By C. Surus. Globe Institute of Technology.
With this system a communication rate of about seven items per minute can be obtained cheap 60 ml rumalaya liniment. When, for example, two items on the monitor are ﬂickering with slightly different frequen- cies in the alpha/beta range, the SSVEP amplitude is enhanced, when the participants shift their gaze to the corresponding light source. The subject has to pay special attention to one of the ﬂashing buttons in order to enhance the amplitude of the corresponding ﬂicker frequency (SSVEP). The implantation of a special electrode into the outer layer of the neocortex allows us to record multiple unit activity in patients. This activity in form of spikes can be transformed into a pulse train and, in turn, can be used for cursor control and selection of letters or other items on a monitor. The type of feedback used in early experiments with the Graz BCI paradigm provided information of a correct versus an incorrect response, as deter- mined by the classiﬁer, at the end of each trial. Further advances in feature extraction methods, such as the implementation of AAR algorithms,73 allow one to calculate the parameters concurrent to the data acquisition. In other words, it was possible to provide instantaneous, classiﬁer-based feedback during deﬁned time periods. This type of feedback indicates in real time how well two EEG patterns (representing, for example, two classes) can be discerned. Using such a continuous feedback system, a general enhancement of performance could be achieved. Data were recorded from the sensorimotor cortex (C3, C4) during imagined movements of the left (thin line) versus right (thick line) hand. The initial recordings without feedback (left panels) reveal a transient desynchronization (ERD) of the mu rhythm over the contralateral hemisphere starting with the cue presentation. Con- tinuously present feedback results in dramatic changes of the ERD/ERS patterns: both subjects show a clearly more pronounced difference between left and right motor imagery during feedback regulation.
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