Occurrence of the electroencephalographic alpha rhythm with eyes open.

Abstract

IT is well established in electroencephalography that the alpha rhythm occurs much less frequently when the eyes are open in an illuminated environment than when they are closed. Moreover, if the visual enviroment is patterned, then alpha occurrence is even less frequent. Finally, ‘paying attention’ to the pattern reduces the occurrence of alpha still further1. Although these general descriptions are valid, they can be misleading if one wrongly assumes that ‘much less frequently’ means a very low frequency of occurrence of the alpha rhythm. On the basis of such an assumption one might not attempt certain experiments concerning vision and the alpha rhythm, because the expected amount of alpha rhythm would be too little.