reading speed and colour
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reading speed and colour
Some people experience distortions when they look at striped patterns, provided the stripes have certain characteristics. The characteristics are those of strong patterns — patterns that can be seen most easily, that interfere with the perception of other stimuli most readily, that evoke the greatest electrical or blood-flow changes in the brain, and that can provoke headaches or even seizures in those who are susceptible. Text provides a strong striped pattern. The distortions of text may involve blurring, movement of letters, words doubling, shadowy lines, shapes or colours on the page, and flickering. The distortions are at their most confusing in small, closely spaced printed text, but they also occur to a lesser extent in handwriting. The distortions are characteristic of a condition that some have called Meares–Irlen syndrome and others visual stress. The cause of the distortions is not known with any certainty. Some authors have hypothesized that the distortions are due to a dysfunction, perhaps a hyperexcitability, of nerve cells in the visual cortex of the brain. Individuals with migraine are particularly susceptible to the distortions in strong patterns, and there is other evidence that in migraine the cortex can be hyperexcitable.
The perceptual distortions may occur quite independently of any refractive error, although they are often, but not invariably, associated with a mild binocular vision difficulty. The binocular difficulties do not appear to be the basis for the distortions, and indeed the reverse may in fact be the case: the distortions may interfere with binocular control.
A substantial proportion of children in mainstream primary education (perhaps as many as 20 per cent) will report distortions of text. It is difficult to elicit reports of these subjective phenomena without bias, but children who report distortions differ from others in that they read faster and for longer without discomfort when the text is coloured, either by covering the page with a coloured sheet of plastic (an overlay) or when coloured glasses (spectral filters) are worn. The children report that the colour reduces the distortions. Children with reading difficulty are slightly more likely than others to report distortion, and to benefit from coloured overlays. The susceptibility to distortions runs in families. The children who benefit from colour are twice as likely to have migraine in the family as those who do not.
Each individual benefits from a different colour, and the precision of colour required to optimize reading speed is remarkable. Departures from optimum of two just-noticeable differences are sufficient to reduce reading speed appreciably. The possible long-term effects of wearing coloured glasses for reading are unknown at present. It seems that children benefit most from colour if treatment is offered as soon as any reading difficulty is suspected, before the cycle of failure has begun. Many 7-year-olds use coloured overlays for a year or two and then discard them as unnecessary. This is usually because reading fluency without the overlay has improved.
The British College of Optometrists recommends that children use and demonstrate benefit from a coloured overlay before treatment with coloured glasses is considered. The therapeutic colour in glasses is not the same as that in overlays. When you use an overlay only part of the visual scene is coloured and the eyes are adapted to white light. When you wear glasses the entire visual scene is coloured and the eyes are adapted to the coloured light. (Usually you are quite unaware of this adaptation. For example, the colour of light from a normal household light bulb is very yellow in comparison to daylight, but you are rarely aware of this.) The neurological processes involved when the entire scene is coloured are very different from those when only part of the scene is coloured. The optimal colour of a pair of lenses can be assessed only under conditions in which a sufficiently large range of colours is assessed while the eyes are fully adapted to each colour in turn.
The distortions may be less pronounced when reading becomes fluent and text ceases to be a meaningless collection of confusing shapes. Although some people seem to grow out of the distortions, many do not. Visuoperceptual distortion still remains undetected in many children, and many enter adulthood without ever having been treated.
(Published 2004)
The perceptual distortions may occur quite independently of any refractive error, although they are often, but not invariably, associated with a mild binocular vision difficulty. The binocular difficulties do not appear to be the basis for the distortions, and indeed the reverse may in fact be the case: the distortions may interfere with binocular control.
A substantial proportion of children in mainstream primary education (perhaps as many as 20 per cent) will report distortions of text. It is difficult to elicit reports of these subjective phenomena without bias, but children who report distortions differ from others in that they read faster and for longer without discomfort when the text is coloured, either by covering the page with a coloured sheet of plastic (an overlay) or when coloured glasses (spectral filters) are worn. The children report that the colour reduces the distortions. Children with reading difficulty are slightly more likely than others to report distortion, and to benefit from coloured overlays. The susceptibility to distortions runs in families. The children who benefit from colour are twice as likely to have migraine in the family as those who do not.
Each individual benefits from a different colour, and the precision of colour required to optimize reading speed is remarkable. Departures from optimum of two just-noticeable differences are sufficient to reduce reading speed appreciably. The possible long-term effects of wearing coloured glasses for reading are unknown at present. It seems that children benefit most from colour if treatment is offered as soon as any reading difficulty is suspected, before the cycle of failure has begun. Many 7-year-olds use coloured overlays for a year or two and then discard them as unnecessary. This is usually because reading fluency without the overlay has improved.
The British College of Optometrists recommends that children use and demonstrate benefit from a coloured overlay before treatment with coloured glasses is considered. The therapeutic colour in glasses is not the same as that in overlays. When you use an overlay only part of the visual scene is coloured and the eyes are adapted to white light. When you wear glasses the entire visual scene is coloured and the eyes are adapted to the coloured light. (Usually you are quite unaware of this adaptation. For example, the colour of light from a normal household light bulb is very yellow in comparison to daylight, but you are rarely aware of this.) The neurological processes involved when the entire scene is coloured are very different from those when only part of the scene is coloured. The optimal colour of a pair of lenses can be assessed only under conditions in which a sufficiently large range of colours is assessed while the eyes are fully adapted to each colour in turn.
The distortions may be less pronounced when reading becomes fluent and text ceases to be a meaningless collection of confusing shapes. Although some people seem to grow out of the distortions, many do not. Visuoperceptual distortion still remains undetected in many children, and many enter adulthood without ever having been treated.
(Published 2004)
— Arnold J. Wilkins
- Bibliography
- Wilkins, A. (2002). 'Coloured overlays and their effects on reading speed: a review'. Ophthalmic and Physiological Optics, 22.
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Oxford Companion to the Mind
The Oxford Companion to the Mind. Second Edition. Copyright © Oxford University Press, 2004. All rights reserved.
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