Dyslexic individuals have deficits in detecting visual stimuli embedded in high levels of perceptual noise. Here we show that visually symptomatic dyslexics, who otherwise had elevated contrast thresholds for discriminating symbols in visual noise, had thresholds similar to non-dyslexics when wearing colored filters. These findings provide evidence that colored filters, which minimize the visual distortions and discomfort of dyslexics when reading, improve dyslexics&#x27; noise exclusion to normal levels

Nadia Northway

Velitchko Manahilov

William A. Simpson

English

Nature Precedings

1 
 
 
Colored filters improve exclusion of perceptual noise in visually symptomatic 
dyslexics 
 
Nadia Northway1, Velitchko Manahilov1 and William A. Simpson2 
1Department of Vision Sciences, Glasgow Caledonian University, Cowcaddens, 
Glasgow, G4 0BA, UK. 
2 School of Psychology, University of Plymouth, Drake Circus, Plymouth, PL4 
8AA, UK. 
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Dyslexic individuals have deficits in detecting visual stimuli embedded in high 
levels of perceptual noise. Here we show that visually symptomatic dyslexics, 
who otherwise had elevated contrast thresholds for discriminating symbols in 
visual noise, had thresholds similar to non-dyslexics when wearing colored 
filters. These findings provide evidence that colored filters, which minimize the 
visual distortions and discomfort of dyslexics when reading, improve dyslexics’ 
noise exclusion to normal levels. 
 Developmental dyslexia is manifested as a difficulty with reading given 
normal individual intelligence that cannot be explained by other factors such as 
sensory acuity, learning opportunities or brain injuries1. Recently, an influential 
theory 2-4 proposed that the reading difficulties of dyslexics may reflect deficits in 
extracting important sensory information from irrelevant distractors. Dyslexic 
children need higher contrast levels than normal readers for detecting patterns 3 or 
motion coherence4 in the presence of visual noise, but not in the absence of noise. 
Converging evidence shows that children with language learning disabilities5 and 
dyslexia6 also have substantial deficits in speech perception and detection of tonal 
targets only under conditions with auditory noise. 
 Dyslexic readers frequently experience perceptual distortions of shape, 
color, motion and asthenopia (sore, tired eyes, headaches and photophobia) which 
impair their reading abilities7. The symptoms of visual stress7 (also known Meares-
Irlen syndrome8) have not been clearly defined in the literature, but some subjects 
report a sustained reduction of the discomfort and perceptual distortions and show 
improvement of reading speed when using precision tinted lenses.  
 We hypothesized that if a noise-exclusion deficit is an underlying 
characteristic of dyslexia, colored filters may have an effect on the visual 
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performance of visually symptomatic dyslexics in the presence of noise, but not in 
the absence of noise. We measured contrast thresholds for discriminating letter-like 
symbols in the presence and absence of luminance noise using a two-interval forced 
choice procedure (Fig. 1 and Supplementary Methods). Dyslexic and non-dyslexic 
individuals were tested without filters, with colored filters and neutral density filters 
whose transmittances matched those of the colored filters. 
 
Figure 1 about here 
 
 Dyslexics with visual stress syndrome (n=10) had reported visual 
distortions, headaches and discomfort which were reduced by colored filters 
selected by means of the Intuitive Colorimeter9 (Supplementary Methods). They 
had shown an improvement in reading speed of more than 5% when using their 
precision tinted filters10 and had been wearing their colored filters for a minimum of 
4 months. The non-dyslexics (n=10) had no visual abnormality and did not receive 
any benefit from the use of colored filters. 
 The presence of noise elevated significantly (ANOVA, main effect of noise, 
F(1,18)=670, P<0.001, Supplementary Methods) the contrast thresholds (Fig. 2). 
Tukey post hoc comparisons showed that when the stimuli were presented on a 
uniform background (Fig. 2a), there were no significant differences between the 
thresholds of different subject groups. When the stimuli were embedded in noise 
(Fig. 2b), dyslexics had significantly (P<0.005) higher contrast thresholds (8.0%) 
than non-dyslexics (5.3%). With colored filters, however, the differences between 
the dyslexics’ and non-dyslexics’ thresholds were not significant. The use of neutral 
density filters also resulted in significantly (P<0.05) higher contrast thresholds of 
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dyslexics (8.2%) as compared to non-dyslexics (5.8%). Intriguingly, colored filters 
reduced significantly the dyslexics’ contrast thresholds (5.1%) as compared with 
those without filters (8.0%, P=0.001) or with neutral density filters (8.2%, 
P<0.001). The thresholds of non-dyslexics without filters, with colored and with 
neutral density filters were not significantly different.  
 
