The Introverted Sensation type is the one that I had the most trouble comprehending when I read through that paper, largely because Jung did not describe it with any great clarity. Almost everything he says about the type is a description of how it devalues external objects, which is only one half of the picture, or of superficial behaviors associated with the type. He doesn't really get into the deeper mentality of the Introverted Sensation type or explain what, precisely, introverted sensation considered by itself actually is.

I don't have a clear type in Socionics, but between Ignoring and PoLR, Si is far more likely to be my PoLR.