Background flicker

Hi guys,

I’m fairly new to PsychoPy3 and try to create my first visual search experiment with the builder. So far so good, I’ve added all the relevant stimuli I need. However, I need to make the background flicker (change rapidly between black and white): In one block, with 10 Hz, in another block, with 20 Hz.

Any ideas how to achieve this? I could only implement uniform backgrounds but no changes.

Best regards and many thanks,