Hi all,
I have been advised to use optseq to aid my event related fMRI design, specifically to help calculate stimulus order and timing. I've read the help in some detail but am still a little unclear on some of the appropriate values to input and indeed what values I am aiming for in the output. It'd be great if anyone can help out...
Briefly, my study is a simple food cue reactivity study in which three different types of pictures (50 each) are presented for 3s each, in pseudo-random sequence. I now intend to include null events to optimise the spacing of the events to detect a difference between conditions, but also to provide a baseline for a 'sanity check' just in case.
I am uncertain as to the value of psdwin and associated variables (PSD, min, max dPSD) - should I include a post-stimulus delay or should that be set to 0 as in most examples? Also what is the recommended psdwinMAX value for events of 3s? 12 or as much as 18 seconds to capture the whole haemodynamic response?
Also I am not certain how to judge the resulting output. I understand I should maximise 'efficiency' but I can't find any advice as to what is a 'good' value of efficiency to aim for. Any advice here? Also should I be judging the sequence on any other values?
So I have inputted the following and got a value of 2.586 for efficiency for the best sequence. Is this reasonable/sufficient?
optseq2 --ntp 200 --tr 3 ---psdwin 0 12 3 --ev ev1 3 50 --ev ev2 3 50 --ev ev3 3 50 --nkeep 3 --o test6 --nsearch 10000
Many thanks in advance,
Ella