 Recall that cases of cognitive penetration are cases where one’s beliefs, thoughts, or desires influence one’s perception (see Macpherson 2012: 24). One role of perceptual learning in the philosophical literature has been to explain away putative cases of cognitive penetration. For instance, it might seem at first glance that Siegel’s pine tree case is a case of cognitive penetration, a case where one’s newly acquired concept of a pine tree influences one’s perception. Connolly (2014b) and Arstila (2016), however, have both argued that the best way to understand Siegel’s pine tree case is not as a case of cognitive penetration, but rather through the particular mechanisms of perceptual learning. Connolly counts it as a case of attentional weighting, while Arstila understands it as involving both unitization and differentiation. 