random trials

One question: I want to have random trials for the serial reaction time task. The trials items must be 1 2 3 4…And the random trials sequence should be for example: 1-3-4-2-3-1-2…
There can be no item repeats…

How can I make such a randomizied sequence without item repeats.

Could someone help me?



and the random trials should be equal across subjects.

Turn randomization On in the Block Editor’s Randomize tab.

thanks :slight_smile: :slight_smile:


Dear Hisham,
but it is complicated if I want to have interstimulus interval between the items.

Without interval it is very easy: I can define my 4 events. Then I can define for exp. 16 trials, and randomize them. And define 1 block for 16 trials. So at the end I have 64 random trials.

but how is possible, when I want to have ISI between 4 items. Now I can not randomize my trials, since this will also cause ISI`s to be randomized like the 4 items.


You can add an ISI as a fifth event within a trial. When trials are randomized within a block, events within a trial are kept in the same order unless you explicitly turn event randomization on yourself.

I hope that I helped more than I confused! :wink:


not clear

Dear Hisham,
I am not sure if it was clear.But before each event there must be a ISI. I show four different pictures at 4 locations, and every time only one picture…A trial is a foursomesequence (like 1-3-2-4)
…And the sequence should change randomly…
Could you help me pls,

Are you trying to get the events to show at specific intervals, or are you wanting a constant delay after the response and before the next event?

If you want the events at specific intervals, you can set up a time limit in the event’s input tab. If instead, you just want a constant ISI between the events, you can create a single ISI event that is run from each stimulus’ feedback. Done either of these ways, the ISI would not be affected by randomizing the events within the trial.

Dear Hank,
I want to have a constant delay between the events.
thanks for your answer!