Figure 4.

The topography of the alpha activity is modulated by covert attention in different directions. This opens the possibility of making a BCI system which tracks attention in two dimensions. (A) Subjects were asked to covertly attend to one of eight directions for a 1300-ms period while fixating centrally. During this interval the alpha power was estimated using data from a 128 channel EEG system. The resulting topographies for the eight direction are shown. Both vertical and horizontal directions of covert attention clearly modulated the distribution in the alpha band. Reproduced with permission from Rihs et al. (2007). (B) In an MEG experiment subjects were asked to continuously track the direction of a target moving on a circle while fixating at the central cross. (C) The directions of attention were arbitrarily divided into 16 subparts and the respective alpha power was estimated using at 275 sensor MEG system. The topography of the alpha band activity is clearly modulated by the direction of attention. (D) The direction of covert attention was estimated from 1700 ms data segments. The true angle of the target could be predicted from the alpha activity alone with some error (top panel). After a smoothness constraint was applied (lower panel), the prediction error was much reduced. [(B,C,D), top panel] Reproduced with permission from Bahramisharif et al. (2010b).