Sorry Pale, but the PA-50 does not sport the aftertouch function. In fact the biggest difference with the (much more expensive PA-80 model). Style-wise these two arranger boardd are 100% identical !!!
Of course you can always use the joystick to bend notes and ,in a limited way , I suppose you can also assign pitchbend to the third slider which is assignable.
(the other two sliders are for overall volume and for volume main/accom.