Sandra Manning, Marilyn Evans3
1 Visual Perception
3 Mill View Middle
When reading, children sometimes report fewer symptoms of visual fatigue if the text is coloured by covering the page with a sheet of coloured plastic (an overlay). Tyrrell et al (1995) examined 46 children aged 8-16 in a mainstream school, showing them text coloured by each overlay in a set of seven. Children who reported benefit from an overlay were relatively poor at reading. After 10 minutes continuous reading they showed a deterioration in reading fluency not shown by other children, accompanied by symptoms of visual fatigue. The deterioration and fatigue did not appear when the overlay was used. A set of coloured overlays that samples hues systematically and comprehensively was subsequently developed by Wilkins (1994). The rationale for the design of these so-called ‘Intuitive Overlays’ is that if, indeed, there is a particular colour that can help with reading, the overlays can be combined to find a close approximation to this colour: the set of overlays samples chromaticity systematically and efficiently.
Jeanes et al (1997) used the Intuitive Overlays in several small-scale studies in county primary schools. They presented each of the colours in turn and allowed children to choose the one that best improved the clarity of text. About 50% of children reported beneficial perceptual effects with the chosen overlay. These children were all given the selected overlay to use if they wished to do so, and 3 months later about half the children who were given overlays were still using them, that is, about 20% of the entire sample of normal school children. Again, these children were relatively poor at reading.
Although in the research by Tyrrell et al the effects of overlays on reading fluency were observable only after 10 minutes continuous reading when the child had begun to tire, it has subsequently proved possible to demonstrate the benefits of overlays in a one-minute test, the Rate of Reading Test. The test consists of a passage of text which is read aloud as quickly as possible for one minute. The score is the number of words correctly read. The passage consists of 10 lines each comprising the same 15 common words in a different random order. The words are familiar to poor readers who are therefore prepared to undertake the challenge of reading. The random order ensures that no word can be guessed from the context; each word must be seen to be read. The absence of any meaning has the advantage that children are often unaware of their errors of omission and transposition of words. The text is printed in a small typeface, closely spaced, in order to increase the visual difficulty.
The Rate of Reading Test would appear to provide a sensitive measure of the visual skills involved in reading. The average rate of reading with an overlay compared to that without is greater in the children who will subsequently use an overlay voluntarily in the long-term (Wilkins et al, 1996; Jeanes et al, 1997).
The increase in reading speed with a coloured overlay is unlikely to be due simply to motivation or other placebo effects. Wilkins and Lewis (1999) used the Rate of Reading test and included a placebo control. Reading rate was compared with no overlay, the chosen overlay, a grey overlay and a grey overlay that was identical except that it carried the label ‘scientific prototype’. The children were told that the prototype was new, that it combined all the colours, that they were one of the first children to use it, and that they were expected to do as well as they could. Performance with this grey overlay did not differ from that with the other, although reading with the chosen coloured overlay was superior. Bouldoukian (1995) had earlier used a similar design, with similar results.
In a study reported by Jeanes et al, (1997, Study 6), the Rate of Reading Test was given without an overlay, with a clear (transparent) overlay, with a grey overlay (the Grey overlay from the set of Intuitive Overlays), and with two coloured overlays from the same set: one of the chosen colour and one of a colour complementary to that chosen. The five conditions were presented in random order. With the overlay of the chosen colour the reading rate was superior to that with no overlay, that with a clear overlay and that with a grey overlay. The reading rate with the overlay of complementary colour did not differ significantly from the rate in the other conditions.
In a further study by Wilkins and Lewis (1999) children undertook the Rate of Reading Test with no overlay, an overlay that was reported as having least benefit, a grey overlay, and the chosen overlay. The four conditions were presented in random order. The reading rate increased in the order in which the conditions are listed above, although the only statistical difference was in the performance with the chosen overlay vis a vis the other conditions.
The above studies are consistent in finding (1) that coloured overlays are superior to clear overlays (a placebo control) and to grey overlays that reduce the contrast and luminance by a similar amount; (2) that quite different colours can be beneficial, although (3) the chosen colour appears to give the greatest benefit; (4) a complementary or aversive overlay colour gives relatively little benefit; (5) the rate of reading is unaffected by motivational instructions.
