How "Human" are wraiths?

[Tinman]

I've been contemplating this for a while... exactly how much humanity remains to the ring wraiths? Are they completely mindless? being actively controlled by Sauron? Are they capable of independent thought? Or are they more like robots?

This varries greatly depending on the source. The animated film would have us believe they are like lurching zombies.... while the jackson film seems more like unyeilding ghost warriors.

The books view is what im most interested in though... Gloin/Gimli say that one of them came to eribor to negotiate for the dwarf rings... are they still capable of social interactions then? Or was it more like he showed up with a paper listing Saurons demands and just handed it off?

I know the witchking and gandalf exchange words, as well as the shield maden (can't spell eyowen, and am too lazy to look it up ), but the witchking seems to be slightly different from the 8...