Abstract:
VanRullen and Mcdonald investigated the impulse response function of the brain by cross-correlating random luminance sequences with the simultaneously recorded EEG data. Surprisingly the resulting impulse response function showed a strong and long lasting 10 Hz component, that showed increased power, as a result of high visual attention. In this MEG experiment, we aimed at investigating the effect of top-down attention on the alpha power of these so called perceptual echo functions, in a cross-modal attention task. Moreover, we were interested in investigating the relationship between ongoing alpha oscillations, perceptual echoes and gamma activity. We found increased alpha power in the perceptual echoes as a result of low visual attention. Furthermore, we were able to show increased posterior alpha power during random visual stimulation, and provide evidence for a phase locking of posterior gamma activity to alpha oscillations. Finally our findings suggest that bottom up visual processing of random visual sequences is reflected in the posterior gamma activity.
