Millisecond Forums

For the 'facesneutral' and 'erasewords' stimuli at least you will have to work with the setstimulustime() function which can be found in the documentation for the <trial> element.

You cannot use expressions directly in /stimulustimes.

Fabian,

I have been having a similar issue. In my case, I want trials where the fixation cross duration is variable between 750 and 1500 ms. Did you ever find a solution to this problem?

Thanks,

Zan

As already mentioned in my reply: You can achieve dynamic stimulus timings via trial functions such as setstimulustime(), insertstimulustime() etc. as detailed in the language reference for the <trial> element.

EDIT: Here's a quick, self-contained example illustrating one way to use these functions:

<list fixationduration>
/ items = (500, 5000, 10000)
</list>


<trial mytrial>
/ ontrialbegin = [trial.mytrial.setstimulustime(text.a, list.fixationduration.nextvalue);
    trial.mytrial.insertstimulustime(text.b, list.fixationduration.nextvalue)]
/ ontrialend = [trial.mytrial.resetstimulusframes()]
/ stimulustimes = [0=fixation]
/ validresponse = (57)
</trial>

<text fixation>
/ items = ("+")
</text>

<text a>
/ items = ("A")
/ position = (45%, 50%)
</text>

<text b>
/ items = ("B")
/ position = (55%, 50%)
</text>

<block myblock>
/ trials = [1-3=mytrial]
</block>

Alternatively, you can simply have your fixation cross displayed by a separate <trial> element and control / change its duration via the /trialduration attribute (which does accept variables).

Thanks for this! I will try this method, too. I just had success with using fixation cross as a separate trial, then blocking them such that the even numbers were fixation crosses and odd numbered trials were my stimuli/"real" trials. Here is my abbreviated syntax for future viewers:

<expressions>

/fixduration = rand(750,1500)

</expressions>

<trial fixation>

/stimulustimes = [0=fixation]

/trialduration = (expressions.fixduration)

/correctresponse = (noresponse)

</trial>

<trial ANG_congR>

/stimulustimes = [0=ANGfacesR,NEUfacesL; 125=eraser,probeR]

/correctresponse=("I")

/validresponse=("E","I")

/pretrialpause=0

/timeout=3000

</trial>

<block practiceblock>

/trials=[1=blockpause; 2,4,6,8,10,12,14,16,18,20=fixation; 3,5,7,9,11,13,15,17,19,21=noreplace(ANG_congR)]

/preinstructions=(intro1, intro2, intro3)

/recorddata=false

/postinstructions= (begin)

</block>