Tutorial 9: Select files and run processes

Authors: Francois Tadel, Elizabeth Bock, Sylvain Baillet

The event markers that are saved in the file might not accurate. In most cases, the stimulation triggers saved by the acquisition system indicate when the stimulation computer requested a stimulus to be presented. After this request, the equipment used to deliver the stimulus to the subject (projector, screen, sound card, electric or tactile device) always introduce some delays. Therefore, the stimulus triggers are saved before the instant when the subject actually receives the stimulus.

For accurate timing of the brain responses, it is very important to estimate those delays precisly and if possible to account for them in the analysis. This tutorial explains how to correct for the different types of delays in the case of an auditory study, if the output of the soundcard is saved together with the MEG/EEG recordings. A similar approach can be used in visual experiments using a photodiode.

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