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N-Back Task (letter stimuli)

mjeeves — Tue, 09 Dec 2014 05:58:11 GMT

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******************************************

/ items = Nback_startinstructions

/ select = sequence

/ size = (100%, 100%)

</picture>

/ items = practiceend

/select = 1

/ size = (100%, 100%)

</picture>

/ items = startendslides

/ select = 1

/ size = (100%, 100%)

</picture>

/ items = startendslides

/select = 2

/ size = (100%, 100%)

</picture>

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

/items = expinstructions

/select = expressions.selectinstruct

/size = (100%, 100%)

</picture>

/items = ("SingleNbackInstructions_practicerepeat.gif")

/size = (100%, 100%)

</picture>

RE: N-Back Task (letter stimuli)

Dave — Tue, 09 Dec 2014 05:58:11 GMT

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.

RE: N-Back Task (letter stimuli)

NBuch — Tue, 09 Dec 2014 05:16:22 GMT

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

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

Thanks!

RE: N-Back Task (letter stimuli)

mjeeves — Wed, 17 Apr 2013 03:40:23 GMT

Thanks Dave, that worked a treat.

RE: N-Back Task (letter stimuli)

Dave — Wed, 17 Apr 2013 02:14:01 GMT

[quote]

/items = expinstructions

/select = expressions.selectinstruct

/size = (100%, 100%)

</picture>

[/quote]

You need to check that expression.