New insight into the brain mechanisms underlying dyslexia

27th Jan 2017

Humans have a type of long-term memory called implicit memory, that responds less to stimuli repeated over time in a process called neural adaptation. Implicit memory uses past experiences to remember things without thinking about them. New research has shown that dyslexics recover faster than non-dyslexics from their responses to stimuli such as sounds and written words, leading to their perception and reading difficulties. 

Previous research had shown that dyslexia can be due to 'poor anchoring', where dyslexics have inefficient integration of information from recent stimuli, collected as implicit memory. This memory forms 'anchors' that provide specific predictions that clarify noisy stimuli. This lead to the current study to find out why this was not the case for dyslexics.

In the study, the team gave 60 people (half of whom were dyslexic) frequency discrimination and oral reading tasks. The frequency discrimination task involved participants comparing two tones in each trial. The researchers found that all participants' responses were affected by implicit memory of previous stimuli. Both groups were affected in similar ways by very recent stimuli, but the dyslexic group was less affected by earlier stimuli.

To confirm the hypothesis that dyslexics have faster decaying implicit memory, the researchers did the same task but increased the length between stimuli. It was found that participants with dyslexia showed a faster decay of implicit memory on both measures and this also affected their oral reading rate. 

Overall, the team concluded that dyslexics' faster recovery from stimuli can account for their longer reading times, as it causes less reliable predications for both simple and complex stimuli.

These findings can pave the way for earlier diagnosis and interventions of the condition. 

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