which letter comes next in a sequence; which letter is missing from a sequence; which geometric shape is a rotation of one of choice of options; or which figure completes a logical sequence, may be typical of such a skill.
Select the correct answer figure which will continue the series
Taken from Non-Verbal Series Practice Questions: Questions & Listed Answers (toppr.com)