Examined Event-related Potentials Research Articles

Gamma responses and ERPs in a visual classification task

Objective: We examined event-related potentials (ERPs) and gamma range EEG activity in a visual classification task to assess which variables affect these responces.Methods: Ten subjects silently counted the occurrence of rare Kanizsa squares (targets) among Kanizsa triangles and non-Kanizsa figures (standards). By applying a time-frequency analysis to the data and selectively calculating topographical maps of certain frequencies.Results: We were able to find 3 different types of gamma responses to Kanizsa figures: an early phase-locked gamma response at 40 Hz in the N100 time range, late phase-locked gamma activity (200–300 ms) at 40 Hz and a continuous phase-locked gamma response at 80 Hz due to the monitor refresh frequency. The two 40 Hz responses were significantly higher for Kanizsa figures than for non-Kanizsa figures and within the Kanizsa figures were higher for the target figure than for the non-target.Conclusion: The phase-locking of these two responses, previously found also as non-phase-locked activity, could be synchronized due to the monitor flicker frequency. Also, our findings suggest that the gamma responses are not solely associated with the binding of stimulus features, but reflect some processes related to target processing.

Electrophysiological indicants of black-white discrimination performance for letter and non-letter patterns

This study examined event-related potentials (ERPs) and behavioral measures, considered to be sensitive to the selective processing of black versus white letter and non-letter patterns, in a group of seventy-four randomly selected 6 to 8 year old children. Results demonstrated faster and more accurate behavioral performance on the experimental task for the letter than for the non-letter patterns. The ERP measures provided complementary information regarding this letter facilitation effect, indicating that the selective neural processing of letter as compared to non-letter patterns was present in the electrophysiological waveform within the initial 100-140 ms after stimulus presentation. Later ERP measures (200-260 and 500-600 ms post-stimulus) in response to the letter stimuli showed greater differences as a function of task relevance over the left than over the right hemisphere. The results from the present study indicate a remarkably early facilitative influence of stimulus type (letter versus non-letter patterns) on the luminance discrimination of these stimuli and are consistent with an overlap of linguistic and perceptual processing.