Quick note on the Ponzo illusion: In my view, seeing the top bar as longer is actually a more primitive, fundamental observation. The idea that the bars ought to appear as the same length is an additional interpretative layer thrown on top of this, justified by geometric principles and theories about human visual perception. The direct (or “raw”) observation, however, is that the top bar appears longer.
Quick note on the Ponzo illusion: In my view, seeing the top bar as longer is actually a more primitive, fundamental observation. The idea that the bars ought to appear as the same length is an additional interpretative layer thrown on top of this, justified by geometric principles and theories about human visual perception. The direct (or “raw”) observation, however, is that the top bar appears longer.