Hi Jack,
thanks for all the time you are giving me (us).
I hope this thread could help many other people.
>>> What exactly is the contrast that you are trying to make?
we have three tasks (only the cue stimulus changes), each performed by a different group (subj number: 15, 15, 12).
each task has 6 conditions (55 trials each): 2 congruent, 2 incongruent, 2 neutral.
i'm trying to see why, in task1 and 2, one congruent condition facilitate the response and the other not and why this effect disappears completely in task3.
I assume, maybe wrongly, that I have to make a contrast with the EV representing the target. making a [1 ..... -1 ....] or [1 1 ..... -1 -1 .....], according to EV model.
till now, i have some activation comparing two groups, but when i look in a single group/task where I have a signif difference in RT data, the contrast CongrA > CongrB produces empty images.
>>>What is the interval between Response1 and Cue2?
zero, when subject press the button, the second target/cue appears.
I'm not interested in what happens after response1. actually, as seen by our EEG analysis (we also recorded the ERP of the same task in the same subjects), we are interested in the 100-400ms after target onset
>>>What is the intertrial interval? Are these intervals constant or variable?
intertrial interval varies randomly between 1000-1500ms after second button press. so the latter event and next cue onset are separated by 1700-2700 ms. (a fixation point appear at the beginning of each trial, 1000 ms before the cue)
>>>Are the trial onsets or stimuli onsets jittered relative to the TR?
no
>>>What are the typical mean RTs?
700-900 ms . standard deviation is around 150-250 ms
between congruent A (facilitating) and congruent B (no facilitating) there are around 40-60 ms.
thanks and cheers
Alberto
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