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</o:shapelayout></xml><![endif]--></head><body lang=EN-GB link=blue vlink=purple><div class=WordSection1><p class=MsoNormal>Dear EEGLAB Team<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>There is always the discussion about how many samples are needed for a good ICA and based on the tutorial pages from your lab it seems to be quite many. People that use high density EEG with 128 electrodes would likely need ~1000000 data points, which means more than 1 hour of EEG recording (considering we do downsample to 250 Hz). I doubt that all of us have recordings that are that long. At least I often have tasks that last for ~ 10-20min. One idea that I thought of is to merge datasets of a person if she/he had multiple sessions on the same day with the same task (that is having the same net application). I would like to hear your opinion about this idea, whether you also do this approach and what I should consider when merging files.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Here is a specific example: I tried this approach for a visual memory task during which my participants were seeing and rating pictures before a nap and after a nap. I merged the two datasets and after preprocessing (filter, clean_rawdata, interpolation, average referencing) I performed an ICA (tried both AMICA and RUNICA, results are very similar). The components seemed to be captured fine, however I clearly saw that many of the signals (e.g. muscle, but also physiological brain components) changed in activation after the transition of the merged files. More specific, the components were capturing the same type of activity (e.g. muscle, eye blinks or alpha) but the amplitudes of the component clearly changed between the first and second data set. That is for instance one muscle component had strong activation in one dataset and was very low amplitude in the second part of the data. People are likely more relaxed after sleep, are maybe more focussed and I was wondering whether merging of datasets is not ideal because conditions are slightly different and I even expect that oscillatory activity relative to the stimuli will slightly differ before and after sleep for the same task. What is your impression? Would you rather process the files separately or merge them together to one?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Thanks for your valuable input and best wishes,<o:p></o:p></p><p class=MsoNormal>Caroline<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>