Millisecond Forums

I am not sure what exactly "contingency positive/negative words" is supposed to mean in this particular context. Please clarify / explain what you want to do in sufficient detail.

Similarly, I am unable to figure out if / how "each block consists of 80 trials + 8 incongruent trials" relates to the above. Please clarify that also, especially what "incongruent trials" is supposed to mean in this context.

I will specify the experiment.


Condition 1:
In each block, participants are randomly presented with 40 positive words (printed in blue) and 40 negative words (printed in green). They are instructed to click on "Positive" when a green word is presented and on "Negative" when a blue word is presented. However, on 4 trials a positive word is printed in blue instead of green(= catch trial) and on 4 trials a negative word is printed in green instead of blue(= test trial).

Condition 2:
Same as condition 1, however, this time it's all reversed. That is, participants are instructed to click on "Positive" when a blue word is presented and on "Negative" when a green word is presented. However, on 4 trials a positive word is printed in green instead of blue (= catch trial) and on 4 trials a negative word is printed in blue instead of green (= test trial).

Sorry, I'm still unclear. You state (under Condition 1), participants are presented with

"40 positive words (printed in blue)" and "40 negative words (printed in green)". I take it those are your "regular contingency" trials. You then go on to define a catch trial as " a positive word is printed in blue ... (= catch trial)" and a target trial as " a negative word is printed in green ... (=target trial)".

I am unable to discover any difference between your regular trials and your respective catch / target trials. In all cases positive words are displayed in blue and negative words in green according to your description.

Sorry, that's indeed incorrect. I meant the following: 40 positive words are printed in blue, the other 40 negative words are printed in green. Participants have to respond to blue words by clicking on "Positive" and to green words by clicking on "Negative". In addition, 4 positive words are printed in green and 4 negative words in blue.

Then you should be able to simply set up a total of four <trial> elements -- one displaying a positive word in blue, one displaying a positive word in green, one displaying a negative word in green, one displaying a negative word in blue -- and sample from those trial elements in the desired proportions (the latter can be efficiently expressed via <list> elements). In a nutshell:

<expt>
/ blocks = [1=c1block]
/ subjects = (1 of 2)
/ groupassignment = groupnumber
</expt>

<expt>
/ blocks = [1=c2block]
/ subjects = (2 of 2)
/ groupassignment = groupnumber
</expt>

<block c1block>
/ trials = [1-88=list.c1triallist]
</block>

<block c2block>
/ trials = [1-88=list.c2triallist]
</block>

<list c1triallist>
/ items = (trial.pos_blue, trial.neg_green, trial.pos_green, trial.neg_blue)
/ poolsize = 88
/ itemprobabilities = [.45; .45; .05; .05;]
</list>

<list c2triallist>
/ items = (trial.pos_blue, trial.neg_green, trial.pos_green, trial.neg_blue)
/ poolsize = 88
/ itemprobabilities = [.05; .05; .45; .45;]
</list>

<trial pos_blue>
/ trialduration = 10
</trial>

<trial pos_green>
/ trialduration = 10
</trial>

<trial neg_blue>
/ trialduration = 10
</trial>

<trial neg_green>
/ trialduration = 10
</trial>