Figure 1.
Comparision of conventional and generalized ERD.
Conventional ERD (panel A) measures the deviation of the event-related dynamics (blue solid line) from a constant baseline level (black dashed line) that is obtained as averaged power in the reference period . The generalized ERD (gERD), depicted in panel B, defines ERD/S in relation to a dynamic reference (black dashed) which is obtained from catch trials. The reddish and bluish areas of both panels indicate the resulting periods of ERD and ERS, respectively.
Figure 2.
Surrogate data of ongoing activity and the dampening process.
Panel A exemplifies two different realizations of the parameterized function , simulating the power envelopes (bold lines) of rhythmic ongoing activity. To establish a better understanding, we also depicted the corresponding oscillations (thin lines) beside the power envelopes. Panel B depicts the multiplicative dampening factor
at three different values of the parameter
.
Figure 3.
Comparison of both methods for the estimation of state conditional ERD by means of surrugate data.
The figure contrasts the true conditional ERD (left column), the estimated conventional conditional ERD (central column) and the estimated generalized conditional ERD (right column). Each row corresponds to a particular artificial data set (I–III, top to bottom). The panels share an identical color coding scheme, where blue and red refer to ERD and ERS, respectively. The vertical and horizontal axes represent the state variable and the time, respectively.
Table 1.
Analytic solutions of conditional ERD for the three artificial datasets.
Figure 4.
Schematic layout of a single trial.
After a first priming stimulus a second stimulus is delivered randomly at a predefined inter-stimulus interval. The responses to the second stimulus are then used for the analysis of conditional ERD.
Figure 5.
Comparision of both methods for estimating state conditional ERD induced by somatosensory stimuli.
The figure contrasts the conventional (panel A) with the generalized state conditional ERD (panel B). The vertical axis represents the explanatory factor, i.e., the level of pre-stimulus activity. The estimated ERD/S are depicted using a color coded scheme, where blue dyed areas correspond to periods of ERD while red dyed areas indicate an ERS. The additionally highlighted horizontal lines correspond to the individual panels of Fig. 6.
Figure 6.
Estimated state conditional event-related and reference dynamics of the .
The individual panels A–C correspond to high, medium and low level of local pre-stimulus . The dyed areas indicate the periods of ERD (blue) and ERS (red) identified by the generalized framework. The horizontal line in each panel illustrates the static baseline level of the conventional ERD, while the conditional event-related and reference dynamics are depicted by the solid and dashed dynamics, respectively.
Figure 7.
Estimated functional relationship between the ERD characteristics and the explanatory factors.
Panel A shows the estimated dependency of ERD magnitude on the three explanatory factors, i.e., on the local pre-stimulus (solid), on the pre-stimulus activity of occipital
(dash-dotted) and on the strength of the preceding ERS response (dashed). The estimated relationship between ERD latency and the three factors is depicted in panel B.