After I updated my macbook pro to the newest Yosemite software (which I really regret because my mac is now running soooo slow ), I have experienced that
small black boxes flicker whenever I am editing pictures/using brush tools in Photoshop.
I have heard that the same problem happen some time ago with the macbook air but now it is happening to me! I have tried to turn down the Graphic Processor from "Advanced" to "normal" but did not help.
What can I do? I am going crazy seen those boxes flicker every 5 seconds!
Yosemite still has a substantial numbers of bugs that Apple has to fix, especially graphics related ones.
Some users have reverted to downgrading to Mavericks.
Are you at least sure your OS and Photoshop are fully updated?