Who pays the bill?

"11.4% of authors from the peripheral countries are ready to treat their own money as a resource that may cover Article Processing Charges, which is true for only 6.1% of those based in the core countries. In the global periphery, academic authors have less access to grant funding that would cover publication fees. However, due to the substitution of their own money, authors from less wealthy countries are able to pay APCs as often as their richer colleagues."