probabilistic stimuli

[David McFarlane]

One way to do this, maybe some others will come up with alternatives...

Suppose your stimulus is named StimText, and you use an attribute 
reference, "[FollowupImageFile]", for the image file in the following 
stimulus.  Then in inline code after StimText and before your 
followup stimulus, do something like the following:

     If (StimText.ACC And (PRNG.GetNext() < 0.8)) Then
         c.SetAttrib "FollowupImageFile", "CorrectFollowupImageFile"
     Else
         c.SetAttrib "FollowupImageFile", "OtherFollowupImageFile"
     End If

See the PRNG and related topics in the E-Basic Help facility.

BTW, the comparison "< 0.8" will work for all practical purposes, but 
you might consider whether "<= 0.8" would be more canonically correct 
-- I leave that as an exercise to the reader.

-----
David McFarlane
E-Prime training 
online:  http://psychology.msu.edu/Workshops_Courses/eprime.aspx
Twitter:  @EPrimeMaster (https://twitter.com/EPrimeMaster )

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At 10/23/2013 12:55 PM Wednesday, Pauline FAVRE wrote:
>Dear E-prime users,
>I try to control the occurrence of the a stimulus, i.e., during the 
>experiment, each trial consist first of a presentation of a stimulus 
>and then I would like that another image appears for only 80% of 
>correct responses on the previous stimulus (and different images for 
>the remaining 20% and the incorrect responses).
>
>In summary, I just would like that a specific stimuli appears in 80 
>% of the cases.
>
>Is there an inline script that permit that a stimuli appears only in 
>a determined percentage of trials?
>
>Thank you very much for your help!

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