"Used for an octave harmony effect on Where I End And You Begin. Some claim that it was a Boss PS3, but since the few blurry screencaps seem to include the white tipped knobs of the PS2,and since Radiohead sold a “ps2” on ebay, it is far more likely a PS2."
The XTDP website features [a brief interview/quote from Julian](http://extendplay.blogspot.com/2013/04/kitchens-of-distinction.html) wherein he reveals some of the gear used during KoD's heyday. Among his pedals, he lists a PS-2.
I got the Boss PS-2 from my friend that has his uncle gave it to him. One thing is interesting for sure that it has a some kind of octaver that can be used for some shimmer type sounds with use of other pedals.