Andrew Howley reports on a new paper that argues you can find in cave drawings and a carving of a bison/mammoth that not only do "the animals share a contour or a few lines, but that just two small details allow the entire image to be read as either of the two species, and seeing one causes the other to 'disappear.'":
The details in question are the eyes. [Duncan] Caldwell describes how there is "both an upper eye, which turns the crescent beneath it into a tusk, and lower eye, beside the front leg, that transforms the same crescent which we just interpreted as a "tusk", into a bison's overhead horn." Looking back and forth between the eyes then, we are able to see the entire shape transform from one animal to the other, an effect much more like the classic Gestalt shift of the duck-rabbit....
If Caldwell's analysis of the mammoth-bison phenomenon is correct, we begin to get a view not only of what prehistoric people saw, but also how they thought, and that has the potential to change our perspective and how we see other artifacts as well.
That perspective shift is also what makes these ambiguity illusions so appealing in the first place. Nigel Warburton said he chose the duck-rabbit as the logo for "Philosophy Bites" because it's also what he likes about philosophy itself. "Part of what philosophy does," he said "is, sometimes, make you see what you already knew in a completely different light." Perhaps someone enjoyed the same thought sitting in a cave, some 15,000 years ago.