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Select subset of image stimuli

I have a list of 180 conditions and 2 parameters. I need to divide it in 4 chunks and assign each chunk randomly to participants.

How can I do it from the builder?



Hi Dani,

Do you want each participant to randomly see 45 conditions or have your participants in four separate groups with participants in the same group seeing the same 45 conditions?

Are you wanting to put this online? If so, do you want the same number of participants in each group or is random assignment good enough?

Best wishes,


Hi Wakefield,

thanks for replying.
Yes, I want to put it online (this is my first exp) and I would like to have at least 5 judgments for each stimuli.

So, my idea is to have the stimuli divided in four parts and participants in the same group see the same stimuli, and because each stimulus must receive the same number of judgments, the number of participants for each group should be the same. Does it make sense to you? :slight_smile:


In that case I would recommend that you use my new online app

You can then either set the experiment as having 4 groups (£10 licenced version which compensates for participants who fail to finish) or use participant%4 (free version)

The following code goes in Begin Experiment and for group you’d need to add group to the expInfo dialogue box.

if expInfo['group'] == 1:
     useRows = "0:45"
elif expInfo['group'] == 2:
     useRows = "45:90"
elif expInfo['group'] == 3:
     useRows = "90:135"
elif expInfo['group'] == 4:
     useRows = "135:180"


if int(expInfo['participant'])%4 == 0:
     useRows = "0:45"
elif int(expInfo['participant'])%4 == 1:
     useRows = "45:90"
elif int(expInfo['participant'])%4 == 2:
     useRows = "90:135"
elif int(expInfo['participant'])%4 == 3:
     useRows = "135:180"

then put useRows in the selected rows of the loop.