Since the image appears in Orthodox icons earlier than Roman Catholica
painting, I emailed the Orthodox Church in America, which has an
excellent web site and welcomes questions. Today I received a very
thorough reply, the gist of which is that most "action" in icons happens
left to right, and that, in the two icon writing handbooks he consulted,
there is no other symbolism involved. He continued to tell me that often
symbolism is attached to items in icons when there really is not any
intended.
I really appreciated the thorough and thoughtful response, and recommend
the site if you have any icon-related questions.