adjusting time of stimulus presentation by key presses

[David McFarlane]

Stock reminder:  1) I do not work for PST.  2) PST's trained staff 
takes any and all questions at 
http://support.pstnet.com/e%2Dprime/support/login.asp , and they 
strive to respond to all requests in 24-48 hours -- this is pretty 
much their substitute for proper documentation, so make full use of 
it.  3) If you do get an answer from PST Web Support, please extend 
the courtesy of posting their reply back here for the sake of others.

That said, here is my take...

First, it is very possible to make such a task in E-Prime, though it 
will not be simple.  In short, you could use an attribute reference 
for the Duration property of each stimulus, and then adjust that 
attribute value in inline code using c.SetAttrib (see Chapter 4 of 
the User's Guide that came with E-Prime, and the "Context" topic in 
the online E-Basic Help).  You will also need some global variables 
to keep track of things, once again see Chapter 4.  To use "up" & 
"down" key responses you will have to use the {key} nomenclature, see 
that topic in the online E-Basic Help.  You might also want to learn 
about using releases as responses in case you want to do things by 
having subjects press & hold a key, etc.  To create your graphics, 
you might use another attrbute reference to set the Height or Width 
property of objects on a Slide (my own favorite trick), or delve 
right into the Canvas object and draw whatever you like.

I leave the rest as an exercise for you.

-- David McFarlane, Professional Faultfinder


>I would like to develop a task in which the default viewing time of
>each stimulus could be adjusted by the participants according to their
>'work-effort', i.e. the frequency of key-pressing of either the 'up'
>or the 'down' keys. I would like to have a visual analogue scale
>presented together with each stimulus which would provide participants
>with a real time indication of the viewing time duration, with a bar
>moving downwards over time (the speed of movement could either be
>slowed or increased by the key presses).
>
>First of all, is it possible to create such a task with E-Prime. If
>yes, could anyone please advise on which objects/functions to tamper
>with?
>
>All kinds of input will be very much appreciated!
>
>Cheers,
>A.

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