Some of the constraints on how fast we can task-switch or observe simultaneously aren't fixed. They can be trained by playing first-person-shooter video games.
Concrete ideas to modify and expand this hack go here.
Freeform discussion of this hack goes here.
Errata go here.
This hack is excerpted from Mind Hacks, by Tom Stafford and Matt Webb, in which it appears as Hack #43.
This is a page for a hack from the book MindPerformanceHacks by Ron Hale-Evans.