This study aimed to examine the effects of colored blue electronic and overlay filters on reading performance and eye movements of children with and without dyslexia during reading. The results showed that children with dyslexia read slower than those without it, but the reading speed of children with dyslexia improved with the blue overlay filter compared to the blue electronic and no filter conditions. Blue filters (electronic and overlay) also reduced and increased the fixation and saccade durations, respectively. The findings partially supported our hypothesis and are discussed below.
Children with dyslexia took much longer to read the texts than children without dyslexia, which aligned with recent studies (7, 8). Although reading speed varies among children with dyslexia, our results showed that they spent more than twice as much time as children without dyslexia. Such a difference in total reading time clearly depicts the struggle experienced by these children, which can impact several daily activities.
An important finding observed in this study was that the overlay blue filter improved the reading performance of children with dyslexia, showing a significant reduction in reading time, partially supporting our hypothesis. These results resemble those from recent studies which showed that a green filter promoted reduction in the total reading time of children with dyslexia (7); other studies have also shown the beneficial effects of overlay filters on reading difficulties (6, 8, 9). Thus, although the use of spectral filters remains controversial, our results shed light on the importance and contribution of overlay filter use in improving reading performance in children with dyslexia.
Our findings also showed that improvement in reading performance was accomplished by reducing the fixation duration. During reading, the fixation period is important for identification, memorization, and comprehension of words, and it is well known that children with dyslexia exhibit oculomotor impairment (15, 16). Reduction in fixation duration was also observed with the use of a green overlay filter (7) and along with our results, the use of spectral filters leads to important and beneficial effects on eye movement patterns related to improvement in reading performance.
However, it is important to note that reduction of fixation duration in this study was observed in both dyslexic and non-dyslexic groups and with both overlay and electronic filter conditions. Despite the differences in fixation duration, no difference in reading performance was observed in the non-dyslexic group. Thus, it seems that the blue filter might have also promoted accommodation of eye movements, with shorter fixation duration not sufficient to impact the task performance (in this case, the total reading time). Such results were expected because colored tints can also promote functional implications for people without reading difficulties, such as dyslexia (17). Moreover, the reading time of children without dyslexia was already much shorter, and differences in eye movement patterns may have been insufficient for reducing this time.
Children with dyslexia showed a higher number of fixations and saccades (Figs. 3a and 4a, respectively), indicating more complex eye movements during reading. Razuk et al. (7) also observed an increased number of pro- and retro-saccades, suggesting that children with dyslexia return to letters and words previously seen, as the content may not be acknowledged by the central nervous system. The results of the present study are in line with these observations, although we did not discriminate between pro- and retro-saccades. However, a higher number of saccades is indicative of children with dyslexia moving their eyes forward and backward more often than children without dyslexia.
Finally, a striking result of this study was the difference in the total reading time observed between the overlay and electronic filter conditions. The reduction in reading time was only significant in the blue overlay filter condition. The use of a colored filter seems to promote alleviation of cortical hyper excitability, as suggested by Wilkins (14), leading to a decrease in the contrast of the visual stimulus and consequently allowing better reading performance. Our results showed that such alleviation occurred only in the overlay filter condition. This suggestion is in line with an fMRI study by Kim et al. (11) showed that in patients with Irlen syndrome, the regions in the left-middle and superior temporal cortices involved in comprehension were significantly activated during reading with a colored blue filter (80% of the participants selected blue filters) compared to reading without a colored filter.
Interestingly, the effect on reading performance was only observed when children with dyslexia read with the blue overlay, but not with the blue electronic filter. Such differences owing to the different filters can be explained by the observed spectrum displayed in Fig. 1. As shown, because the monitor displays colors based on the RGB color model, it is possible to identify the three peak components (Red-580; Green-530; and Blue-450 nm). In the no-filter condition, the intensity in these three components was the highest compared to both filter conditions. Moreover, both the blue overlay and electronic filters significantly reduced the color components at all wavelengths but were more accentuated in the wavelengths of the green and red components. This reduction was expected because the filter was blue, meaning that the blue light remained, but the other light wavelengths attenuated, and the spectra showed such a filtering effect. However, the blue overlay filtering attenuation was more accentuated than that observed for the blue electronic filter. Thus, considering that the colored filter possibly alleviates abnormal excitability of cortical areas (14), the stimulus provided by the blue overlay was less excitable than the electronic filter and, consequently, did not significantly impact reading performance.
Finally, there is a need to further understand not only the impact of colored filters on reading capabilities, but also the possible effects on eye movements. It is well known that children with dyslexia show different oculomotor patterns than children without dyslexia (15, 16), but the effects of colored filters still need to be understood. Moreover, considering the changes in wavelengths due to filter and color manipulations, this is an important matter considering the impact on readers with dyslexia.
Our results clearly reveal the beneficial effects of the blue overlay filter on reading performance in children with dyslexia. Moreover, improvements in reading performance are accomplished by changes in oculomotor patterns, which reduce fixation time. By contrast, the electronic blue filter did not improve reading but still led to changes in eye movement patterns. The observed difference in reading impact between the filters can be explained by the different attenuation provided by them, as the overlay attenuation was larger compared to the electronic filter’s regarding the green and red colors. These findings are promising; however, several issues need to be considered for more defined color changes in the reading capabilities of children with dyslexia.