Having trouble with pictures presenting more than once


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RyanSutcliffe
RyanSutcliffe
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Hi there,

I'm fairly new to Inquisit and have learned the basics for creating an experiment using this tutorial ron.dotsch.org/inquisit-tutorial (it was super helpful!). Although, I am starting to run into some trouble.

My experiment contains pictures across several blocks which I do not want to be replaced; i.e. each stimulus should be presented once in the entire experiment.
I have used the /select = noreplace and /resetinterval = 0 attributes to try and control this, however, on running through my results I have found that sometimes a stimulus would be repeated while another would not be shown at all within the list of 11 possible stimuli. The stimulus that gets repeated or that doesn't appear varies across experimental sessions; i.e. it is a different stimulus each time that is having a problem. I have also had the problem that sometimes 12 stimuli would be selected from one condition, while only 10 would be selected from another, when I simply need 11 to be taken from each condition. I'm not entirely sure what the problem is with the code!
 
If anyone has the time and is willing to help this novice out that would be greatly appreciated! I've attached my exp file and data file. An example problem in the data is that for Participant 3 (the one at the bottom) and looking at the "OrangeIncompHighPL" and "OrangeIncompLowPL" trials, the picture "40.jpg" is being shown twice, while the picture "34 reversed.jpg" is not being shown at all.

I hope my program isn't too messy to understand!

Again any help would be much appreciated!

Ryan Sutcliffe

Attachments
FOOTBALL1.exp (207 views, 21.00 KB)
football1.dat (212 views, 91.00 KB)
Dave
Dave
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The problem is the way you sample trials at the <block> level. E.g.

<block BWLowPL1>
/trials = [1-11=noreplace(BLACKCompLowPL, BLACKInCompLowPL, WHITECompLowPL, WHITEIncompLowPL)]
...
</block>

means sample 11 times (randomly without replacement) from a pool consisting of 4 elements in equal proportions. That, of course, can't work out mathematically, since there is no way to do that (11:4 = 2.75); there can be no such thing as 0.75 of a trial. As a consequence, the pool that is sampled from is larger (each element is in there 3 times) and some trial elements will occur more often than others. A given <block>'s trial selection pool is completely independent of every other <block>'s selection pool, i.e., you have no guarantee whatsoever to end up with the desired amount of trials per type across all blocks.

That, in turn, means that some stimulus elements (here <picture> elements) may be displayed more often than others and more often than they have items -- the consequence is that you see stimuli repeating or some items not being sampled at all (because too few trials displaying the given stimulus have been run).

You'll have to amend your <block>s' trial selection pools accordingly.

RyanSutcliffe
RyanSutcliffe
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Thanks for the quick reply Dave! Thanks for taking a look. I have amended the blocks and all is running smoothly now. 

Cheers

Ryan
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