Really stark results in that paper! I definitely encourage folks to check out the preprint so you can see the illusions for yourselves. While I fell strongly for all the illusions with large differences between urban and rural participants, I was totally flummoxed by the contrast illusion which was used to demonstrate that there are certain illusions which are strongly experienced cross-culturally (the image they used is in the appendices of the paper). I actually thought there might be something wrong with the image or my display, so I went on the illusion's Wikipedia page and was still not remotely fooled by any of the examples. According to that same Wikipedia page, there's a strong correlation between schizophrenia and not being affected by this illusion. I'm not schizophrenic (and it's worth noting that 19% of the UK/US participants in this post's study also didn't fall for it, presumably not all schizophrenic), but it was still an interesting tidbit.