Dyslexic Adults Can Learn from Repeated Stimulus Presentation but Have Difficulties in Excluding External Noise

We examined whether the characteristic impairments of dyslexia are due to a deficit in excluding external noise or a deficit in taking advantage of repeated stimulus presentation. We compared non-impaired adults and adults with poor reading performance on a visual letter detection task that varied two aspects: the presence or absence of background visual noise, and a small or large stimulus set. There was no interaction between group and stimulus set size, indicating that the poor readers took advantage of repeated stimulus presentation as well as the non-impaired readers. The poor readers had higher thresholds than non-impaired readers in the presence of high external noise, but not in the absence of external noise. The results support the hypothesis that an external noise exclusion deficit, not a perceptual anchoring deficit, impairs reading for adults

Motion deficits in dyslexia are restricted to high external noise displays

Studies of motion perception in dyslexia have usually used random dot kinetograms with high external noise. Is the reported motion deficit in dyslexia due to deficiencies in motion perception per se, or due to deficiencies in excluding noise in the displays? In this study, we compared the motion perception thresholds of both dyslexic and nondyslexic children, and dyslexic and non-dyslexic adults using first-order coherent motion displays that varied in noise level and signal salience. Both dyslexic children and adults had higher motion thresholds than non-dyslexic children and adults when the task involved first-order motion processing in high noise. Dyslexics performed as well as non-dyslexics, however, when the signal was clearly separated from the noise or noise was reduced. Thus dyslexics appear to have normal motion perception, but have difficulty processing motion in high external noise. The ability to exclude noise or ignore distractors while focusing on the what is relevant may play a role the creation of appropriately flexible yet solid phonological and orthographic categories, a fundamental process in learning to read

Language Deficits in Dyslexic Children: Speech Perception, Phonology and Morphology

5> Developmental dyslexia is diagnosed in children who fail to acquire age-appropriate reading skills in the absence of other cognitive dysfunctions, such as poor vision, or frank neurological deficit (Stanovich, 1988; Vellutino, 1979). Dyslexic children typically exhibit difficulties in recognizing printed words, and consequently perform poorly on such tasks as nonsense word reading, spelling, and reading comprehension (Lyon, 1995; Rack, Snowling, Bell, & Hughes, 1992). Dyslexia is sometimes thought to be an impairment that is This research was supported by NICHD grant HD 29891-03 and NIMH grant 04756. Marc Joanisse was supported by NSERC (Canada) postgraduate award 208931. Mark Seidenberg was supported by a Research Scientist Development Award, NIMH KO201188. We are grateful to Richard Wright for assisting in developing the speech stimuli, and to Michael Harm and Maryellen MacDonald for helpful discussions. We thank the students, teachers and principals of Buffum, Burcham, C

Examples of stimuli used in the four experimental conditions of the letter detection task.

<p>a.) Without noise, small stimulus set size; b.) Without noise, large stimulus set size; c.) Noise, small stimulus set size; d.) Noise, large stimulus set size.</p

The mean contrast threshold values by group for a) each experimental condition and b) for the trials with and without noise.

<p>Error bars represent s.e.m.</p

Performance on the test battery by group.

<p><i>Note</i>. Values in the table are based on standardized scores, except for Nelson Denny Comp. (stanines; max: 9), Exception Words (raw score; max: 70), GORT Passage Score (standard score; max for this age range: 16), and Phoneme Elision (standard score; max for this age range: 12).</p

Neuroanatomical precursors of dyslexia identified from pre-reading through to age 11

Developmental dyslexia is a common reading disorder that negatively impacts an individual's ability to achieve literacy. Although the brain network involved in reading and its dysfunction in dyslexia has been well studied, it is unknown whether dyslexia is caused by structural abnormalities in the reading network itself or in the lower-level networks that provide input to the reading network. In this study, we acquired structural magnetic resonance imaging scans longitudinally from 27 Norwegian children from before formal literacy training began until after dyslexia was diagnosed. Thus, we were able to determine that the primary neuroanatomical abnormalities that precede dyslexia are not in the reading network itself, but rather in lower-level areas responsible for auditory and visual processing and core executive functions. Abnormalities in the reading network itself were only observed at age 11, after children had learned how to read. The findings suggest that abnormalities in the reading network are the consequence of having different reading experiences, rather than dyslexia per se, whereas the neuroanatomical precursors are predominantly in primary sensory cortices