This data example gives dramatic evidence of the power of infomax ICA to separate temporally and functionally distinct processes from 100-channel data in an event-related EEG experiment (from Onton & Makeig (2006) -- 36 MB pdf!). The figure illustrates well how the distinct features of cortical and artifact dynamics contributing to the scalp data and separated from the data by ICA (bottom panel). are otherwise difficult or impossible to extract from the original scalp channel data (top panel).
Figure. Fifteen seconds of EEG data at 9 (of 100) scalp channels (top panel) plus contributing activities of 9 (of 100) independent components (ICs, bottom panel) extracted from the whole session data. While nearby electrodes (upper panel) record highly similar mixtures of brain and non-brain activities, ICA component activities (lower panel) are temporally distinct (i.e., maximally independent over time), even when their scalp maps are overlapping. Compare, for example, IC1 and IC3, accounting for different phases of eye blink artifacts produced by this subject after each visual letter presentation (grey background) and ensuing auditory performance feedback signal (colored lines). Compare, also, IC4 and IC7, which account for overlapping frontal (4-8 Hz) theta band activities appearing during a stretch of correct performance (seconds 7 through 15). Typical ECG and EMG artifact ICs (IC12, IC55) are also shown, as well as overlapping posterior (8-12 Hz) alpha band bursts (IC5, IC98) that appear when the subject waits for the next letter presentation (white background) For comparison, the repeated average visual event-related potential of a bilateral occipital IC process (IC5) time locked to the visual stimulus is repeated (in red) on the same (relative) scale as the component activity. Clearly the unaveraged activity dynamics of this IC process are not well summarized by its averaged response a dramatic illustration of the independence of phase-locked and phase-incoherent activity.