N-Back Task (letter stimuli)


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mjeeves
mjeeves
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Hi


I'm modifying the script for the N-Back Task (letter stimuli) so that it only includes the 1, 2 and 3-back levels, i.e. I have deleted the 0-back level.


When testing the script I see this error message: "Unable to initialize <picture expinstructionslide> item number 4. Verify the item exists and is correctly defined."


Evidently I need to change something in the Instruction script, however, I can't figure out what that may be. Here is the script I have for Instruction Image Selection:




***********INSTRUCTION IMAGE SELECTION******************************************


<picture SingleNbackinstructions_start>


/ items = Nback_startinstructions


/ select = sequence


/ size = (100%, 100%)


</picture>



<picture Practice_end>


/ items = practiceend


/select = 1


/ size = (100%, 100%)


</picture>



<picture StartExp_slide>


/ items = startendslides


/ select = 1


/ size = (100%, 100%)


</picture>



<picture EndExp_slide>


/ items = startendslides


/select = 2


/ size = (100%, 100%)


</picture>



*instructions for individual experimental trials are selected depending on level of N


<picture expinstructionslide>


/items = expinstructions


/select = expressions.selectinstruct


/size = (100%, 100%)


</picture>



<picture repeatpractice_page>


/items =  ("SingleNbackInstructions_practicerepeat.gif")


/size = (100%, 100%)


</picture> 




Dave
Dave
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<picture expinstructionslide>


/items = expinstructions


/select = expressions.selectinstruct


/size = (100%, 100%)


</picture>



You need to check that expression.


mjeeves
mjeeves
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Thanks Dave, that worked a treat.


NBuch
NBuch
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I´ve got the same problem and I don´t know how to change expressions.selectinstruct.

<expressions>
/selectinstruct = values.N + 1
</expressions>

Thanks!


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Dave
Dave
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You need to make sure that the expression never returns an invalid index. See the comments in the script and look at how the index is computed (i.e., trace the usage of values.N throughout the script; hit CTRL+F and search for values.N).

If you simply remove stuff without paying attention to that, things will break.

GO

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