Stumbled upon this in a paper i’m reading and nearly wet myself (Cecil has a column on one-handed clapping, of course). Anosognosia is a condition where a patient is genuinely overtly unaware of their injuries. In the case of Mrs. D, she has a paralyzed left hand and vehemently denies it.
…Yet she was densely anosognosic, denying that her left hand was paralyzed. When I grabbed it, raised it toward her nose, and asked whose hand it was she said “It is your hand, doctor”. (This cannot be ascribed to confusion; when I gripped my student’s hand and held it under her nose she said “that is her hand” pointing to my student).
When asked whether she could point to my nose with her left hand she said she could. I then actually asked her to point and asked “Mrs. D, are you now pointing to my nose?” She said, “Yes I am.” “Can you clearly see it pointing?” I asked. “Yes I can, it is about 2 inches from your nose,” she replied.
Last I asked Mrs. D to clap her hands and she proceeded to do so with gusto, making clapping movements with her right hand alone, as though “clapping” an imaginary left hand! When asked whether she was clapping successfully she said “yes,” without hesitation. (Thus, we may, at last, have an answer to the Zen Master’s riddle “What is the sound of one hand clapping?” Mrs. D. obviously knew the answer! (Anosognosia in parietal Lobe Syndrome , Ramachandran, 2005)