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Poster D25, Thursday, November 9, 6:15 – 7:30 pm, Harborview and Loch Raven Ballrooms

Connections between implicit learning and reading fluency: an fMRI investigation

Ola Ozernov-Palchik1,2, Tracy Centanni2,4, Sara Beach2,3, Sidney May2, Meredith Brown1, John Gabrieli1;1Tufts University, 2Massachusetts Institute of Technology, 3Harvard University, 4Texas Christian University

Developmental dyslexia is a prevalent learning disability affecting approximately 10% of all individuals. It is characterized by difficulties with speed and accuracy of word decoding, reading, and spelling. Functional studies of dyslexia have demonstrated altered response in left-hemispheric temporo-parietal, occipito-temporal, and inferior frontal regions during tasks requiring phonological decoding and single word reading. Few studies to date have examined neural activation during a naturalistic reading task and the brain basis of reading fluency in dyslexia is not well understood. Fluent reading relies on perceptual learning of the distributional statistics of phonology and orthography of one’s language, and on automatic integration across multiple components of the reading network. Since both perceptual learning and skill automatization operate under implicit learning conditions, fluency deficits in dyslexia have been hypothesized to stem from underlying impairments in implicit learning. No studies to date, however, have examined the association between implicit learning skills and the neural components of reading fluency in dyslexia. The current study investigates the neural underpinnings of reading fluency in adults with and without dyslexia and relates them to out-of-scanner performance on a range of implicit learning tasks. Participants are asked to read seven paragraphs out loud in their normal reading voice and rate in a 3T-scanner. Each paragraph appears on the screen for 16 seconds, followed by a control block with arrows pointing up and down, requiring the participant to describe the orientation of arrows (“up” or “down”). This is followed by fixation. Participants also completed several implicit learning tasks outside the scanner. 1) In rotary pursuit, participants attempt to maintain contact between a hand-held stylus and a light moving rapidly around the circumference of a figure. With practice, participants increase the time per trial that they are able to maintain contact with the light. 2) In mirror tracing, participants trace a figure with a stylus, only seeing their hand, the stylus, and the figure reflected in a mirror. With practice, participants trace the figure more quickly and tend to make fewer departures from the figure. 3) In selective adaptation, participants must identify ambiguous phonemes on a /b/-/d/ continuum, after exposure to several prototypical instances of either of these phonemes. Participants also complete behavioral measures of reading accuracy and fluency. Preliminary results suggest activation in distinct occipito-temporal and inferior frontal regions of the reading network during the in-scanner fluency task (p<0.05, uncorrected). The examination of differences in response patterns between typical readers and individuals with dyslexia reveals the neural mechanisms of reading fluency in dyslexia. Relations between implicit learning and reading fluency will be discussed and theories of an implicit learning deficit as an etiological mechanism in dyslexia will be evaluated.

Topic Area: Language Disorders

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