In my experiment, I draw single letters/symbols in the center of the screen and alternate between them and a fixation dot. I noticed that while the fixation dot is nicely centered, the symbols/letters are not (always). For instance, a capital O or a + sign are, but a small x and a - are not. They appear slightly below the center of the screen. Keyword center is always on default (True) and x and y coordinates are the same between all stimuli (0,0). Is this because text/fonts are drawn as a picture with a dedicated area large enough to fit capitalized as well as small letters?
Either way, is there a way to make sure they are always properly centered without messing around with the x,y coordinates?