G. Pfurtscheller et al., EVENT-RELATED DESYNCHRONIZATION (ERD) DURING VISUAL PROCESSING, International journal of psychophysiology, 16(2-3), 1994, pp. 147-153
Event-related desynchronization (ERD) is the short-lasting attenuation
or blocking of rhythms within the alpha (beta) band. ERD is found dur
ing but also before visual stimulation. Two different types of ERD can
be differentiated: one short-lasting, localized to occipital areas an
d involving upper alpha components; the other longer lasting, more wid
espread, most prominent over parietal areas and maximal for lower alph
a components. The former most likely reflects primary visual processin
g and feature extraction, the latter is more related to cognitive proc
essing and mechanisms of attention.