Reading ability and visual perception: evidence from Lexilens glasses

Developmental Dyslexia is a neurodevelopmental disorder that affects about 10% of the population causing impairment to read despite a normal intelligence. Many theories about Developmental Dyslexia have been formulated, from the classical visual deficit view of the disorder to the most influent phonological deficit hypothesis, and the debate is still open. The present study aimed to investigate the placebo and nocebo effect of expectations on reading performance in university students. A pair of polarized and backlit glasses (i. e. Lexilens) were used. They allow visual information to pass through with different speeds when tuned to specific temporal frequencies. These glasses are sold as a compensatory tool for dyslexic people since they have been proven to help them read more effortlessly. The placebo effect was found, along with another interesting effect: poor readers (-1,5 DS on speed and errors reading performance) requested slower temporal frequencies of the flickering glasses in the tuning procedure. This supports the magnocellular theory of dyslexia that links reading difficulties to impairments in the brain's magnocellular pathway, which processes rapid visual and auditory information. Poor readers require low flicker frequencies, which could indicate that, when given the option to choose the speed at which visual information enters the brain, they select a slower rate to have enough time to process it adequately. This supports the hypothesis that dyslexia may be due to a difficulty in processing visual information, so, an impairment in the magnocellular pathway.