Magnetic brain activity evoked and induced by visually presented words andnonverbal stimuli

Evoked and induced magnetic brain activity measured over the left hemispher e were tested for their specificity to language-related processing. Induced activity refers to oscillatory alterations time locked but not phase locke d to the stimulus. Welds, false font stimuli, and two types of nonverbal pa tterns were presented visually while subjects performed a nonlinguistic vis ual feature detection task. The comparison of evoked and induced brain acti vity around 200 ms after stimulus onset revealed differential sensitivity t o the stimuli. The M180 component of the evoked magnetic field was larger a t the processing of words and false font stimuli compared with nonverbal st imuli. The induced magnetic brain activity in the 60-Hz band at a compatibl e latency range was col-related with the familiarity of the visual Gestalt. Sensitivity to language-specific information processing can be concluded i f a parameter differentiates condition from the nonlexical conditions. Such a difference was observed at sensors located over the frontal-temporal sca lp regions for induced but not evoked magnetic brain activity. Thus, evoked and induced magnetic brain activity revealed a differential sensitivity to elements of cognitive processing during the given task.