Dear Freesurfer list,
I am using optseq2 for the first time and wanted to check with you whether my protocol makes sense, many thanks in advance for your insight.
1) I start by choosing the maximum scan duration equalling ~30 min: 2) set the psd window so it can capture the entire waveform of a 4 second event 3) select equal amounts of trials for each of the 4 event types, I played around with it and 80 trials give me the greatest efficiency (2.72) and variance reduction factor average (54.37). Are these values acceptable? They are the best I could get tweaking the number of trials.
The command is here:
./optseq2 --ntp 440 --tr 4 --psdwin 0 20 \ --ev evt1 4 80 \ --ev evt2 4 80 \ --ev evt3 4 80 \ --ev evt4 4 80 \ --nkeep 3 \ --o gfatrial \ --focb 10 \ --nsearch 10000
A sample trial list is here:
0.0000 2 4.000 1.0000 evt2 4.0000 4 4.000 1.0000 evt4 8.0000 0 4.000 1.0000 NULL 12.0000 3 4.000 1.0000 evt3 16.0000 3 4.000 1.0000 evt3 20.0000 2 4.000 1.0000 evt2 …
The other question I had concerns the position of null trials. Many trials are not separated by a NULL event, however studies of rapid event-related designs to report a minimum ITI, in this case the minimum seems to be 0? To assess the effect of forcing a minimum ITI on the sequence, I have run the search defining the --tnullmin to 4 sec (equal to 1 TR) however efficiency and VRFAvg drop to .79 and 16.07, obviously due to trade of between ntp and ntrials (ntp=440, ntrials=62).
Are NULL trials between each event required at all if a standard FIR is used for the analysis? My aim is to first apply a univariate BOLD-analysis and subsequently a multivariate analysis to the dataset. Thanks for clarifying.
Betina