Lu said there is a "lot of evidence" of learning problems from ambient noise. In one such study, Manis and a collaborator from UCLA found that children with dyslexia struggled to discriminate similar sounds, like "spy" and "sky," because they weighed irrelevant differences in sounds equally with key distinctions.
Manis also cited research from Finland and the United States showing that infants with dyslexic parents lag behind their peers in forming categories for speech sounds.
In the conclusion to their study in Psychological Science, the authors speculate that the deficit in noise exclusion may have biochemical roots in abnormal levels of GABA, a neurotransmitter that helps the brain to filter out irrelevant information.
"This may become interesting for drug development," said Lu, who is testing this hypothesis with functional magnetic resonance imaging trials.
Lu and his collaborators interpret the new results as a rejection of the "magnocellular hypothesis" - named for a type of neuron involved in processing fast visual information - that influenced dyslexia research for decades.
The researchers found that the magnocellular pathway works normally both in children with dyslexia and in adult poor readers - as long as visual or aural noise is low.
As external noise goes up, the same subjects begin to score poorly on visual pattern tests.
The deficit persists even when the task requires only slow processing.
"The findings, and particularly the [slow processing] ones, are consistent with the hypothesis that ... dyslexic children have difficulty setting their signal filters to optimum and ignoring distracting noise," Lu said at the time of the Nature Neuroscience study.
The new study in Psychological Science was designed to replicate visual tests on motio
Source:University of Southern California