Application Switcher slow draw/refresh
It turns out that, somehow, the graphics chip was no longer recognized by the OS when these problems started.  The flashing and flickering was apparently due to the slow processing of fade-in and fade-out animations when these animations were rendered by software instead of hardware.

I know this because I downloaded Maxon Cinebench and it told me my graphics card was "Apple Software Renderer."  When I rebooted the graphics card then showed as "NVIDIA GeForce 320M OpenGL Engine."

I don't know why the OS did not recognize the Nvidia graphics chip but I assume it will happen again which would give me a clue what caused it.