Suzanne, your comment about the buzzing of cicadas is brilliant! I've often wondered what he was driving at with these pictures. My initial reaction was that he was using the pictures to show an abstract depiction of what sound might look like if given visual form, but I wonder if I only thought that because of the visual representations of sound I got as a child from Fantasia or from later exposure to oscilliscopes. The idea that the picture can show not only a visual record of the scene but also the sound of the scene through visual manipulation is really interesting.
I don't recall reading anything where he talks about these photos. Does anyone know of a source?