Millisecond Forums

randomizing which stimuli appear during a block

https://forums.millisecond.com/Topic35519.aspx

By nc - 7/6/2023

Hi,
I have 8 sets of pictures, and I want each of them to appear randomly in each of 8 blocks (no replacement). I did something like this (note: code not exact, because I am not currently able to access the script), but it doesn't seem to be working. Would you be able to advise?

<list stimuli>
/items = (picture.1, picture.2. picture.3., picture.4, picture.5, picture.6, picture.7, picture.8)
/selectionrate = block
/replace = false
</list>

<block test>
/trials = [1=trial, 2 = trial2]
/bgstim = stimulus1, stimulus2, stimulus3, list.stimuli
</block>
I know the above isn't quite right, but what I'm trying to do is include a randomly selected picture from the list as background stimuli within that block. I'm also trying to make sure that no picture appears more than once across 8 different blocks.
By Dave - 7/7/2023

 
nc - 7/7/2023
Hi,
I have 8 sets of pictures, and I want each of them to appear randomly in each of 8 blocks (no replacement). I did something like this (note: code not exact, because I am not currently able to access the script), but it doesn't seem to be working. Would you be able to advise?

<list stimuli>
/items = (picture.1, picture.2. picture.3., picture.4, picture.5, picture.6, picture.7, picture.8)
/selectionrate = block
/replace = false
</list>

<block test>
/trials = [1=trial, 2 = trial2]
/bgstim = stimulus1, stimulus2, stimulus3, list.stimuli
</block>
I know the above isn't quite right, but what I'm trying to do is include a randomly selected picture from the list as background stimuli within that block. I'm also trying to make sure that no picture appears more than once across 8 different blocks.


You don't want a list. You want a <picture> element with eight items, set to random selection without replacement and /selectionrate set to block. I.e.

<picture bgpic>
/ items = bgpicitems
/ select = noreplace
/ selectionrate = block
</picture>

<item bgpicitems>
/ 1 = "01.jpg"
/ 1 = "02.jpg"
/ 1 = "03.jpg"
/ 1 = "04.jpg"
/ 1 = "05.jpg"
/ 1 = "06.jpg"
/ 1 = "07.jpg"
/ 1 = "08.jpg"
</item>

<block exampleblock>
/ bgstim = (bgpic)
/ trials = [1=mytrial]
</block>

<trial mytrial>
/ validresponse = (57)
</trial>

<expt>
/ blocks = [1-8 = exampleblock]
</expt>