randomising the nth image in a sequence

[Michiel Spape]

Hi Victor, Lois & List,
Just to suggest another way for those who do not like inlines:
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. 

Thanks to Elkan Akyürek (http://www.psy.uni-muenchen.de/exp/ma/akyurek/publications/mainColumnParagraphs/012/document/Akyurek_Hommel_2005_MemCog.pdf) who taught me this trick 5 years ago as an easy way to programme an attentional blink (see link). Notice it has a few nice advantages: there are no distracter repetitions, there's an equal number of trials in which the 6th is target, etc.
Best,
Mich

Michiel Spapé
Research Fellow
Perception & Action group
University of Nottingham
School of Psychology


-----Original Message-----
From: e-prime at googlegroups.com [mailto:e-prime at googlegroups.com] On Behalf Of Victor
Sent: 15 July 2009 13:26
To: E-Prime
Subject: Re: randomising the nth image in a sequence


Hi Lois,

There may be other ways to do this but I might suggest declaring a
global variable, say Dim imagesequence as integer and then at the
beginning of a list, determine the variable as imagesequence = random
(5,8) in an inline in order to get a random number between 5 and 8.

You can then have another variable, say Dim  trialcount as integer
which increases (trialcount = trailcount + 1) after each stimlus
presentation. Also declare a variable Dim oddimage as string for the
odd image. It is then possible to have an inline before the stimulus
presnetation to say

If imagesequence = trialcount then oddimage = "file.bmp"
c.setattrib "imagevariable", oddimage

This should change the image is changed to the odd one on the
specified trial.

Hope this helps,
Tim

On Jul 14, 11:09 am, Lois <doro... at googlemail.com> wrote:
> Hi, I'd like to display a sequence of 9 images in which only the 5th,
> 6th, 7th, or 8th will be different to the rest of the sequence. This
> sequence will be used in around 72 trials, in which the odd image in
> the 5th, 6th etc. position will be randomised.
>
> Would anyone have a suggestion of the best way to do this please?
>
> Thanks,
> Lois


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