the center strip is probably connected to something, the sony psp uses one that looks like the same setup and it fits against the metal cage (or at-least in the 1000 models)
all else fails it's probably intended to be wired up like a rheostat
each pad is a "end" to a variable resistor (*2 for x and y)
that's a common joystick thing from the old days
apple //, c-64, and pc used that setup to change the clocks on 555 single shot timers, depending on how long the clock was high was representative of position