How Visual Illusions Make Your Brain Flip  It's a big skull. No,
wait, it's two people under an arch. Hold on, it's a skull
again. Two very different images can be perceived in this trick
picture and now we are one step closer to working out how the
brain spontaneously flips between such views, with the discovery
of what may be the relevant brain region.  The precise neural
mechanism that provokes the brain to switch its view of a scene
is unknown, but it is thought to play a major role in perception
by acting as a sort of reality check, says Ryota Kanai of
University College London. "We need a trigger to prompt possible
different interpretations so that we don't get stuck with a
potentially incorrect interpretation of the world."  Click to
view  To find out which part of the brain might be involved,
Kanai and colleagues asked 52 volunteers to watch a video of a
revolving sphere and press a button when the rotation of the
sphere appeared to change direction. Crucially, the sphere was
not changing direction; i