Figure 2 about here 
 
 This study showed that visually symptomatic dyslexics had noise-exclusion 
deficits when discriminating symbols without filters and with neutral density filters 
but not with colored filters. The ability to exclude noise (distractors) depends on the 
tuning characteristics of the perceptual templates11. At the neuronal level, the tuning 
characteristics of visual neurons are modulated by cortical suppression, for example 
GABA mediated suppression12. Therefore, the non-optimal visual processing in 
dyslexics might be due to reduced cortical suppression4. This impairment of cortical 
suppressive mechanisms might result in hyperexcitability which has been regarded 
as a possible neural mechanism underlying the perception of visual distortions in 
individuals with visual stress syndrome13. 
 How could colored filters modify the noise-exclusion mechanisms of 
dyslexics? The selection of colored filters by means of the Intuitive Colorimeter is 
based on adjustments of saturation and hue of light illuminating a page of text until 
visual distortions and discomfort are minimized9. The reduction of visual distortions 
and discomfort might be based on “emotional attention”14 driven by color. Specific 
colors can elicit specific emotional responses in humans which may have impact on 
mood and performance. Warm colors (red, yellow) have been associated with 
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excitement and stimulation and they improve performance in tasks involving short-
term memory and problem solving15. Cool colors (blue and green) have been related 
to comfort, security and calm. It should be noted that some dyslexics reported that 
the colors selected by the Intuitive Colorimeter were similar to the colors of their 
home environment. Anecdotally, facial tension is seen to reduce in subjects when 
their preferred color is in use, along with subjective reports of increased relaxation.  
 We speculate that the observed effects of colored filters on noise exclusion 
might reflect some improvement of suppressive cortical mechanisms of dyslexics 
due to top-down influences of “emotional attention”. Whatever the mechanisms 
underlying the effects of colored filters are, such filters may improve the ability of 
dyslexics with visual stress syndrome to extract important sensory information from 
irrelevant distractors. 
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References: 
1. Critchley, M. The dyslexic child. (London: Heinemann Medical 1970). 
2. Sperling, A.J., Lu, Z.L. & Manis, F.R. Ann. Dysl. 54, 281-303 (2004). 
3. Sperling, A.J., Lu, Z.L., Manis, F.R. & Seidenberg, M.S. Nat. Neurosci. 8, 
862-863 (2005). 
4. Sperling, A.J. Lu, Z.L., Manis, F.R. & Seidenberg, M.S. Psychol. Sci. 17, 
1047-1053 (2006). 
5. Ziegler, J.C., Pech-Georgel, C., George, F., Alario, F.-X. & Lorenzi, C.  PNAS, 
102, 14110-13115 (2005). 
6. Chait, M., Eden, G., Poeppel, D., Simon, J.Z., Hill, D.F. & Flowers, D.L. Brain 
Lang. 102, 80-90 (2007). 
7. Wilkins, A, Visual Stress. (Oxfords Psychology Series. Oxford Science 
Publications 1995). 
8. Irlen, H. Reading by the Colors. (New York: Avery Publishing Group Inc. 
1991). 
9. Wilkins, A.J., Nimmo-Smith, M.I. & Jansons, J. Ophth. Physiol. Opt. 12, 381-
385 (1992). 
10. Wilkins, A.J. Ophthal. Physiol. Opt. 22, 448-454 (2002). 
11. Lu, Z.L. & Dosher, B.A. Vision Res., 38, 1183-1198 (1998). 
12. Tsumoto, T., Ecksrt, W. & Creutzfeldt, O. Exp Brain Res. 34, 351-363 (1979). 
13. Wilkins, A.J., Huang, J. & Cao, Y. J Res. Read. 27, 152-162 (2004). 
14. Vuilleumier, P. Trends Cogn. Sci. 9, 585-594 (2005). 
15. Knez, I. J Environ. Psych. 21, 201-208 (2001). 
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Figure Captions 
Figure 1. High contrast examples of symbol strings embedded in luminance noise. 
In each trial, subjects were presented with two intervals each of which contained a 
three-symbol string built up by a random selection of symbols resembling “u” and 
“n”. The middle symbols in the first and second intervals were different; the 
flanking symbols in each interval were randomly selected. Subjects judged whether 
the middle symbol “u” was presented in the first or second interval. Contrast 
thresholds were measured by a staircase method in the absence and presence of 2D 
dynamic Gaussian noise whose spectral density was 1.4 µsdeg2 (Supplementary 
Methods). 
 
