3 questions

[David McFarlane]

Raúl,

>1: I would like to know how in an experiment 
>such as STROOP, I can stop it at a determined 
>point in time (such as in the paper-pencil 
>version), and not for a specific amount of 
>trials such as is normally done by computer.

Do you just have your trials in a List object, 
and want to run that list for a given time?  In 
that case, just go to the property pages for the 
list, go to the Reset/Exit tab, and under Exit 
List put in a number of seconds (anything from 0 
to 32767).  The list will then run as many samples as it can in that time.

If you have something else in mind, you would 
have to run some inline script with Clock.Read.

>2: I would also like to know if it is possible 
>to develop an experiment where the requirement 
>is to have a specified percentage of success 
>(and/or response speed) that allows the subject 
>to go to the next phase. It could be from a 
>trial phase to the evaluation phase.

I believe this has been discussed & answered 
before, but I don't have the link offhand.  But here is a rough sketch.

First, define some global variables to keep track 
of # of trials, # of successes, etc. (see 
sections 4.3.5 and 4.4.3 in the E-Prime User's 
Guide).  While you're at it, it would be best to 
define some constants instead of using "magic 
numbers" in script later.  Something like:

Const  SuccessCriterion as Single = 0.75  ' 75% correct
Dim  NTrial as Integer
Dim  NSuccess as Integer

Then, add some inline script to your procedure to 
accumulate statistics and test for success, etc., something like:

NTrial = NTrial + 1
If Probe.ACC Then NSuccess = NSuccess + 1
If (NSuccess / NTrial) > SuccessCriterion  Then
    do_something
End If

where do_something might be a simple Goto, or an 
Exit For, or an Exit Do, or a List.Terminate (my 
own favorite), depending on how you have structured your program.

Again, this is just a rough sketch, you will have 
to work out the specifics for your experiment.

>3: Finally, is it possible to program within the 
>same block of trials one trial that has (for 
>example) 2 presentation stimuli, four updates 
>and two questions and that the next has 2 
>presentation stimuli, 3 updates and two questions... and so on and so forth

Yes.  Each level (row) of a List can have its own 
Procedure, in fact you can have a list that runs 
a different procedure for every level, so you can 
have each trial of a block do something completely different.

-- David McFarlane, Professional Faultfinder


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