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Interpreting HRF export-Extracting analyzed data values  

Nicollette Purcell
Posts: 4
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New Member
Joined: 4 months ago
Hi Meryem,
I was wondering if you could provide some insight into how to interpret the exported HRF data from Homer3, or if you had any resources to help us do so. We are new to Homer and attended the most recent training course, however, we are unfamiliar with handling analyzed data once exported to a .txt document. I transferred some exported HRF data from the original .txt file to an excel document to view it more clearly. One thing we were confused about is that the exported HRF document includes values from the time preceding the stimulus onset (the negative time points), so we were unsure if we had to normalize the baseline to zero ourselves first, before calculating averages for the channels and subsequent brain regions. Or if there is a different way to extract the block average results. I could not find a post on the forum addressing interpreting the exported HRF output and I want to ensure we understand what we are looking at and run statistics correctly on our processed data. Any guidance is appreciated.
Thanks again,
Nicollette Purcell
1 Reply
Meryem Yücel
Posts: 8
Joined: 6 months ago

Nicollette, please plot the first column of the excel file (time) and any other column (e.g. the second one), you will see the HRF is baseline corrected i.e. you will see that the values before 0 are around 0 since the whole HRF time course is baseline subtracted within the GLM function (by the mean of the time range before stim that you picked e.g. -2 to 0, if the trange you picked is -2 to 10). For stats you can take the mean of the HRF around the peak activation, this will change depending on your stimulus type and duration.