Figure 2. Contrast thresholds of non-dyslexics (empty markers) and dyslexics (filled 
markers) for discriminating symbols in the absence (a) and presence (b) of 
luminance noise without filters (NoFs), with colored filters (ColFs) and neutral 
density filters (NDFs). Error bars show 95% confidence intervals.   
  
 
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Supplementary Table 1. Reading and cognitive scores (means and s.d.). 
 
 
 
Non dyslexic 
(n=10) 
Dyslexic 
(n=10) 
P 
Age (years) 24(4) 20(7) n.s. 
Rate of reading without filters 
(words per minute) 
112(26) 66(13) <0.01 
Rate of reading with colored 
filters (words per minute) 
106(23) 84(16) <0.01 
Sight Word Reading* 116(14) 85(24) <0.01 
Phonemic decoding* 113(13) 79(19) <0.01 
Non verbal IQ** 114(12) 110(18) n.s. 
Verbal IQ** 115(13) 111(19) n.s. 
* TOWRE Test; **Kaufman Brief Intelligence Test;  
n.s. = non significant.  
 
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Supplementary Table 2. Chromaticity and transmission co-ordinates for the colored 
filters used by the dyslexic and non-dyslexic subjects. Mean transmittance for the 
dyslexic subjects is 39.8%.  
 
Subject x chromaticity y chromaticity Luminous 
Transmittance % 
1 0.204 0.298 23 
2 0.275 0.345 39 
3 0.194 0.373 14 
4 0.269 0.320 48 
5 0.371 0.258 32 
6 0.335 0.408 57 
7 0.324 0.330 41 
8 0.298 0.315 59 
9 0.204 0.254 27 
10 0.279 0.298 58 
Non-dyslexics 0.275 0.345 40 
 
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Supplementary Figure 1. Example of the words used and crowded nature of the rate 
of reading test. 
 
come see the play look up is cat not my and dog for you to 
the cat up dog and is play come you see for not to look my 
you for the and not see my play come is look dog cat to up 
dog to you and play cat up is my not come for the look see 
play come see cat not look dog is my up the for to and you 
to not cat for look is my and up come play you see the dog 
my play see to for you is the look up cat not dog come and 
look to for my come play the dog see you not cat up and is 
up come look for the not dog cat you to see is and my play 
is you dog for not cat my look come and up to play see the 
 
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N a t u r e P r e c e d i n g s : h d l :

Reading by the Colors.

The dyslexic child.

Trends Cogn.

Visual Stress. (Oxfords Psychology Series.

Colored filters improve exclusion of perceptual noise in visually symptomatic dyslexics

http://precedings.nature.com/documents/1729/version/1

Colored filters improve exclusion of perceptual noise in visually symptomatic dyslexics

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