And, in the context of disputed findings, perhaps the infamous ‘publication bias’ effect ought to be mentioned. This bias refers to the very human desire to read, and publish, findings rather than non-findings. A large number of studies do not find what others have purported to; they do not support other work. In some cases these studies may be published, but often they are so boring (they may have found absolutely nothing of significance) that they are either not submitted at all or are not published. Editors of journals are human and they operate in a marketplace. They naturally tend to seek the stirringly conclusive rather than the enervatingly inconclusive. It is interesting to publish an article with an exciting new claim - for example perhaps that ‘dyslexia’ is caused by a previously unconsidered influence such as the amount of daylight we experienced in our first year of life. The subsequent research that finds that this isn’t really the case, that there is no relationship between early exposure to sunlight and later literacy ability, is dull reading by contrast. It may never see the light of day, and the original claim will stand, by default, and be referenced in other writings. It may become accepted as ‘truth’, at least for a time. (A. N. Other et al have shown that …) The precise size and nature of this publication bias is not clear, of course, but it exists, may be large (perhaps especially in a field like dyslexia) and considerably affects what we consider to be ‘reality’. We might take less as read if we were able, in fact, to read more. (And a recent study claims that over 50% of studies produce findings which are later found to have been wrong! Oh well …)
To say that this theoretical area - the neurology, or neuropathology, behind dyslexia - is unresolved is an understatement. No theory has reached anything approaching consensus and theories which have been cross-examined through research are frequently not supported, or not strongly supported. Scepticism and patience remain proper attitudes towards all this research.
I once met a lady who wore plain, very pale yellow spectacles when reading. She told me that she was dyslexic and was convinced she could not read any but the simplest of texts without them (they were not lenses but absolutely plain glass). With her spectacles on, she read even academic texts absolutely fluently. She had tried many different colours, all of which helped about equally, she said. She had plumped for yellow simply because she liked yellow. Irlen lenses (which are plain but colour tinted spectacles), or coloured overlays (which are clear but colour tinted plastic sheets) sometimes, as in this case, have instant and stunning effects on the ease of reading. Sometimes the effect is small and sometimes there is no effect at all. (Irlen 1991, Tyrell et al 1995.) A useful, short review of research is Whiteley & Smith (2001). Some writers assert that it is ‘dyslexics’ who are helped by these lenses, or overlays. However, writing in the same volume of the Journal of Research in Reading as Whiteley & Smith, Wilkins et al (2001) report finding that around half of ‘normal’ schoolchildren in their three samples experienced reading as easier, and did it better, through coloured overlays; some individuals improved by over thirty per cent. They found that ‘A substantial proportion of children reported symptoms of visual stress...’ (ibid. p. 50) and it was particularly these children who improved most, and most reliably, when using their preferred colour overlay. Symptoms of ‘visual stress’ included letter movement, text blurring and uncomfortable brightness. Almost a third of those who noticed improvement were still voluntarily using their overlay at the end of the school year, eight months after being introduced to it.
The effect is most gratifying, and when it works, it really works. Nobody knows why it should. Wilkins et al (2001) speculate that as ‘visual stress’ is reportedly more common among migraine and epilepsy sufferers they may all be due to a ‘hyperexciteable visual cortex’. Scotopic sensitivity syndrome (or Meares-Irlen syndrome) is a syndrome of the visual system. It is not specific to literacy though capable, apparently, of dramatically affecting it. For ‘dyslexia’ to have any meaning it must be a syndrome which is specific to literacy - not a syndrome relating to sight in general, for example. The sometime success of Irlen lenses or coloured overlays at alleviating reading difficulty is clearly significant, when it is, but leaves the dyslexia debate approximately where it was before they came along. (Kriss & Evans, 2005, Singleton & Trotter 2005).