This tutorial will walk you through creation of a full experiment to test the Stroop effect (Stroop, 1935) . This example will be based on Experiment 2, where stimulus conflict-words and color patches are presented in random order. The task requires participants to name the color of each stimulus (i.e. the color of the word's "ink" or of the color patch), ignoring the color names spelled out by the words themselves.
Tip: Throughout the tutorial there will be links to other documentation to explain concepts in detail. If you follow a link you can return to this tutorial by hitting the back button in your browser. Alternatively, you can right-click a link and open it in a new tab.
At the end of this tutorial you will have covered the following concepts:
One-factor, three-level experiment using randomly blended stimuli (color-word and color-patch). When presented, each color-word will have a random font color applied.
Newas the creation option.
Incongruentwith a description such as
ink color is different from the color referred to by the word
Congruentwith the description such as
ink color is the same as the color referred to by the word
Neutralwith the description
stimuli in which only a color-patch is displayed
Stimulitab in the study tab bar to go to the stimulus manager and then create a new stimulus set and call it
Componentsin the stimulus set tree and add a new group called
colorwith the component group type
colorgroup by clicking on its name in the table or in the stimulus set tree.
wordwith the component type
patchwith the component type
At this point, you have created a blended component group (
color) containing two groups to be blended (
patch). By default, blending strategy is set to
random and that's how we'll leave it for this exercise. Your stimulus set tree should now look like this (Figure 1).
wordgroup by clicking on its name in the table or in the stimulus set tree.
Create a CSV file containing your color words making sure to
wrap each item in a variable called
ink-color, then import the CSV file. For convenience, you can download one I prepared earlier. The CSV file should look like this (Figure 2).
Once imported, the
word group should look like this (Figure 3).
Note the items are highlighted red as something isn't right. Hovering the mouse over the list will show a detailed explanation of how to fix things. In this case, we are yet to create our
ink-color variable, so let's go ahead and do that now.
Create a CSV file containing your
ink-color variable then import the CSV file by clicking Import variables. For convenience, you can download one I prepared earlier. The CSV file should look like this (Figure 4).
Once your variables have been imported you should end up with something like this (Figure 5).
We have now completed building the color-word items of our stimuli. Now it's time to build our color-patches.
We have now finished building our stimuli resulting in a randomly blended group of color-words and color-patches. A random font color will be applied to each color-word via the
ink-color variable whose strategy is set to
Exclusive to ensure each variable value is used only once per stimulus cycle.
Studyin the study tab bar to go to the study screen and then navigate to the
Study sequenceby clicking on it in the study tree.
Trial block, choose
Newas the creation option and then navigate to it by clicking on its name in the table or in the study tree.
Newas the creation option and then navigate to it. This is the trials timeline.
Existing sets(this is the stimulus set we created earlier).
Stimulus componentand choosing
color(this is the stimulus component we created earlier).
Response - keyboard, choosing
Newand naming it
keysitem in the trials timeline to add keys and values to the response. You are now in edit mode.
Newand naming it
fixationitem in the trials timeline to enter edit mode, set the
Timeout (ms)to 100 and set the fixation
ISI, setting the
Start time (ms)to 100 and setting the
Timeout (ms)to 100.
keys to start after
ISI by setting their
Start time (ms) to 200.
The top-to-bottom order of items on the timeline doesn't reflect their timing order, so if you'd prefer, you can reorder the items by dragging and dropping them until you have something like this (Figure 6).
We have now finished building our trials timeline.
Screenin the trials tab bar.
fixationto the screen by hovering the mouse over the top of the grid and selecting the cell and then selecting
fixationfrom the Insert item list.
Select the 200ms interval on the screen timeline and add
color to the screen using the same method you used to add
fixation in the previous step.
In the trials timeline click on
color and change the font size to 64px using the rich text editor provided.
We have now finished building our trials screen.
Logicin the trials tab bar.
Add the rules shown in (Figure 7).
As shown above in (Figure 7), we have made the following assertions:
false. This means that if no other rule for correctness matches for this trial, the response (including no response) is deemed to be incorrect. This type of rule is referred to as an assignment.
Incongruentif its level is not
Neutral. This means that if no other rule for level matches for this trial, the level is deemed to be
Incongruent(where it was not already
Neutral). This type of rule is referred to as a conditional.
Congruentif both the
wordare the same.
trueif the key pressed (response) is the key that corresponds to either the
We have now finished building our trials logic, and with that, our experiment design is complete.
Although our experiment design is complete, it's not very friendly, so let's fix that.
Trial blockusing the study tree and add new instructions, name it
Newas the creation option.
Instructionsto the top position in the trial block table to make it appear before
Add some introductory text (Figure 8).
Response - keyboard,
Newas the creation option and name it
keyand add a new key. Press the Space bar to add the space key, set the value to anything you like (e.g.
next), then hit Add to add the key and then hit Save to exit edit mode.
Study sequenceand add new instructions, name it
Thankyou messageand choose
Newas the creation option. Navigate to it and write a lovely thankyou message, including some instructions about the keyboard, such as
Hit the space bar to end the study
Add a keyboard response to your thankyou message. We can save ourselves some work by copying a keyboard we created earlier. Click New response, select
Response - keyboard, select
Copy as the creation option, select
key (the keyboard we created in earlier instructions) and name it
key. Note: The last screen in your study must include a buttons response or a keyboard response to end the study. Set the response
Go to next study item or trial.
You now have a fully functional experiment with advanced stimulus generation. Hit Preview study and try it out! To activate the study and allow participants to take part, hit the
Distribution tab in the study tab bar. To download results, hit the
Results tab in the study tab bar.