OS (e.g. Win10). PsychoPy version (e.g. 2025.1.1 Py 3.8).
Hi everyone,
I am designing an EEG experiment in PsychoPy and would appreciate some guidance on implementing counterbalancing efficiently. I have added the image here.
Each trial contains target faces:
An emotional face (happy, angry, or neutral).
Its corresponding Fourier phase-scrambled image of the face (control stimulus).
The target face appeared either at the center of the screen (foveal display condition) or to the left or the right (50 % on each side as peripheral conditions).
The presentation conditions are counterbalanced such that:
In some trials, the emotional face is presented centrally while the Fourier phase-scrambled image appears in the left or right visual field as shown in the image.
In other trials, the Fourier phase-scrambled image is presented in the opposite side of peripheral target face (i.e., left visual field, if the target face was on the right, and vice versa).
The peripheral stimulus should also be counterbalanced across the left and right visual fields.
The experiment consists of five blocks, and I would like the central/peripheral presentation order to be balanced across blocks and across participants.
I have a one question:
How should I keep both central and peripheral target faces trials within the same blocks and counterbalanced?
Since this is an EEG experiment, maintaining precise stimulus timing is essential, so I would prefer a Builder-compatible solution that preserves timing accuracy.
Counterbalancing trial types is normally done by creating a spreadsheet with all possible combinations of the key variables.
Emotional face centre (25% with scrambled left, 25% with scrambled right), left (25%), right (25%)
That seems to be just four trial types. Is the issue that you would like the actual faces used to be randomised independently? If so, have a look at my independent randomisation demo.
PV block1.xlsx (12.5 KB)
hi, to follow up further on my doubt: i have attached two of my excel sheets here, the primary question is that in my task there are going to be two conditions : central and peripheral (no more) now how exactly am i supposed to design my excel sheets for a total of 360 trials wherein there would be 180 trials corresponding to central presentation (including target always in center and scrambled faces either on left or on right) and 180 trials for peripheral presentation (including both left and right presentation of target and scrambled faces) (note: please refer to the image attached above in my query to exactly understand the visualization of my paradigm) Now: question 1. The excel sheets that i have attached are they correctly designed ? 2. now from the center, the peripheral presentation would happen at 10 degree or so (imperfect numbers right now)and central presentation would happen with target face always at the center and scrambled face on either left or right, SO HOW AM I EXACTLY SUPPOSED TO INCORPORATE DIFFERENT DEGREES IN SIMILAR BLOCK? COUNTER BALANCING CAN BE EVENTUALLY TAKEN CARE OF: BUT PRIMARILY I REALLY NEED TO UNDERSTAND HOW TO GO ABOUT THE EXCEL SHEET DESIGNING AND DIFFERENT DEGREES OF PRESNETATION IN The SAME BLOCK (THIS EXPERIMENT IS BEING DESIGNED ON PSYCHOPY BUILDER) .
I have also attached the existing design of my experiment on psychopy builder, so far we were running experiment only with peripheral presentation of stimuli as the condition and now we are trying to include central vision as well-hence the above questions!
It is often better to start with a small set of conditions to construct the counterbalancing, and then expand this to cover the full material set. I hope that I have understood our design correctly. Here is my example for a condition file.
target_face
scrambled_face
place_target
place_scrambled
block
emo1
scrambled1
central
left
1
emo2
scrambled2
central
left
1
emo3
scrambled3
central
right
1
emo4
scrambled4
central
right
1
emo5
scrambled5
left
right
1
emo6
scrambled6
left
right
1
emo7
scrambled7
right
left
1
emo8
scrambled8
right
left
1
There are eight target faces (emo1–emo8) and eight scrambled faces (scramble1–scramble8). The target faces appear in a central position in 50% of cases and in a peripheral position (25% on the left and 25% on the right) in the other 50%. The scrambled faces appear an equal number of times on either side of the target face.
place_target and place_scrambled determine the presentation position.
That design, while simpler, will confound face with condition, which is why I recommended independent randomisation. Maybe that isn’t important for this study of course.
Yes, my design confounds face and condition. I should have made this clearer. This could be countered using a Latin square design or independent randomisation.
