Figure 2. Grand average of occipital time-frequency modulations in experiments I+II.

a)+e) 2-D topographies of the alpha-rhythm suppression in the ISI (500 ms, 10 Hz) are plotted. Ellipses enclose the occipital regions of interest. b+d) Grand averages of time-frequency matrices for the occipital regions of interest for the cueing task and the control tasks (b) separately for the three validity conditions (d). Zero on the x-axis corresponds to the onset of the S₁ stimulus. The black vertical line in the results of the cueing task marks the onset of the S₂ stimulus. Black squares designate the time-frequency window in which the alpha-rhythm suppression was analyzed. c+f) The topography plots illustrate the laterality of the alpha-rhythm suppression in the cueing task. The amount of stimulus-locked oscillations at various times and frequencies relative to the pre-stimulus baseline is color-coded and is expressed in db. In a), b), d), and e) positive values indicate an increased, while negative values indicate a decreased amount of stimulus-locked oscillations. In c) and f) positive values indicate stronger alpha-rhythm suppression after left than after right finger stimulation, while negative values indicate stronger alpha-rhythm suppression after right than left right finger stimulation.