Dear all,

I would like to optimize my design by inserting null-events between my trials (in order to better catch the HRF shape with reasonable duration of the experiment) using optseq.

I'm not very familiar with this useful tool and I wonder if you could check my setup?

Here my design :

I've got 12 trials per run (2 runs per participants). Each of my trial is 34s long and is composed as follow :

-An instruction reminder screen of 4s

-A video stimulus of 12s to 20s. This screen will be my "stimulus of interest". It's followed by a fixation cross in such a way that their cumulated durations will not exceed 20s

-A question about the video followed by a fixation cross in such a way that their cumulated durations will not exceed 20s.

-A jitter (a fixation cross), determined by optseq

It's a 2 (A1; A2) x2 (B1; B2) design and I'm interested in these following contrasts:

A1 vs A2

B1 vs B2

(The interaction contrast will have an exploratory value in my analysis.)

In order to determine the jitters and the order of the stimuli, I set the optseq as follow:

--ntp 210\

--tr 2\

--psdwin 0 40 1\

--ev evA1B1 34 3\

--ev evA1B2 34 3\

--ev evA2B1 34 3\

--ev evA2B2 34 3\

--ecv 1 1 -1 -1\

--evc 1 -1 1 -1\

--nsearch 10000\

--nkeep 3

I'm not very confident with my setup and if it's correct?

I also wonder if I correctly set the ev durations and the psdwin. The stimulus of interest is the video but I set the ev using the trial duration in order to obtain ITI jitters and psdwin to the trial duration.

This results in a poor efficiency and I wonder if it's possible to better optimized this design...

Any help will be appreciated...

Regards,

Alexandre