How to avoid presenting targets consecutively
Tobias
tobias.fw at gmail.com
Fri Jul 22 14:06:19 UTC 2011
I have a similar problem. In a visual search experiment, I have four
target types and it happens often that one of them is used 10 times in
a row. Let's not discuss how random E-Primes "random" is (I don't
really trust it!).
But: How can I implement a pseudorandom selection from a list? Let's
say I want E-Prime to choose randomly trials from a list, but one of
the four target types must not be repeated more than twice in a row.
I see your answers here, but I think we have to tell apart two things
here: No repitition of stimuli within a trial (e.g. attentional blink)
on one side and no repition from trial to trial (e.g. two target types
in visual search) on the other side.
Michiel's solution works perfectly for the former case I think. But I
don't see any way of implementing that for my case. Micah's solution
might be a good idea, but it is not very handy if you want a different
random order of trials for each subject.
I guess it would be best if there is a way to make this in code. For
example, E-Prime could record the recent trial types:
target_t1 = target_t2
target_t2 = c.getattrib("targettype")
and then, E-Prime could check each new trial for repition:
if c.getattrib("targettype")=target_t1 or
c.getattrib("targettype")=target_t2 then "draw new trial".
Unfortunately there is no command "draw new trials"
That would be my way to go. Any hints?
On 22 Jul., 11:02, Michiel Spape <Michiel.Sp... at nottingham.ac.uk>
wrote:
> Hi all,
> Pseudo- (or actually offline) randomisation, would work depending on the task and duration (if indeed fMRI, I'd go for that - but EEG with hundreds of trials, not so much). Another answer may be found inspired in an old trick for programming an attentional blink (see my post here:http://www.google.co.uk/url?sa=t&source=web&cd=4&ved=0CDoQFjAD&url=ht...)
>
> Outtake:
> -----------
> If the image-sequence is a procedure in a blocklist, make that something like
> (start procedure)-->imagedisplay1-->imagedisplay2-->...-->imagedisplay9
> Let the blocklist have 9 attributes: "imagefile1", "imagefile2",.., "imagefile9", and two nested lists: distracters and targets, set them both to randomise. Give them both an attribute, respectively "distracter" and "target". Fill these attributes with all the targets and distracters you like. Let these lists randomise.
> Set the filename properties of the 9 imagedisplays to [imagefile1], [imagefile2], .., [imagefile9].
> Set the attributes of imagefile1 to 9 (i.e. in the blocklist) to
> [distracter:1]
> [distracter:2]
> [distracter:3]
> [distracter:4]
> [distracter:5]
> [target:1]
> [distracter:6]
> [distracter:7]
> [distracter:8]
>
> For a trial sequence in which the 6th display is the different (i.e. target, odd) picture. Obviously, you need two more lines, for the other 7th or 8th image to be the target.
> ----------------
>
> Given that you want something like distractor/distractor/distractor/target/distractor... etc, it may well be best to programme your experiment such that rather than having a "target" trial, you have a number of slides (or whatnots) after another in a single trial. You can then make your list so that sequences are randomised between trials, rather than trials themselves. So, if I have a list like:
> Slide1Word,Slide2Word,Slide3Word,Slide4Word
> [Distractor:1],[Target:1],[Distractor:2],Target:2],[Distractor:3]
> [Distractor:1],[Target:1],[Distractor:2],[Distractor:3],[Target:2]
> [Distractor:1],[Distractor:2],[Target1],[Distractor:3],[Target:2]
> ...
> And the list randomises between these 3 sequences, 1) there's no way that two targets can come after another, 2) targets/distractors are randomised and 3) orders are randomised to a very safe degree (since it's unlikely that for one participant, for example, all targets will come relatively to the end).
> Hope that helps.
> Best,
> Mich
>
> Michiel Spapé
> Research Fellow
> Perception & Action group
> University of Nottingham
> School of Psychologywww.cognitology.eu
>
> -----Original Message-----
> From: e-prime at googlegroups.com [mailto:e-prime at googlegroups.com] On Behalf Of David McFarlane
> Sent: 21 July 2011 22:05
> To: e-prime at googlegroups.com
> Subject: Re: How to avoid presenting targets consecutively
>
> 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 athttp://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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