Dynamic single target on E-5
Hit and hold AF target direct button (one to the right of Fn, marked [- - -] ). While you are holding it, three marks at the bottom light in yellow (All, Single target, Dynamic Single target), and you can move between them with rear dial
That was confusing me, too. Didn't think to hold it down. Bit of a nuisance going off into the menu each time to reactivate dynamic target mode.
(I am reading the manual. Just not comprehending it fully, I guess.)