Reliability and consistency
In more recent work (Wilkins et al, in preparation), a year group of children in middle school were examined. First the children were tested as a group and were asked about symptoms of distortion and discomfort when viewing text. All the children were then examined individually with overlays twice within three days in two sessions, using different methods and examiners. The same number of children, 78 (87%) chose a coloured overlay on both individual test sessions. The rate of reading without the overlay on Session 1 was strongly correlated with the rate of reading without the overlay on Session 2, see Figure 2
The improvement in reading fluency due to the overlay was measured as the ratio of reading speed with the overlay divided by that without. Overall there was an 11% improvement in reading fluency with the chosen overlay. The ratio obtained in Session 1 was strongly correlated with that obtained in Session 2, notwithstanding the different overlays chosen, see Figure 3. The correlation was also high when the ratio for the method used by one examiner (used on half the trials in Session 1 and half in Session 2) was compared with the ratio for the method used by the other examiner.
Notwithstanding the differences in assessment method, 47% of children selected the same colour on both occasions and a further 21% chose an overlay of similar colour. The consistency demonstrated by the children was very considerably above that expected on the basis of chance alone.
The percentage improvement in reading rate is shown in Figure 4. As can be seen, the 47% children who chose the same colour consistently on the two testing sessions showed a greater improvement in reading fluency with the colour than those who chose a similar colour, and these children in turn showed a greater improvement in fluency than those 22% who chose a different colour on each occasion.
In a second recent study all the 378 children in a middle
The symptoms reported during the group testing were similar to those reported when the children were examined individually. The 78 children who chose an overlay reported an average of 2.79 symptoms when questioned as a group, whereas the 11 who did not choose an overlay reported only 1.00 on average. 83% of the children who showed an increase in reading rate of 30% or more reported four or more symptoms on the group test, and 63% of those who reported less than 4 symptoms showed an increase in reading rate of less than 30%.
In another study children were asked to read a set of regular and irregular words in order to infer the phonological reading strategy they were using. There was nothing to suggest that the children who used overlays differed from those who did not with respect to any phonological reading strategy.
Prevalence and colour choice
In a third recent study all the children in Year 3 in 12
Table 3 shows the percentage of children who reported various distortions of the page of text. The 135 children who used overlays throughout the school year are shown separately from the 124 who used overlays initially but subsequently ceased to do so. (The 171 who did not report any perceptual benefit from the overlays when first tested were not issued with overlays).
The most frequently chosen colours, rose and aqua, were chosen by less than 10% of the sample of children. Figure 6 is a diagram summarising the frequency with which each colour was chosen. The length of the lines represents the proportion of children choosing each colour, and the angle of the line, the hue. The figure shows the colours provided by single overlays separately from the colours formed by double overlays.
The choices of children who ceased to use their overlays are shown separately from those of the children who continued to use the overlays. There was no statistical difference in the frequencies with which the various colours were chosen by these two groups.
The children who were still using their overlays in the summer term were more likely to be those who in the previous autumn term read faster with their overlays on the Rate of Reading Test.
Thirty three children chose a grey overlay. These children did not show a significant increase in reading rate with the overlay, suggesting that motivation is not a sufficient explanation for the improvement in reading speed with coloured overlays, as also indicated by the studies reviewed above.
Reading ability, reading speed and use of overlays
Standardised Youngs test scores (average 100, standard deviation 15) were available for 427 children. The 133 children who used overlays had an average reading quotient of 98.7, compared with 102.2 for the remaining 294 who did not use overlays or did not choose them. The average reading speed (without overlays) for the children who used overlays was 67.7 words per minute compared with 76.0 for the remaining 119 children tested. Figure 7 shows a scatter plot relating the reading quotient on the Youngs test of reading attainment to the scores on the Rate of Reading Test, both measured before the overlays were issued.
The range of reading speeds shown in Figure 7 is remarkable. Note that there are good readers (reading quotient > 120) who are reading only 40 words per minute and others with similar reading attainment who are reading more than three times as fast. This range is not due to variability in the rate at which a person can read from one time to the next because the Rate of Reading Test has a very high test-retest reliability (Jeanes et al, 1997). Clearly the Rate of Reading scores reflect large and stable individual differences. Some of these differences may be attributable to visual skills given that (1) reading rate can show improvements with coloured overlays and (2) it is difficult to attribute the individual differences to linguistic skill because the differences exist when reading attainment is controlled. The immediate increase in reading rate when overlays are used is consistent with such a viewpoint.
