Lost edges

In our fourth class, Dick pointed out "lost edges", where the artist invites the viewer to participate by filling in missing information, such as the Mona Lisa's hairline on the right side of the painting, where the area is shadowed, leaving the dividing line indistinct. Coincidentally, he got one of his "Twice-weekly letters" from Robert Genn the same day, making the same point (though using the terms "selective focus", "hard edges", and "soft edges") with work by a contemporary artist and by Titian, who we'd also discussed that day. See Robert Genn's commentary, and the works he refers to. Dick's comment, when he forwarded Genn's letter, was

To all who paid attention in class today, you may find this quite a coincidence.

The slides illustrating Dick's lecture are here, and the day's quiz is here.