Short duration stimulus displayed on background

I have an experiment with different backgrounds in each block. I need the background to be visible for the entire duration of the block. At various times, a small target stimulus appears on the screen for 1 sec. I’m having 2 problems:

  1. I cannot change the location of the target stimulus. I try to select variable, but as soon as I exit the tab, it defaults back to fixed;
  2. when the target stimulus is removed, it leaves behind a white box. I’m assuming this has something to do with the format of the file for the target stimulus. I have tried everything I know to remove anything in the background of stimulus file, but I still get the white box.

Can anyone help?

Thanks so much.

Is the background a solid color or an image?

The background is another picture file

I am trying to put them in two different events, so I can use a list to pull the targets for the second stimulus, and still keep the same background for all the other events in that block.

This would be faster handled using screen sharing. Please send me an email to setup a time.

Do you have time now?
My email is
I can be available anytime tonight, or Wednesday after 1 (Central Time Zone)

I replied by email. Tomorrow works.