Full Idea
An ornithological Mary might know everything theoretical about kestrels, but be blind from birth, then have her sight restored. She now knows "That bird eats mice", so visual kestrels must be ontologically distinct from theoretical ones.
Gist of Idea
If a blind persons suddenly sees a kestrel, that doesn't make visual and theoretical kestrels different
Source
comment on Frank Jackson (Epiphenomenal Qualia [1982]) by David Papineau - Thinking about Consciousness 6.3
Book Reference
Papineau,David: 'Thinking about Consciousness' [OUP 2004], p.166
A Reaction
A nice reductio, and I think this pinpoints best what is wrong with the knowledge argument. Knowledge, and the means of acquiring it, are two distinct things. When I see x, I don't acquire knowledge of x, AND knowledge of my seeing x.