When we were discussing vision and talking about optical illusions, I looked up some more and became obsessed with this optical illusion of a spinning dancer. When it was first shown to me, I felt l it took forever for me to see the girl rotating in the opposite direction. I saw her spinning counter-clockwise first and could not perceive her spinning clockwise no matter how long I stared at her or however many seconds I looked away. The second time I saw the video with a fresh pair of eyes, I perceived her spinning clockwise and could not see her spinning in the opposite way. Even after I saw the second video with the outline, I continue to have a hard time seeing the girl spinning in both ways if I perceive her spinning in one direction (even if I look away for a moment and return to focusing on the image).
The spinning dancer
The solution to the spinning dancer: