 The psychology literature provides ample evidence of perceptual learning. Goldstone (1998) helpfully distinguishes between four different types of perceptual learning in the literature: differentiation, unitization, attentional weighting, and stimulus imprinting. This section surveys these four types of perceptual learning (for further review, see Goldstone 2003; Goldstone, Braithwaite, &amp; Byrge 2012; and Goldstone &amp; Byrge 2015).