Makeig, Westerfield, Townsend, Jung, Courchesne and Sejnowski (Trans Roy Soc, 1999), "Functionally independent components of early event-related potentials in a visual selective attention task."

Published paper


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Figures

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Fig. 2a

Fig. 2a...

Figure 2a. The grand mean response for all 20 nontarget conditions and 20 subjects. Responses at all 29 scalp channels are shown on the same baseline. Note that N1 component peak latency differs at each electrode site. The scalp maps illustrate the continuously shifting potential distribution through the N1 peak. The maps have been scaled individually to their minimum and maximum values to highlight shifts in the scalp distribution of the response.

Fig. 2b


Fig. 2b...

Figure 2b. Scalp maps of the largest six independent components, individually scaled (green represents zero weight). Relative locations of the electrodes are shown by small dots. Color polarities are chosen to represent the signs at their time point of maximum projection (red positive, blue negative with respect to the reference). Note the bilateral near-symmetry of the two early-N1 components (top row).

Fig. 2c


Fig. 2c....

Figure 2c. The upper (colored) traces show the grand mean target response averaged across all 20 subjects and 5 target conditions at the 29 scalp channels. The time series defined by the most positive and most negative potential values across all channels at each time point may be termed the 'envelope' of the response, as shown in the lower panel (black traces). Conventional peak labels are shown.

Fig. 2d


Fig. 2d....

Figure 2d. Envelopes of independent components N1aL and N1aR in the grand mean responses to non-target stimuli presented at far right, central, and far left locations respectively. The vertical dashed lines mark 162 msec. Note the stable component peak latencies across conditions, and their ~9 msec difference. Envelopes computed across 29 scalp channels.

Fig. 3


Fig. 3....

Figure 3. Envelopes of the six largest independent components (black outline, filled with red, from all 31 channels) (cf. Fig. 1c above), superimposed on the mean response envelopes for all 25 Presented/Attended Location conditions. Note the systematic differences between the sets of conditions in which the different components are active: N1aL and N1aR (top row) are evoked by left and right visual field stimuli, but do not appear to depend in any simple way on the attended location. Both also respond to midline stimuli. N1b (center left) responds to right visual field stimuli. Its amplitude is enhanced both in attended locations and to a lesser extent in nearby right visual field locations (locations (4,5) and (5,4)). P2a, by contrast (middle right), has little or no response to targets (diagonal traces). Its amplitude is generally largest to nontarget midline stimuli. Components P3f (lower left) and P3b (lower right, amplitude clipped) account for overlapping early and middle portions of the late positive complex ( Makeig et al., J. Neurosci., 1999) in responses to target stimuli presented at attended locations.