Adaptive Method in Eprime

[PinkSunflower]

I appreciate your help, David. The thing is: I have no clue where to
start here. I'm just starting to find out how to draw a line in
Eprime. Therefore, your sketch - which sounds highly professional - is
hard to understand for me. ;-)

But I'd like to thank you for your time.

Greetings,
CAROLINA

On Feb 8, 5:06 pm, David McFarlane <mcfar... at msu.edu> wrote:
> Carolina,
>
> >Participants in my study will see two lines: One line is the standard
> >line; it never changes its length. The other one is the comparative
> >line: The comparative line changes its size depending on the response
> >of the participants on the trial before. The length of the line is
> >calculated by an algorithm that looks like this: Xn+1 = Xn - c/n (Zn -
> >K). Xn is the actual stimulus size of the comparative line, c is a
> >constant, n is the trial number, Zn is the response of the participant
> >which is either 0 or 1 and K is a set criteria. After every trial Xn+1
> >is calculated and set as the new stimulus size Xn. This new stimuli
> >size should be displayed in the next trial. This continues until a
> >criteria is achieved.
>
> I programmed something very much like this last year, a temporal
> acuity experiment where the duration of a tone was modified after
> each response according to a "staircase" procedure.  Here's an
> outline of what I did.
>
> The essential structure looks like this:
> StaircaseInitScript
> TrialList
>      TrialProc
>          TrialInitScript
>          StimulusObject
>
> TrialList just provides a looping mechanism for running the trials,
> and allows you to put an upper limit on the number of
> trials.  TrialProc runs each trial within a
> staircase.  StimulusObject shows your lines and collects a
> response.  Now, your trials may include more elements (fixation,
> mask, a separate response object), but you get the idea.
>
> The stimulus is controlled by using an attribute reference in the
> relevant property of your stimulus object.  In your case it will be
> line length, so we might enter this as [LineLength].
>
> The value of LineLength does not come from a list, but instead from
> an inline script, TrialInitScript.  That is the key.  TrialInitScript
> does all the work of looking at the previous response and calculating
> the next value of LineLength using whatever computation you like.  I
> can't go into much detail here, but it will probably involve some
> If... Thens, etc.  Three things you will need to know,  (1) You can
> get the subject's response with StimulusObject.RESP.  (2) You set
> LineLength in script like this:  c.SetAttrib "LineLength", x  (where
> x is some variable; and that variable can itself be named LineLength
> without conflict).  (3) When the subject meets criterion you exit the
> list like this:  TrialList.Terminate.
>
> Finally, all this staircase stuff has to be initialized somewhere,
> that's what StaricaseInitScript is for.  You will also need some
> global variables, so some stuff will go in the User area of the full
> experiment script.  And if you want to run several staircases you
> will need to enclose all this in yet another list, e.g., StaircaseList.
>
> Again, this is only a sketch, if I tell you any more I would have to
> charge you :).
>
> -- David McFarlane, Systems Designer
>     Dept. Psychology, Michigan State University
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