Event related potentials recorded in normal and dyslexic subjects when reading in and out of context.

Clinical evidence has shown that expectancy or anticipatory reactions influence the ability to read. It is possible that the reading problems shown by dyslexic children could be due to the absence of anticipatory hypotheses when they decode verbal material. Research was therefore carried out into these clinical observations to see if they could be detected on an electrophysiological level using a technique for recording Event Related Potentials (ERPs). In this study, our intention was to observe if there were any differences between a sample population of normal children and one of dyslexic children in the ERPs recorded on the presentation of words both in and out of context. The words recorded during the reading in context were: the word "la" (the feminine article "the" in Spanish), an "intermediate" word and a "final" word in a series of sentences. The first two have a greater anticipatory load than the reading of the final word since this is the word that closes the meaning of the sentence. Furthermore, as a control, the ERPs that were produced when reading isolated words were recorded, a situation that does not require the presence of anticipatory processes. The control group was made up of subjects with adequate school performance and no pathological background, and the experimental group was composed of subjects whose performance on a psychoeducational battery, previously administered to 120 Mexican children, had been found to be two standard deviations below the established norms. Following the 10-20 international system, electrodes were placed in zones F3, Cz, P3, O1 and O2 and referred to both earlobes. Statistical analysis revealed significant differences between groups in the amplitude of the ERP recording in the left occipital zone for all conditions when reading in sentences ("la," "intermediate" and "final"). It is suggested that this cortical zone participates in decoding verbal material and that it is deficient in subjects with reading problems.