Randomisation across blocks

[River]

Hi,

I am trying to randomise stimuli across two test blocks using the
following List settings:

TestBlock1
41 random images(unrepeated) from ListA
1 cue image_1
3 random images (unrepeated) from ListA

TestBlock2
41 random images (unrepeated) from ListA
1 cue image_2
3 random images (unrepeated) from ListA

The random images all come from the same list (BlockListA) with two
nested lists, Target absent images (containing 43 images) and Target
present images(containing 45 images). Each of the two cue images have
a separate list to themselves.

The TestBlocks state the order should be sequential while BlockListA
and the Target Absent and Target Present nested lists both state
ordering should be random (without replacement).

When i run the experiment one of the target absent images is repeated
instead of showing the final target present image. I can't understand
why the randomisation is working across these test blocks for all bar
a single image (not the same one each time)!!

I've changed the experiment to the following structure:

TestBlock1
45 (sequentially ordered) images from BlockListA

TestBlock2
45 (sequentially ordered) images from BlockListB

Where BlockListA states (sequential ordering):
41 images from TargetList (which contains both target absent and
target present images)
1 image from Cue_1
3 images from TargetList

Where BlockListB states (sequential ordering):
41 images from TargetList (which contains both target absent and
target present images)
1 image from Cue_2
3 images from TargetList

Where TargetList ordering is random without replacement. This seems to
work (i've run the experiment 8 times so far with no duplicates/
missing images) but i'd like to know why this would work instead of
the above described experiment as essentially the only difference is
that the random images are all in the same list and the sequential
ordering of 41 random images, 1cue, 3 random images is described later
on in the list structure (i.e. in BlockListA not TestBlock).

I hope this is clear enough! Any advice would be much appreciated.

[liwenna]

Hey River,

Your question for six days now. Personally I find it hard to see what
could be wrong based on the info given. Could you perhaps post a
screenshot of your setup, make it so that all the relevant lists are
opened and visible, so that the settings are shown (for an example see
this screenshot which was made for another thread ttp://images.redial.net/kkat.bmp).

Or if you have solved problem by now... what was it?

Best regards,

liwenna

[River]

Hi Liwenna,

I appear to have solved it-I rearranged the structure slightly to that
listed above however to be honest I don't completely understand why
that would have worked other than perhaps causing the programme to not
have to struggle through multiple Lists. My other (halfbaked) theory
is that it was attempting to form pairs of images form two different
lists (I had it taking 43 images from list X and 45 from list Y
randomly however it repeatedely was taking 44 from each
instead...hence causing the repetition of one image and missing value
of another image. Now all 88 images are in the same list so once its
run through all of them its done...less confusing somehow i guess?! As
is probably abundantly obvious I have been reduced to vague guesswork
now and am just thankful it seems to be working ok again-fingers
crossed it won't repeat.

thanks for your comments,

River

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