There are three additional classes, S11, S12 and S13, for visually impaired swimmers. The lower number indicates a greater degree of impairment: class S11 swimmers are blind or nearly blind, and compete in blacked-out goggles. They each have a "tapper" who uses a pole or "bonker" to warn the swimmer that they are approaching the end of the pool. The visual classifications are based on medical classification, and not on functional mobility. One more class, S14, is for intellectually disabled swimmers. This class was not contested at the 2004 and the 2008 Summer Paralympics after the International Paralympic Committee (IPC) dropped all intellectual disability events following the basketball ID controversy at the 2000 Summer Paralympics, but was restored for the 2012 Summer Paralympics.