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Group: Administrators
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Visits: 109K
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#1: If you want only two distinct values for fixduration, you should simply do:
/ ontrialbegin = [values.fixduration = replace(400, 1600)]
#2: You will want to *reset* the stimulus presentation sequence /ontrialend. Otherwise the insertion of stimuli will be cumulative across trials.
/ ontrialend = [trial.practise_trial.resetstimulusframes(); ]
Beyond that, the timings should work out regardless of whether you do
/ontrialbegin = [values.fixduration = 400 + round(rand(0,1))*1200]
or
/ ontrialbegin = [values.fixduration = replace(400, 1600)]
If you run
<values>
/ fixduration = 0
</values>
<trial practice_trial>
/ontrialbegin = [values.fixduration = 400 + round(rand(0,1))*1200]
/ontrialbegin = [trial.practice_trial.insertstimulustime(text.mask, 200+values.fixduration);]
/stimulustimes = [1=fixation_cross_text; 200=practice_text]
/validresponse = (31, 38)
/ ontrialend = [trial.practice_trial.resetstimulusframes(); ]
</trial>
<text fixation_cross_text>
/ items = ("+")
</text>
<text practice_text>
/ items = ("fixduration = <%values.fixduration%>")
</text>
<text mask>
/ items = ("MASK_MASK_MASK")
</text>
<block myblock>
/ trials = [1-4 = practice_trial]
</block>
<data>
/ columns = [trialnum values.fixduration text.mask.stimulusonset]
/ separatefiles = true
</data>
vs
<values>
/ fixduration = 0
</values>
<trial practice_trial>
/ ontrialbegin = [values.fixduration = replace(400, 1600)]
/ontrialbegin = [trial.practice_trial.insertstimulustime(text.mask, 200+values.fixduration);]
/stimulustimes = [1=fixation_cross_text; 200=practice_text]
/validresponse = (31, 38)
/ ontrialend = [trial.practice_trial.resetstimulusframes(); ]
</trial>
<text fixation_cross_text>
/ items = ("+")
</text>
<text practice_text>
/ items = ("fixduration = <%values.fixduration%>")
</text>
<text mask>
/ items = ("MASK_MASK_MASK")
</text>
<block myblock>
/ trials = [1-4 = practice_trial]
</block>
<data>
/ columns = [trialnum values.fixduration text.mask.stimulusonset]
/ separatefiles = true
</data>
and look at the text.mask.stimulusonset column, you should see that the timings are what they are supposed to be in both cases:
1 1600 1799
2 1600 1799
3 400 599
4 400 599
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