Randomize dot placement


I am using PsychoPy for the first time and am quite new to creating experiments in general. I am trying to create a dot probe task using the Builder view, and I was wondering how I could randomize which image a dot appear behind throughout the study.

For example, if I have 80 trials with 2 images, using the builder view, how can I make a dot appear behind the top image half the time, and behind the bottom image the other half of the time, in a mixed order?

Thank you!


A simple and straightforward way is to use a condition-file. Create a column named ypos. Insert y-coordinates (0.25, -0.25; the actual number will depend on your screen units) in this column. Refer to ypos in stimulus-Property, Position argument (I used a polygon to create a dot). Don’t forget to set set every repeat.


Here is the specification of the loop

It randomizing the condition file, see below, and repeats it five times or 40 trials


So to get 80 trials, you need to set nReps to 10.

BTW, you could specify the images in the condition file as well. But if you use only two images, it it probably not worth the effort.

Best wishes Jens