Some recent studies on dyslexia have suggested a selective abnormality in the magnocellular visual pathway. To verify this hypothesis, we investigated motion-onset visual evoked potentials (VEPs) (predominantly testing the magnocellular system) as well as pattern-reversal VEPs (presumably testing the parvocellular system) in 20 dyslexics and 16 controls (both groups with a mean age of 10.0 years). Although the latencies and amplitudes of the main positive peak of pattern-reversal VEPs did not differ between the dyslexic and control group, the motion specific negative peak of motion-onset VEPs was significantly delayed (p<0.001) in dyslexics. Our results confirm a selective magnocellular pathway disorder in dyslexics and indicate that the motion-onset VEPs might serve as an objective method for early diagnosis of dyslexia.
The purpose was to test parameters of visual evoked potentials (VEPs) and of event-related potentials (ERPs) in deaf subjects to verify visual and cognitive CNS functions in a handicapped group of the population. Three types of visual stimuli (with dominating parvocellular or magnocellular system activation or with cognitive tasks) were used in the study. Six deaf persons (4 women, 2 men, mean age 17 years) and 6 persons with normal hearing (sex- and age-matched) were included in this pilot study. In all types of stimulation, latencies and amplitudes of main VEPs and ERPs components were evaluated. No significant latency differences were found. However, significantly reduced amplitudes were found in the occipital area for responses to motion and cognitive stimuli which might be interpreted as a part of functional reorganization of the extrastriate and cognitive cortical areas of deaf subjects.
The West Bohemia earthquake swarm foci are approximated by a circular seismic source model, which radius is assumed to depend only on magnitude of the event. We consider two different models of average slip (i) a constant slip and (ii) a slip exponentially scaled to the magnitude of the event. Based on these assumptions, we stacked the contributions of individual events into representative final fault slip. We processed in such a way four significant swarms recorded during the last three decades in 1986, 1997, 2000 and 2008. Constant slip model indicates final slip was composed of 2 or 3 principal asperities located on one or two different planes. On the contrary, scaled slip model indicates that one big asperity prevails. It is not possible yet to select the preferred slip model. Analysis of the temporal activity of all swarms generally shows three principal phases: starting phase, main phase and fading phase; the upwards trend of activity spreading was observed (slip animation is presented in www supplement http://www.ig.cas.cz/kolar/StopPhase/Asperity). The maximal possible cumulative slip value may have reached the order of meters., Petr Kolář, Bohuslav Růžek, Alena Boušková and Josef Horálek., and Obsahuje bibliografii