terminate a list using a button release (trials consist of trains of brief stimuli)

[Devin Terhune]

Hi. 

We are having some difficulty with a temporal reproduction task. A trial in 
our task consists of a series of very brief circles (each 1 frame, so 
around 13.3ms). Participants press (and hold) a button in response to a 
blank screen and the train of circles is presented. When they release the 
button, we want to terminate the list controlling the train of circles. We 
are interested in recording the duration that the button was held.

Please note that we can easily do this if the stimulus during the button 
press is a constant circle. Our problems emerge because of the 
rapidly-changing stimuli.

At the moment, we've done the following:

we have set up an InLine which directly follows an image (circle) display 
[called ReproductionStim] with the following command:
 
"If ReproductionStim.RT > 0 then List.Terminate"
 
where, ReproductionStim.RT is the response time measure of the *release *of 
the button and List is the name of the list we are trying to terminate (the 
train of circles).

The task works most of the time if the circles are 100ms in duration 
(each), but even in this version on a small percentage (<10%) of trials, 
the button release does not terminate the list. However, when we decrease 
the durations to 13.3ms (or slightly longer), the list is not terminated 
and the release of the button is not reliably recorded.

Based on this, we believe that E-prime requires a longer stimulus 
presentation to be able to register the release of a button. It is possible 
that our inline is incorrect however.

Any thoughts on this - and in particular whether it should be possible - 
would be great. If it's not possible, we'll have to try something else.

Thanks for any comments/suggestions!

cheers, Devin 
 

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