| Developmental dyslexia is hypothesized to be complex and to diffusely affect the visual system and its related attention system. Thirteen dyslexics and fifteen normal controls underwent electrophysiological and reaction time data collection. Subjects received visual stimulation with colored words producing selective inhibition. Stimuli generated negative priming, attention switching, and Stroop effects. Analysis was done to determine whether dyslexics were impaired in selective suppression in comparison to controls, thus differing from controls in negative priming, switching, and in Stroop interference. Frequency domain averaging and division into 9 bands covering a range from 0 to 40 Hz was completed on electrophysiological data.;Predicted results failed to reach statistical significance. However, younger dyslexics showed the predicted effect of faster reaction times for both the Stroop condition and the negative priming condition in comparison to the identity condition relative to younger controls. Further analysis suggested that approximately 2--3 times more younger subjects would be needed to achieve statistical significance.;Age, condition, their interaction, and their interaction with group all proved statistically significant. Also, the 3-way interaction of age x condition x group proved statistically significant for response accuracy. Older dyslexics were not less accurate in the switching condition vs. the average of the other 3 conditions; however, the other groups experienced a 7--13% decrement in accuracy for the switching condition. The effect of gender was statistically significant, with females producing more errors than males.;Predicted electrophysiological results did not achieve statistical significance. Nonetheless, the data suggest a trend in the predicted direction of increased delta, beta, gamma, and decreased alpha. The most prominent difference occurred as an increase in power in mid and high beta and gamma in the frontal areas for dyslexics in contrast to controls. This activity occurred in the identity, negative priming, and switching conditions. This finding is consistent with fMRI studies showing relative overactivation of anterior areas and underactivation of posterior areas. Lack of left frontal activity in Stroop is consistent with other research implicating anterior cingulate. Control subjects failed to produce the left frontal activity in the corresponding frequency bands for any of the conditions. |