The above studies show consistency with regard to the proportion of children in mainstream education who report beneficial perceptual effects with coloured overlays, who persist in using overlays and who demonstrate improvements in reading fluency both before and after using them. The choice of colour is individual, yet reliable at re-test. No one colour clearly predominates. The chosen overlay gives greater improvements in reading fluency than others of similar colour. If the choice of overlay colour is consistent at re-test, greater benefits in fluency are demonstrable. A simple symptom questionnaire that can be administered to a class of children will correctly identify 83% of those who will demonstrate an improvement in reading fluency of 30% or more with an overlay, but at the cost of falsely identifying 40% of those who will not demonstrate such an improvement.
The present findings and those reviewed above are consistent in pointing to a visual or visuo-perceptual benefit from colour. Indeed, Scheiman et al (1991) have argued that the benefit from colour is a reflection of binocular dysfunction. Evans et al (1996a,b) have investigated binocular vision of individuals who benefit from using coloured lenses. In general the findings are normal in most individuals. There is a tendency for slightly poorer performance on certain clinical tests of vision (near point of accommodation and prism vergences). Performance is rarely abnormal on these tests, however. Benefits are common in children whose binocular vision is quite normal.
There remains the possibility that colour may be affecting accommodation (focussing of the eyes). Evans et al (1996b) studied children who benefited from coloured glasses and noted that the beneficial colour was not such as to reduce any residual refractive error. Simmers et al (1999) measured changes in focussing and found them normal. However, when steady focus had to be maintained they found abnormal fluctuations. These fluctuations were reduced by the prescribed coloured lenses, but also by grey lenses of similar density. These findings are preliminary, but important in that they reliably demonstrate for the first time a physiological abnormality in these children. The abnormality may be a correlate of visual stress, rather than a component of a causal mechanism for the benefits of coloured glasses. Lightstone et al (1999) noted that the colour optimal for use in lenses was not the same as that optimal in overlays, which suggests that any focussing mechanism is unlikely to be a sufficient explanation.
As yet, no retinal deficit has been demonstrated in individuals who benefit from overlays. Deficits of colour vision on clinical tests are no more prevalent than would be expected on the basis of age and gender (Evans et al, 1996a). There are no obvious optometric or orthoptic deficits on clinical testing (Scott et al, in preparation).
Livingstone et al (1991) and Lovegrove et al (1986) have demonstrated that individuals with dyslexia have an impairment of visual function that affects the visibility of changes in the visual world (magnocellular deficit) The impairment has been widely proposed as providing a basis for the benefits from colour partly on the basis of the suppression of the activity of the magnocellular cells in the presence of red light, first noted by Wiesel and Hubel in 1968 and subsequently widely confirmed. This hypothesis is unable to explain the large individual differences in optimal therapeutic colours (demonstrated in these studies and under double-masked conditions by Wilkins et al in 1994.)
Wilkins (1995) has proposed an alternative speculative explanation which draws together aspects of visual stress in epilepsy, migraine and discomfort when reading. The children who benefit from coloured filters are twice as likely to have migraine in the family as those who show no benefit (Maclachlan et al 1993). Individuals with migraine are thought to have a hyperexcitable visual cortex (Aurora and Welch, 1998) and this may explain their susceptibility to photophobia, given that the visual stimuli that provoke photophobia are very similar to those that trigger seizures in patients with photosensitive epilepsy (Wilkins et al 1999). Gratings that can provoke photosensitive seizures interfere with normal perception (Chronicle and Wilkins, 1996), particularly in individuals with migraine (Chronicle et al, 1995; Chronicle and Wilkins, 1991). Depending upon its layout, text can resemble a pattern of stripes with epileptogenic characteristics, and when it does it can provoke distortions similar to those provoked by such stripes (Wilkins and Nimmo-Smith, 1987; Wilkins, 1995).
Changing the colour of a visual stimulus must inevitably alter the distribution of normal neuronal activity within the visual cortex. Zeki (1983a,b) has measured the spectral sensitivity functions of neurons in visual areas V3 and V5, areas that code for space and movement. The functions show large differences between neurons, particularly in the short wavelength end of the visible spectrum. Similar differences are likely to exist for neurons in other visual areas. Perhaps comfortable colours reduce strong excitation in hyperexcitable regions, reducing an inappropriate spread of excitation. Such an explanation is admittedly speculative, but does have the advantage of the predicting the benefits of coloured lenses recently observed in migraine and photosensitive epilepsy (Wilkins et al., 1999).
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