 One reason why perceptual learning is a good instrument for explaining away putative cases of cognitive penetration is the following. In cases of perceptual learning, it is the external environment that drives the perceptual changes. As Raftopoulos puts it, “perceptual learning does not necessarily involve cognitive top-down penetrability but only data-driven processes” (2001: 493). For putative cases of cognitive penetration, the strategy for the perceptual learning theorist is to show how the perceptual changes involved may have been data-driven instead of top-down. Several philosophers have used this strategy at times, including Pylyshyn (1999: section 6.3), Brogaard and Gatzia (2015: 2), as well as Stokes (2015: 94), and Deroy (2013) might be interpreted in that way as well.