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Joseph Schmidt, Steven G. Luke, John E. Richards, John M. Henderson; Co-registration of eye movements and event-related potentials in reading. Journal of Vision 2013;13(9):795. doi: 10.1167/13.9.795.
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Eye-tracking has become a nearly ubiquitous tool that provides an online measure of information processing across a variety of tasks. Likewise, event-related potentials (ERPs) provide an online measure of neural processing. Recent work has attempted to combine these techniques and co-register the eye movement record with the electroencephalography (EEG) waveform, allowing for the analysis of ERPs time locked to fixation onset. However, an impediment has been eye-movement-related EEG artifacts(e.g. Dimigen, Sommer, Hohlfield, Jacobs, & Kliegl, 2011). Our method for co-registration uses Independent Components Analysis (ICA) to identify and remove the components resulting from eye movement activity. After removal, the residual EEG activity was reconstructed and analyzed for fixation related ERPs. The eye movement components were identified using three criteria: (1) the component loadings on the surface of the head were consistent with an eye movement; (2) source analysis localized the component to the eyes, and (3) the temporal activation of the component occurred at the time of the electrooculogram activity in the eye and differs for right and left eye movements. This method was tested in the context of a connected text reading paradigm in which observers read paragraphs of normal text or pseudo-text. In the normal text condition subjects read paragraphs, whereas in the pseudo-text control condition observers "read" through a font in which each letter was replaced by a geometric shape that preserved word location and word shapes but eliminated meaning (see Henderson & Luke, 2012). The corrected EEG waveform was aligned to word fixation onset and early results suggest P1 and N1 differences between text and pseudo-text conditions as well as trends towards frequency effects in the text condition. These results suggest that the co-registration of eye movements and ERPs can be successfully combined to investigate a wide variety of tasks.
Meeting abstract presented at VSS 2013
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