Hi,

I have a task where people respond to types of stimuli (ex. happy trials, sad trials).  I want to be able to get the mean latencies for each trial type, but separately get the latencies for just the correct trials and for just he incorrect trials (so I'd end up with Happy_correctmeanlatency, Happy_incorrectmeanlatency, Sad_correctmeanlatency, Sad_incorrectmeanlatency, etc).

I was thinking I could use /onblockend and some if statements to calculate the latencies for each, but I'm getting confused on exactly how to do it.

Would it be...

/onblockend =
  [if (trial.Happy.correct == true)
  values.Happy_correctmeanlatency = meanlatency(Happy)]
/onblockend =
  [if (trial.Happy.correct == false)
  values.Happy_incorrectmeanlatency = meanlatency(Happy)]

...and then repeat for other trial types in the block? 

No. You need two <values> entries per trial-type: One where you aggregate the sum of correct latencies, one where you count the number of correct responses. You need to update these values /ontrialend. You then calculate the mean via an <expression>, simply dividing the sum by the number of correct responses.

<values>
/ a_sumlatency = 0
/ b_sumlatency = 0
/ a_ncorrect = 0
/ b_ncorrect = 0
</values>

<expressions>
/ a_meanlat_correct = (values.a_sumlatency/values.a_ncorrect)
/ b_meanlat_correct = (values.b_sumlatency/values.b_ncorrect)
</expressions>

<expt>
/ postinstructions = (performance)
/ blocks = [1=myblock]
</expt>

<block myblock>
/ trials = [1-10 = noreplace(a,b)]
</block>

<trial a>
/ ontrialend = [if (trial.a.correct) {values.a_sumlatency += trial.a.latency; values.a_ncorrect += 1}]
/ stimulusframes = [1=atxt]
/ validresponse = ("a", "b")
/ correctresponse = ("a")
</trial>

<trial b>
/ ontrialend = [if (trial.b.correct) {values.b_sumlatency += trial.b.latency; values.b_ncorrect += 1}]
/ stimulusframes = [1=btxt]
/ validresponse = ("a", "b")
/ correctresponse = ("b")
</trial>


<text atxt>
/ items = ("The correct response is A")
/ txcolor = red
</text>

<text atxt>
/ items = ("The correct response is B")
/ txcolor = blue
</text>

<data>
/ columns = [date time subject group blocknum blockcode trialnum trialcode stimulusitem response latency correct values.a_ncorrect values.a_sumlatency values.b_ncorrect values.b_sumlatency expressions.a_meanlat_correct expressions.b_meanlat_correct]
/ separatefiles = true
</data>

Thanks, Dave.  This will give me the mean latencies for the various trial types for correct trials.  Is there a way to also get the latencies for the incorrect trials?