Go/No Go Task Timing and Accuracy Logging

[katherine]

Hello Everyone,

I would be very grateful if you could help me with a task I am
programming. I am having a problem with a Stop Signal (Go-NoGo) Task.

This task has two conditions - Go (with two stimuli: < and >) and No
Go (Stop Trial) (also with stimuli: < and >). Each trial is timed to a
trigger from our scanner, which comes every 2.8 seconds. Each trial
lasts for two trigger periods (5.6 seconds). The Go condition is
working fine. The subject sees a "ready" crosshair for 500ms, then has
900ms to respond to a stimulus prior to a feedback slide. In the Stop
condition the subject sees a "ready" crosshair for 500ms, sees a
stimulus, and hears a beep ("sound delay") shortly after the
presentation of the stimulus, which cues them to inhibit their
response. The timing of the presentation of the beep is dependent upon
a staircase. As the accuracy of the subject's responses on the Stop
Trials increases the time between the presentation of the stimuli and
beep should also increase. As accuracy decreases, the time should also
decrease. The goal is to keep the subject's accuracy around 50%. At
the beginning of the task the experimenter enters the starting time of
the beep presentation, based on the ending time from the subjects
practice run (hopefully already close to 50%).

I am having two problems with the script as it currently stands.
First, I am trying to set up the No Go portion (Stop Trial) of the
task so that it lasts for two trigger periods. Currently, if a subject
mistakenly responds on a No Go trial the "TrialBlankEnd2" display is
skipped. "TrialBlankEnd2" is a blank 1200ms display which is used to
lengthen the duration of the trial in order to ensure the trial lasts
for two trigger periods. If ""  is skipped the next trial starts after
only one trigger period.

I tried to achieve the same effct by using a "sleep" command, using
the following code:

c.SetAttrib "StimSlide2.ACC", StimSlide2.ACC
If StimSlide2.ACC = 0 Then
sleep (1300)
End If

I tried to insert this code in an inline file after "sound delay," but
it seems that when this code is implemented StimSlide2.ACC is always
set to zero, instead of set to 1 (which it should be set to when the
person correctly inhibits) The result is that the staircases I've set
up do not work.

What I'm looking for is a way to ensure that no matter what the
subject's response on a Stop Trial, the next trial does not start
until two trigger periods have elasped (5.6sec). If "TrialBlankEnd2"
is skipped, the next trial starts after one trigger period (2.8sec).
If I use a sleep command, it seems to throw off the accuracy count (on
which the staircasing is dependent).

It seems as though the script is set up correctly for the most part.
The staircases do work when the accuracy count works. Is there a
better way to set up The Stop trials that will ensure that the trials
have "blank time" on the end and that the accuracy counts are
accurate?

Thank you very much for your help with this. I appreciate it.

Katherine Koenig
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