Visually induced gamma-band responses to coherent and incoherent motion: a replication study.

The present study was based on earlier findings that the observation of a coherently moving long bar induced gamma-band activity in humans. The power in the EEG-gamma-band was reduced during the presentation of two incoherently moving short bars. The present study demonstrates the replicability of this cortical activity pattern and illustrates intersubjective variability in its topography. In addition, cortical alpha-activity was examined to test whether gamma-band activity might reflect changes in harmonics of alpha waves. Results indicate that induced gamma-band activity cannot be secondary to changes in the amplitude of alpha waves, since the latter would require both a similar time course of both frequency bands while stimuli are in motion and an identical topographical pattern. The present results suggest that oscillations in the gamma- and the alpha-bands are two different brain activities, with different functional implications.