How to avoid presenting targets consecutively

[David McFarlane]

Micah,

Great answer.  I often get so wrapped up in looking for sophisticated 
automated solutions that I overlook the simple ones, and what you 
recommend is exactly what we do for fMRI in order to avoid problems 
with accidental multicollinearity (which flusters correlation & 
deconvolution analyses).  And as it turns out, this answer also 
appeared in a discussion at 
http://support.pstnet.com/forum/Topic3166-5-1.aspx .

-- David McFarlane, Professional Faultfinder


>Just as a general comment, and certainly not the best solution:
>
>I generally do my stimulus randomizations outside of e-prime. It's
>much easier to specific a pseudo-random or fully random sequence of
>stimuli outside of e-prime (in excel for example) and to then import
>it into one triallist that is sequentially sampled. This way you can
>randomize the list while keeping a look out for exactly the kinds of
>problem you mention.
>
>Hope that helps,
>Micah
>
>Mark A wrote:
> > Dear E-Prime group,
> > I am fairly new to E-Prime, but thus far have found online discussions
> > within the group, as well as PST instructions and examples that have
> > allowed me to program everything required, with one exception. The
> > experimental task is simple: A participant listens to a series of
> > words and presses a button whenever a particular word is heard (i.e.,
> > the target word, "apple" in the example below). The target word is
> > presented 4 times.
> >
> > My problem is this: I wish to present a series of stimuli (.wav files)
> > randomly, with the restriction that I do not want "Target" files to be
> > presented consecutively. Rather, I want them to be separated by at
> > least one distractor (or non-target).
> >
> > To illustrate, this is an excerpt from one of my lists:
> >
> > 
> Weight        Nested  Procedure       Sound           Talker  Target  SoundDur
> > 
> 1                             MAppleTrial     m1apple.wav     m1 
>            yes             422
> > 
> 1                             MAppleTrial     f4apple.wav     f4 
>            yes             546
> > 
> 1                             MAppleTrial     m1apple.wav     m1 
>            yes             422
> > 
> 1                             MAppleTrial     f4apple.wav     f4 
>            yes             546
> > 
> 1                             MAppleTrial     m2bear.wav      m2 
>            no              332
> > 
> 1                             MAppleTrial     f3bin.wav       f3 
>            no              375
> > 
> 1                             MAppleTrial     m3cat.wav 
>    m3              no              383
> > 
> 1                             MAppleTrial     f2chalk.wav     f2 
>            no              586
> > ..... and so forth (there are 4 targets and 23 distractors).
> >
> > Currently, I have the list set to "Random", however, this does not
> > guarantee that the Target files (top 4 rows) will not occur
> > consecutively. I think that the solution will involve a conditional
> > statement (perhaps using In line) comparing whether the previous file
> > presented was a target, but I am unsure how to implement this.
> >
> > An additional consideration is what to do if there are only 2 cycles
> > left, and the two files left are both target files. If this is very
> > hard to avoid, I am willing to live with this, as it is unlikely to
> > occur very often. Any tips or links to helpful discussions on similar
> > topics will be very much appreciated.

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