Some examples are:
- Vertical screen "tearing" during window transitions or window dragging.
- Sections of the screen that flash or appear to flicker, such as scroll bars or the Safari progress bar.
- Overall slower video performance.
- General graphics distortion or video anomalies.
Exit OS X recovery mode or safe mode and start OS X fully.
If you continue to have graphics issues, be sure you have the right OS X version (build) for your computer.