Green filters appear to increase reading speed for children with dyslexia, according to a new study by Brazilian and French researchers who published their findings in the journal Research in Developmental Disabilities.
The researchers suggest the filters may help reduce visual stimuli available for central nervous system processing, thereby increasing reading speed. The filters show no effect on non-dyslexic children.
“However, studies of their efficacy were methodologically flawed. We used a highly rigorous methodology for the first time,” said first author Milena Razuk, who recently completed her Ph.D. at Cruzeiro do Sul University (São Paulo, Brazil).
The filters are not widely used in Brazil due to a lack of research, but they have been adopted in some countries, such as France. Razuk performed the experiment while in France on a research internship at Paris Diderot University, with support from the Sao Paulo Research Foundation — FAPESP.
The researchers recruited 36 children (ages 9 and 10) — 18 with dyslexia and 18 without dyslexia — to participate in the study at Robert Debré Hospital in Paris. The researchers decided to use just yellow and green filters.
“Twelve colors are available, but we chose two because a very long test would be too demanding for the volunteers,” said José Angelo Barela, a professor at São Paulo State University’s Rio Claro Bioscience Institute (IBRC-UNESP) in Brazil and principal investigator for the project.
The young participants were asked to read passages from children’s books suited to their reading age. The texts were displayed on a computer screen with a yellow filter, a green filter and no filter.
Their eye movements were followed with the Mobile EyeBrain Tracker, a French eye-tracking device certified for medical purposes, consisting of goggles fitted with cameras that record the movements of each eye independently via infrared light signals.
“A child with dyslexia has to fix his or her gaze on the words for a longer time to understand a text. Reading speed is slower as a result,” Barela said.
The filters did not affect reading speed for non-dyslexic children, but the eye-tracking device detected a statistically significant difference for children with dyslexia, who read fastest with the green filter, fixing their gaze on groups of words for 500 thousandths of a second, compared with 600 thousandths of a second using the yellow filter or no filter. The fixation period with or without filters was 400 thousandths of a second for non-dyslexic children.
The authors emphasize that the study did not evaluate whether the use of a green filter improved comprehension of what was read and that further research is needed to explore this area.
The causes of dyslexia are still unclear. Extensive testing has shown that neither impaired eyesight nor intellectual deficiency is part of the condition. In fact, IQ must be normal or above average for dyslexia to be diagnosed.
In addition to reading difficulties, other deficits are often associated with the disorder, including impaired sensorimotor integration.
“It’s as if some source of noise disturbs the brain’s communication with the rest of the body,” Razuk said.
The authors say the green filter may improve reading time due to changes in the visual stimuli available for central nervous system processing.
Previous research has shown that colored filters may reduce cortical hyperexcitability in the brain, which may be greater in dyslexic people, thereby diminishing contrasts in visual stimuli and hence improving reading performance.
Source: Sao Paulo Research Foundation