Quantitative analysis of EEG signals: Time-frequency methods and ...

Figure 4: Averaged responses upon NON TARGET and TARGET stimuli of a left
occipital electrode in pattern visual evoked potentials
1.3 Relation between EEG and ERP
In contrast with the conventional view of ERPs as signals being added to the noisy
EEG, Basar (1980) pointed out that ERPs might arise from the ongoing EEG by means
of a resonance process. Resonance is awell known phenomenon of physics: if a driving
is applied to a system, for example a pendulum, the system will show very large and
increasing outputs if the driving frequency is similar to the natural frequency of the
system (for a physical description see Feynman et al., 1964). Basar (1980) introduced
the following concept for understanding the relation between EEG and ERP: In the
EEG several oscillations are occurring at the same time in a non-synchronized way, and
when a stimulus is applied, some of these frequencies can be enhanced by a resonance
phenomenon. Furthermore, it was assumed that these dierent enhanced oscillations
are related to transmitting information through the brain, having dierent \meanings"
and \functions" (see sec. x2.3.3). According to a classication of Galambos (1992)
event related oscillations can be evoked (originated by and time locked to the stimulus),
induced (originated by, but not time locked to the stimulus) or emitted (originated by
an internal process rather than by the stimulus).
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