Welcome! This is Professor Neil McNaughton's Lab's Stop Signal Task (SST) experiment (see the below figure). This SST was created with the intention of being used in conjunction with functional magnetic resonance imaging (fMRI). Information about where in the project different components are scripted can be found in the wiki.
As is standard with SSTs this task can be broken into two types of trials: go trials and stop trials. A single go trial our SST consists of the following steps: a variable inter-trial interval (ITI), a 0.5 s attention stimulus, a 1 s directional stimulus, and a 0.5 s feedback stimulus. The ITI times are a set of values, between 0.5 and 4 s, which were sampled from a logarithmic distribution (t(x) = -ln(x)/λ). While these times will appear random to a participant engaging with the task, they are fixed across all trials.
In the case of stop trials, all of the steps are the same with the exception of the directional stimulus where a stop sound will play some time after the stimulus has been presented. It is the participant's job to refrain from entering a left or right key press when they hear the sound. The time between the onset of the stimuli and the stop sound, known as the stop signal delay (SSD), is drawn from one of three staircase designs.
Figure 2
Menus you will need to navigate in order to add a new parrallel port to
PsychoPy's list of available ports.
The SST is has been created in PsychoPy3 and requires PsychoPy3 2021.1.3 or newer to run (provided PsychoPy's "Use PsychoPy version:" option still works).
Once PsychoPy3 is installed you can open SST.psyexp and run the task. If you
installed a newer version of PsychoPy3 you may need to change the PsychoPy
version being used to run the task. This should be located under:
experiment settings (the gear icon) -> Basic -> Use PsychoPy version.
As stated above, this SST was created with the intention of being used in
conjunction with functional magnetic resonance imaging (fMRI). As such, in
between blocks of trials the task will wait for a keyboard press (= by
default) before continuing the experiment.
Additionally, the left and right response keys are mapped to 2 & 3 for
right handed participants and 7 & 8 for left handed participants.
Ensure your conditions file has been filled out correctly.
The conditions file is used to define the trial blocks and the type of trial
presented to the participant. In particular trials labelled 0 under
TrialTypes will be go trials, while any other integer will be a stop
trials with each number representing a unique staircase. Each block is defined
by a set of repeating integers under the Block header. For example,
1, 1, 1, 2, 2, 2, 3, 3, 3 indicates three blocks: 1, 2, and 3. These integers
must be in ascending order. The BlockType column is used to indicate whether
or not a block is a practise run or not. This is important as practise blocks
will not wait for a = keyboard press to trigger them and will not have stop
trials. To indicated a block as a practise block simply insert the keyword
practice under the BlockType column, next to the first integer in the block.
Any other keyword will be treated as "not-a-practise." So I like to use fMRI.
Finally, the L2R_ratio column is used to indicate the ratio of left stimuli
to right stimuli you would like to appear during each block. Leaving this
column empty will default practise blocks to 0.5 (or a 50:50 split) and
stop blocks to a random ratio.
By default I have left the task with full screen disabled and the Esc key,
which exits the task, available. This is because I assume you'd like to test
the task before using it on participants.
To enable fullscreen you will need to go into the experiment settings and
untick the Enable Escape key tick box in under the Basic tab (see
Figure 3). Likewise, to disable the escape key you will need to go into the
experiment settings and untick the Full-screen window tick box in under the
Screen tab (see Figure 3).
Figure 3
Menus to traverse in order to disable the Escape key and/or enable full
screen.