Full Idea
Most feelings are experienced as pleasant or painful, but it is not evident that they all are; curiosity may be one that is not. [note: 'curiosity' may not be the name of a feeling, but a feeling typically accompanies it]
Gist of Idea
The feeling accompanying curiosity is neither pleasant nor painful
Source
Linda Trinkaus Zagzebski (Virtues of the Mind [1996], II 3.1)
Book Reference
Zagzebski,Linda: 'Virtues of the Mind' [CUP 1996], p.144
A Reaction
If a machine generates a sliding scale from pain to pleasure, is there a neutral feeling at the midpoint, or does all feeling briefly vanish there? Not sure.